Stage #1 of core breakup: move everything under lib

19 files changed, 3462 insertions, 0 deletions

diff --git a/src/core/lib/channel/channel_args.c b/src/core/lib/channel/channel_args.c
new file mode 100644
index 0000000000..e0382fa0d9
--- /dev/null
+++ b/src/core/lib/channel/channel_args.c
@@ -0,0 +1,271 @@
+/*
+ *
+ * Copyright 2015-2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/channel/channel_args.h"
+#include <grpc/grpc.h>
+#include "src/core/support/string.h"
+
+#include <grpc/census.h>
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+#include <grpc/support/string_util.h>
+#include <grpc/support/useful.h>
+
+#include <string.h>
+
+static grpc_arg copy_arg(const grpc_arg *src) {
+  grpc_arg dst;
+  dst.type = src->type;
+  dst.key = gpr_strdup(src->key);
+  switch (dst.type) {
+    case GRPC_ARG_STRING:
+      dst.value.string = gpr_strdup(src->value.string);
+      break;
+    case GRPC_ARG_INTEGER:
+      dst.value.integer = src->value.integer;
+      break;
+    case GRPC_ARG_POINTER:
+      dst.value.pointer = src->value.pointer;
+      dst.value.pointer.p =
+          src->value.pointer.vtable->copy(src->value.pointer.p);
+      break;
+  }
+  return dst;
+}
+
+grpc_channel_args *grpc_channel_args_copy_and_add(const grpc_channel_args *src,
+                                                  const grpc_arg *to_add,
+                                                  size_t num_to_add) {
+  grpc_channel_args *dst = gpr_malloc(sizeof(grpc_channel_args));
+  size_t i;
+  size_t src_num_args = (src == NULL) ? 0 : src->num_args;
+  if (!src && !to_add) {
+    dst->num_args = 0;
+    dst->args = NULL;
+    return dst;
+  }
+  dst->num_args = src_num_args + num_to_add;
+  dst->args = gpr_malloc(sizeof(grpc_arg) * dst->num_args);
+  for (i = 0; i < src_num_args; i++) {
+    dst->args[i] = copy_arg(&src->args[i]);
+  }
+  for (i = 0; i < num_to_add; i++) {
+    dst->args[i + src_num_args] = copy_arg(&to_add[i]);
+  }
+  return dst;
+}
+
+grpc_channel_args *grpc_channel_args_copy(const grpc_channel_args *src) {
+  return grpc_channel_args_copy_and_add(src, NULL, 0);
+}
+
+grpc_channel_args *grpc_channel_args_merge(const grpc_channel_args *a,
+                                           const grpc_channel_args *b) {
+  return grpc_channel_args_copy_and_add(a, b->args, b->num_args);
+}
+
+static int cmp_arg(const grpc_arg *a, const grpc_arg *b) {
+  int c = GPR_ICMP(a->type, b->type);
+  if (c != 0) return c;
+  c = strcmp(a->key, b->key);
+  if (c != 0) return c;
+  switch (a->type) {
+    case GRPC_ARG_STRING:
+      return strcmp(a->value.string, b->value.string);
+    case GRPC_ARG_INTEGER:
+      return GPR_ICMP(a->value.integer, b->value.integer);
+    case GRPC_ARG_POINTER:
+      c = GPR_ICMP(a->value.pointer.p, b->value.pointer.p);
+      if (c != 0) {
+        c = GPR_ICMP(a->value.pointer.vtable, b->value.pointer.vtable);
+        if (c == 0) {
+          c = a->value.pointer.vtable->cmp(a->value.pointer.p,
+                                           b->value.pointer.p);
+        }
+      }
+      return c;
+  }
+  GPR_UNREACHABLE_CODE(return 0);
+}
+
+/* stabilizing comparison function: since channel_args ordering matters for
+ * keys with the same name, we need to preserve that ordering */
+static int cmp_key_stable(const void *ap, const void *bp) {
+  const grpc_arg *const *a = ap;
+  const grpc_arg *const *b = bp;
+  int c = strcmp((*a)->key, (*b)->key);
+  if (c == 0) c = GPR_ICMP(*a, *b);
+  return c;
+}
+
+grpc_channel_args *grpc_channel_args_normalize(const grpc_channel_args *a) {
+  grpc_arg **args = gpr_malloc(sizeof(grpc_arg *) * a->num_args);
+  for (size_t i = 0; i < a->num_args; i++) {
+    args[i] = &a->args[i];
+  }
+  qsort(args, a->num_args, sizeof(grpc_arg *), cmp_key_stable);
+
+  grpc_channel_args *b = gpr_malloc(sizeof(grpc_channel_args));
+  b->num_args = a->num_args;
+  b->args = gpr_malloc(sizeof(grpc_arg) * b->num_args);
+  for (size_t i = 0; i < a->num_args; i++) {
+    b->args[i] = copy_arg(args[i]);
+  }
+
+  gpr_free(args);
+  return b;
+}
+
+void grpc_channel_args_destroy(grpc_channel_args *a) {
+  size_t i;
+  for (i = 0; i < a->num_args; i++) {
+    switch (a->args[i].type) {
+      case GRPC_ARG_STRING:
+        gpr_free(a->args[i].value.string);
+        break;
+      case GRPC_ARG_INTEGER:
+        break;
+      case GRPC_ARG_POINTER:
+        a->args[i].value.pointer.vtable->destroy(a->args[i].value.pointer.p);
+        break;
+    }
+    gpr_free(a->args[i].key);
+  }
+  gpr_free(a->args);
+  gpr_free(a);
+}
+
+int grpc_channel_args_is_census_enabled(const grpc_channel_args *a) {
+  size_t i;
+  if (a == NULL) return 0;
+  for (i = 0; i < a->num_args; i++) {
+    if (0 == strcmp(a->args[i].key, GRPC_ARG_ENABLE_CENSUS)) {
+      return a->args[i].value.integer != 0 && census_enabled();
+    }
+  }
+  return census_enabled();
+}
+
+grpc_compression_algorithm grpc_channel_args_get_compression_algorithm(
+    const grpc_channel_args *a) {
+  size_t i;
+  if (a == NULL) return 0;
+  for (i = 0; i < a->num_args; ++i) {
+    if (a->args[i].type == GRPC_ARG_INTEGER &&
+        !strcmp(GRPC_COMPRESSION_ALGORITHM_ARG, a->args[i].key)) {
+      return (grpc_compression_algorithm)a->args[i].value.integer;
+      break;
+    }
+  }
+  return GRPC_COMPRESS_NONE;
+}
+
+grpc_channel_args *grpc_channel_args_set_compression_algorithm(
+    grpc_channel_args *a, grpc_compression_algorithm algorithm) {
+  grpc_arg tmp;
+  tmp.type = GRPC_ARG_INTEGER;
+  tmp.key = GRPC_COMPRESSION_ALGORITHM_ARG;
+  tmp.value.integer = algorithm;
+  return grpc_channel_args_copy_and_add(a, &tmp, 1);
+}
+
+/** Returns 1 if the argument for compression algorithm's enabled states bitset
+ * was found in \a a, returning the arg's value in \a states. Otherwise, returns
+ * 0. */
+static int find_compression_algorithm_states_bitset(const grpc_channel_args *a,
+                                                    int **states_arg) {
+  if (a != NULL) {
+    size_t i;
+    for (i = 0; i < a->num_args; ++i) {
+      if (a->args[i].type == GRPC_ARG_INTEGER &&
+          !strcmp(GRPC_COMPRESSION_ALGORITHM_STATE_ARG, a->args[i].key)) {
+        *states_arg = &a->args[i].value.integer;
+        return 1; /* GPR_TRUE */
+      }
+    }
+  }
+  return 0; /* GPR_FALSE */
+}
+
+grpc_channel_args *grpc_channel_args_compression_algorithm_set_state(
+    grpc_channel_args **a, grpc_compression_algorithm algorithm, int state) {
+  int *states_arg;
+  grpc_channel_args *result = *a;
+  const int states_arg_found =
+      find_compression_algorithm_states_bitset(*a, &states_arg);
+
+  if (states_arg_found) {
+    if (state != 0) {
+      GPR_BITSET((unsigned *)states_arg, algorithm);
+    } else {
+      GPR_BITCLEAR((unsigned *)states_arg, algorithm);
+    }
+  } else {
+    /* create a new arg */
+    grpc_arg tmp;
+    tmp.type = GRPC_ARG_INTEGER;
+    tmp.key = GRPC_COMPRESSION_ALGORITHM_STATE_ARG;
+    /* all enabled by default */
+    tmp.value.integer = (1u << GRPC_COMPRESS_ALGORITHMS_COUNT) - 1;
+    if (state != 0) {
+      GPR_BITSET((unsigned *)&tmp.value.integer, algorithm);
+    } else {
+      GPR_BITCLEAR((unsigned *)&tmp.value.integer, algorithm);
+    }
+    result = grpc_channel_args_copy_and_add(*a, &tmp, 1);
+    grpc_channel_args_destroy(*a);
+    *a = result;
+  }
+  return result;
+}
+
+int grpc_channel_args_compression_algorithm_get_states(
+    const grpc_channel_args *a) {
+  int *states_arg;
+  if (find_compression_algorithm_states_bitset(a, &states_arg)) {
+    return *states_arg;
+  } else {
+    return (1u << GRPC_COMPRESS_ALGORITHMS_COUNT) - 1; /* All algs. enabled */
+  }
+}
+
+int grpc_channel_args_compare(const grpc_channel_args *a,
+                              const grpc_channel_args *b) {
+  int c = GPR_ICMP(a->num_args, b->num_args);
+  if (c != 0) return c;
+  for (size_t i = 0; i < a->num_args; i++) {
+    c = cmp_arg(&a->args[i], &b->args[i]);
+    if (c != 0) return c;
+  }
+  return 0;
+}
diff --git a/src/core/lib/channel/channel_args.h b/src/core/lib/channel/channel_args.h
new file mode 100644
index 0000000000..e19440f76f
--- /dev/null
+++ b/src/core/lib/channel/channel_args.h
@@ -0,0 +1,94 @@
+/*
+ *
+ * Copyright 2015-2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_CHANNEL_CHANNEL_ARGS_H
+#define GRPC_CORE_CHANNEL_CHANNEL_ARGS_H
+
+#include <grpc/compression.h>
+#include <grpc/grpc.h>
+
+/* Copy some arguments */
+grpc_channel_args *grpc_channel_args_copy(const grpc_channel_args *src);
+
+/* Copy some arguments, stably sorting keys */
+grpc_channel_args *grpc_channel_args_normalize(const grpc_channel_args *a);
+
+/** Copy some arguments and add the to_add parameter in the end.
+   If to_add is NULL, it is equivalent to call grpc_channel_args_copy. */
+grpc_channel_args *grpc_channel_args_copy_and_add(const grpc_channel_args *src,
+                                                  const grpc_arg *to_add,
+                                                  size_t num_to_add);
+
+/** Copy args from a then args from b into a new channel args */
+grpc_channel_args *grpc_channel_args_merge(const grpc_channel_args *a,
+                                           const grpc_channel_args *b);
+
+/** Destroy arguments created by grpc_channel_args_copy */
+void grpc_channel_args_destroy(grpc_channel_args *a);
+
+/** Reads census_enabled settings from channel args. Returns 1 if census_enabled
+ * is specified in channel args, otherwise returns 0. */
+int grpc_channel_args_is_census_enabled(const grpc_channel_args *a);
+
+/** Returns the compression algorithm set in \a a. */
+grpc_compression_algorithm grpc_channel_args_get_compression_algorithm(
+    const grpc_channel_args *a);
+
+/** Returns a channel arg instance with compression enabled. If \a a is
+ * non-NULL, its args are copied. N.B. GRPC_COMPRESS_NONE disables compression
+ * for the channel. */
+grpc_channel_args *grpc_channel_args_set_compression_algorithm(
+    grpc_channel_args *a, grpc_compression_algorithm algorithm);
+
+/** Sets the support for the given compression algorithm. By default, all
+ * compression algorithms are enabled. It's an error to disable an algorithm set
+ * by grpc_channel_args_set_compression_algorithm.
+ *
+ * Returns an instance with the updated algorithm states. The \a a pointer is
+ * modified to point to the returned instance (which may be different from the
+ * input value of \a a). */
+grpc_channel_args *grpc_channel_args_compression_algorithm_set_state(
+    grpc_channel_args **a, grpc_compression_algorithm algorithm, int enabled);
+
+/** Returns the bitset representing the support state (true for enabled, false
+ * for disabled) for compression algorithms.
+ *
+ * The i-th bit of the returned bitset corresponds to the i-th entry in the
+ * grpc_compression_algorithm enum. */
+int grpc_channel_args_compression_algorithm_get_states(
+    const grpc_channel_args *a);
+
+int grpc_channel_args_compare(const grpc_channel_args *a,
+                              const grpc_channel_args *b);
+
+#endif /* GRPC_CORE_CHANNEL_CHANNEL_ARGS_H */
diff --git a/src/core/lib/channel/channel_stack.c b/src/core/lib/channel/channel_stack.c
new file mode 100644
index 0000000000..3e61688364
--- /dev/null
+++ b/src/core/lib/channel/channel_stack.c
@@ -0,0 +1,262 @@
+/*
+ *
+ * Copyright 2015, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/channel/channel_stack.h"
+#include <grpc/support/log.h>
+
+#include <stdlib.h>
+#include <string.h>
+
+int grpc_trace_channel = 0;
+
+/* Memory layouts.
+
+   Channel stack is laid out as: {
+     grpc_channel_stack stk;
+     padding to GPR_MAX_ALIGNMENT
+     grpc_channel_element[stk.count];
+     per-filter memory, aligned to GPR_MAX_ALIGNMENT
+   }
+
+   Call stack is laid out as: {
+     grpc_call_stack stk;
+     padding to GPR_MAX_ALIGNMENT
+     grpc_call_element[stk.count];
+     per-filter memory, aligned to GPR_MAX_ALIGNMENT
+   } */
+
+/* Given a size, round up to the next multiple of sizeof(void*) */
+#define ROUND_UP_TO_ALIGNMENT_SIZE(x) \
+  (((x) + GPR_MAX_ALIGNMENT - 1u) & ~(GPR_MAX_ALIGNMENT - 1u))
+
+size_t grpc_channel_stack_size(const grpc_channel_filter **filters,
+                               size_t filter_count) {
+  /* always need the header, and size for the channel elements */
+  size_t size =
+      ROUND_UP_TO_ALIGNMENT_SIZE(sizeof(grpc_channel_stack)) +
+      ROUND_UP_TO_ALIGNMENT_SIZE(filter_count * sizeof(grpc_channel_element));
+  size_t i;
+
+  GPR_ASSERT((GPR_MAX_ALIGNMENT & (GPR_MAX_ALIGNMENT - 1)) == 0 &&
+             "GPR_MAX_ALIGNMENT must be a power of two");
+
+  /* add the size for each filter */
+  for (i = 0; i < filter_count; i++) {
+    size += ROUND_UP_TO_ALIGNMENT_SIZE(filters[i]->sizeof_channel_data);
+  }
+
+  return size;
+}
+
+#define CHANNEL_ELEMS_FROM_STACK(stk)                                   \
+  ((grpc_channel_element *)((char *)(stk) + ROUND_UP_TO_ALIGNMENT_SIZE( \
+                                                sizeof(grpc_channel_stack))))
+
+#define CALL_ELEMS_FROM_STACK(stk)       \
+  ((grpc_call_element *)((char *)(stk) + \
+                         ROUND_UP_TO_ALIGNMENT_SIZE(sizeof(grpc_call_stack))))
+
+grpc_channel_element *grpc_channel_stack_element(
+    grpc_channel_stack *channel_stack, size_t index) {
+  return CHANNEL_ELEMS_FROM_STACK(channel_stack) + index;
+}
+
+grpc_channel_element *grpc_channel_stack_last_element(
+    grpc_channel_stack *channel_stack) {
+  return grpc_channel_stack_element(channel_stack, channel_stack->count - 1);
+}
+
+grpc_call_element *grpc_call_stack_element(grpc_call_stack *call_stack,
+                                           size_t index) {
+  return CALL_ELEMS_FROM_STACK(call_stack) + index;
+}
+
+void grpc_channel_stack_init(grpc_exec_ctx *exec_ctx, int initial_refs,
+                             grpc_iomgr_cb_func destroy, void *destroy_arg,
+                             const grpc_channel_filter **filters,
+                             size_t filter_count,
+                             const grpc_channel_args *channel_args,
+                             const char *name, grpc_channel_stack *stack) {
+  size_t call_size =
+      ROUND_UP_TO_ALIGNMENT_SIZE(sizeof(grpc_call_stack)) +
+      ROUND_UP_TO_ALIGNMENT_SIZE(filter_count * sizeof(grpc_call_element));
+  grpc_channel_element *elems;
+  grpc_channel_element_args args;
+  char *user_data;
+  size_t i;
+
+  stack->count = filter_count;
+  GRPC_STREAM_REF_INIT(&stack->refcount, initial_refs, destroy, destroy_arg,
+                       name);
+  elems = CHANNEL_ELEMS_FROM_STACK(stack);
+  user_data =
+      ((char *)elems) +
+      ROUND_UP_TO_ALIGNMENT_SIZE(filter_count * sizeof(grpc_channel_element));
+
+  /* init per-filter data */
+  for (i = 0; i < filter_count; i++) {
+    args.channel_stack = stack;
+    args.channel_args = channel_args;
+    args.is_first = i == 0;
+    args.is_last = i == (filter_count - 1);
+    elems[i].filter = filters[i];
+    elems[i].channel_data = user_data;
+    elems[i].filter->init_channel_elem(exec_ctx, &elems[i], &args);
+    user_data += ROUND_UP_TO_ALIGNMENT_SIZE(filters[i]->sizeof_channel_data);
+    call_size += ROUND_UP_TO_ALIGNMENT_SIZE(filters[i]->sizeof_call_data);
+  }
+
+  GPR_ASSERT(user_data > (char *)stack);
+  GPR_ASSERT((uintptr_t)(user_data - (char *)stack) ==
+             grpc_channel_stack_size(filters, filter_count));
+
+  stack->call_stack_size = call_size;
+}
+
+void grpc_channel_stack_destroy(grpc_exec_ctx *exec_ctx,
+                                grpc_channel_stack *stack) {
+  grpc_channel_element *channel_elems = CHANNEL_ELEMS_FROM_STACK(stack);
+  size_t count = stack->count;
+  size_t i;
+
+  /* destroy per-filter data */
+  for (i = 0; i < count; i++) {
+    channel_elems[i].filter->destroy_channel_elem(exec_ctx, &channel_elems[i]);
+  }
+}
+
+void grpc_call_stack_init(grpc_exec_ctx *exec_ctx,
+                          grpc_channel_stack *channel_stack, int initial_refs,
+                          grpc_iomgr_cb_func destroy, void *destroy_arg,
+                          grpc_call_context_element *context,
+                          const void *transport_server_data,
+                          grpc_call_stack *call_stack) {
+  grpc_channel_element *channel_elems = CHANNEL_ELEMS_FROM_STACK(channel_stack);
+  grpc_call_element_args args;
+  size_t count = channel_stack->count;
+  grpc_call_element *call_elems;
+  char *user_data;
+  size_t i;
+
+  call_stack->count = count;
+  GRPC_STREAM_REF_INIT(&call_stack->refcount, initial_refs, destroy,
+                       destroy_arg, "CALL_STACK");
+  call_elems = CALL_ELEMS_FROM_STACK(call_stack);
+  user_data = ((char *)call_elems) +
+              ROUND_UP_TO_ALIGNMENT_SIZE(count * sizeof(grpc_call_element));
+
+  /* init per-filter data */
+  for (i = 0; i < count; i++) {
+    args.call_stack = call_stack;
+    args.server_transport_data = transport_server_data;
+    args.context = context;
+    call_elems[i].filter = channel_elems[i].filter;
+    call_elems[i].channel_data = channel_elems[i].channel_data;
+    call_elems[i].call_data = user_data;
+    call_elems[i].filter->init_call_elem(exec_ctx, &call_elems[i], &args);
+    user_data +=
+        ROUND_UP_TO_ALIGNMENT_SIZE(call_elems[i].filter->sizeof_call_data);
+  }
+}
+
+void grpc_call_stack_set_pollset(grpc_exec_ctx *exec_ctx,
+                                 grpc_call_stack *call_stack,
+                                 grpc_pollset *pollset) {
+  size_t count = call_stack->count;
+  grpc_call_element *call_elems;
+  char *user_data;
+  size_t i;
+
+  call_elems = CALL_ELEMS_FROM_STACK(call_stack);
+  user_data = ((char *)call_elems) +
+              ROUND_UP_TO_ALIGNMENT_SIZE(count * sizeof(grpc_call_element));
+
+  /* init per-filter data */
+  for (i = 0; i < count; i++) {
+    call_elems[i].filter->set_pollset(exec_ctx, &call_elems[i], pollset);
+    user_data +=
+        ROUND_UP_TO_ALIGNMENT_SIZE(call_elems[i].filter->sizeof_call_data);
+  }
+}
+
+void grpc_call_stack_ignore_set_pollset(grpc_exec_ctx *exec_ctx,
+                                        grpc_call_element *elem,
+                                        grpc_pollset *pollset) {}
+
+void grpc_call_stack_destroy(grpc_exec_ctx *exec_ctx, grpc_call_stack *stack) {
+  grpc_call_element *elems = CALL_ELEMS_FROM_STACK(stack);
+  size_t count = stack->count;
+  size_t i;
+
+  /* destroy per-filter data */
+  for (i = 0; i < count; i++) {
+    elems[i].filter->destroy_call_elem(exec_ctx, &elems[i]);
+  }
+}
+
+void grpc_call_next_op(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
+                       grpc_transport_stream_op *op) {
+  grpc_call_element *next_elem = elem + 1;
+  next_elem->filter->start_transport_stream_op(exec_ctx, next_elem, op);
+}
+
+char *grpc_call_next_get_peer(grpc_exec_ctx *exec_ctx,
+                              grpc_call_element *elem) {
+  grpc_call_element *next_elem = elem + 1;
+  return next_elem->filter->get_peer(exec_ctx, next_elem);
+}
+
+void grpc_channel_next_op(grpc_exec_ctx *exec_ctx, grpc_channel_element *elem,
+                          grpc_transport_op *op) {
+  grpc_channel_element *next_elem = elem + 1;
+  next_elem->filter->start_transport_op(exec_ctx, next_elem, op);
+}
+
+grpc_channel_stack *grpc_channel_stack_from_top_element(
+    grpc_channel_element *elem) {
+  return (grpc_channel_stack *)((char *)(elem)-ROUND_UP_TO_ALIGNMENT_SIZE(
+      sizeof(grpc_channel_stack)));
+}
+
+grpc_call_stack *grpc_call_stack_from_top_element(grpc_call_element *elem) {
+  return (grpc_call_stack *)((char *)(elem)-ROUND_UP_TO_ALIGNMENT_SIZE(
+      sizeof(grpc_call_stack)));
+}
+
+void grpc_call_element_send_cancel(grpc_exec_ctx *exec_ctx,
+                                   grpc_call_element *cur_elem) {
+  grpc_transport_stream_op op;
+  memset(&op, 0, sizeof(op));
+  op.cancel_with_status = GRPC_STATUS_CANCELLED;
+  grpc_call_next_op(exec_ctx, cur_elem, &op);
+}
diff --git a/src/core/lib/channel/channel_stack.h b/src/core/lib/channel/channel_stack.h
new file mode 100644
index 0000000000..52362f0b20
--- /dev/null
+++ b/src/core/lib/channel/channel_stack.h
@@ -0,0 +1,260 @@
+/*
+ *
+ * Copyright 2015-2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_CHANNEL_CHANNEL_STACK_H
+#define GRPC_CORE_CHANNEL_CHANNEL_STACK_H
+
+/* A channel filter defines how operations on a channel are implemented.
+   Channel filters are chained together to create full channels, and if those
+   chains are linear, then channel stacks provide a mechanism to minimize
+   allocations for that chain.
+   Call stacks are created by channel stacks and represent the per-call data
+   for that stack. */
+
+#include <stddef.h>
+
+#include <grpc/grpc.h>
+#include <grpc/support/log.h>
+#include "src/core/debug/trace.h"
+#include "src/core/transport/transport.h"
+
+typedef struct grpc_channel_element grpc_channel_element;
+typedef struct grpc_call_element grpc_call_element;
+
+typedef struct grpc_channel_stack grpc_channel_stack;
+typedef struct grpc_call_stack grpc_call_stack;
+
+typedef struct {
+  grpc_channel_stack *channel_stack;
+  const grpc_channel_args *channel_args;
+  int is_first;
+  int is_last;
+} grpc_channel_element_args;
+
+typedef struct {
+  grpc_call_stack *call_stack;
+  const void *server_transport_data;
+  grpc_call_context_element *context;
+} grpc_call_element_args;
+
+/* Channel filters specify:
+   1. the amount of memory needed in the channel & call (via the sizeof_XXX
+      members)
+   2. functions to initialize and destroy channel & call data
+      (init_XXX, destroy_XXX)
+   3. functions to implement call operations and channel operations (call_op,
+      channel_op)
+   4. a name, which is useful when debugging
+
+   Members are laid out in approximate frequency of use order. */
+typedef struct {
+  /* Called to eg. send/receive data on a call.
+     See grpc_call_next_op on how to call the next element in the stack */
+  void (*start_transport_stream_op)(grpc_exec_ctx *exec_ctx,
+                                    grpc_call_element *elem,
+                                    grpc_transport_stream_op *op);
+  /* Called to handle channel level operations - e.g. new calls, or transport
+     closure.
+     See grpc_channel_next_op on how to call the next element in the stack */
+  void (*start_transport_op)(grpc_exec_ctx *exec_ctx,
+                             grpc_channel_element *elem, grpc_transport_op *op);
+
+  /* sizeof(per call data) */
+  size_t sizeof_call_data;
+  /* Initialize per call data.
+     elem is initialized at the start of the call, and elem->call_data is what
+     needs initializing.
+     The filter does not need to do any chaining.
+     server_transport_data is an opaque pointer. If it is NULL, this call is
+     on a client; if it is non-NULL, then it points to memory owned by the
+     transport and is on the server. Most filters want to ignore this
+     argument. */
+  void (*init_call_elem)(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
+                         grpc_call_element_args *args);
+  void (*set_pollset)(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
+                      grpc_pollset *pollset);
+  /* Destroy per call data.
+     The filter does not need to do any chaining */
+  void (*destroy_call_elem)(grpc_exec_ctx *exec_ctx, grpc_call_element *elem);
+
+  /* sizeof(per channel data) */
+  size_t sizeof_channel_data;
+  /* Initialize per-channel data.
+     elem is initialized at the start of the call, and elem->channel_data is
+     what needs initializing.
+     is_first, is_last designate this elements position in the stack, and are
+     useful for asserting correct configuration by upper layer code.
+     The filter does not need to do any chaining */
+  void (*init_channel_elem)(grpc_exec_ctx *exec_ctx, grpc_channel_element *elem,
+                            grpc_channel_element_args *args);
+  /* Destroy per channel data.
+     The filter does not need to do any chaining */
+  void (*destroy_channel_elem)(grpc_exec_ctx *exec_ctx,
+                               grpc_channel_element *elem);
+
+  /* Implement grpc_call_get_peer() */
+  char *(*get_peer)(grpc_exec_ctx *exec_ctx, grpc_call_element *elem);
+
+  /* The name of this filter */
+  const char *name;
+} grpc_channel_filter;
+
+/* A channel_element tracks its filter and the filter requested memory within
+   a channel allocation */
+struct grpc_channel_element {
+  const grpc_channel_filter *filter;
+  void *channel_data;
+};
+
+/* A call_element tracks its filter, the filter requested memory within
+   a channel allocation, and the filter requested memory within a call
+   allocation */
+struct grpc_call_element {
+  const grpc_channel_filter *filter;
+  void *channel_data;
+  void *call_data;
+};
+
+/* A channel stack tracks a set of related filters for one channel, and
+   guarantees they live within a single malloc() allocation */
+struct grpc_channel_stack {
+  grpc_stream_refcount refcount;
+  size_t count;
+  /* Memory required for a call stack (computed at channel stack
+     initialization) */
+  size_t call_stack_size;
+};
+
+/* A call stack tracks a set of related filters for one call, and guarantees
+   they live within a single malloc() allocation */
+struct grpc_call_stack {
+  /* shared refcount for this channel stack.
+     MUST be the first element: the underlying code calls destroy
+     with the address of the refcount, but higher layers prefer to think
+     about the address of the call stack itself. */
+  grpc_stream_refcount refcount;
+  size_t count;
+};
+
+/* Get a channel element given a channel stack and its index */
+grpc_channel_element *grpc_channel_stack_element(grpc_channel_stack *stack,
+                                                 size_t i);
+/* Get the last channel element in a channel stack */
+grpc_channel_element *grpc_channel_stack_last_element(
+    grpc_channel_stack *stack);
+/* Get a call stack element given a call stack and an index */
+grpc_call_element *grpc_call_stack_element(grpc_call_stack *stack, size_t i);
+
+/* Determine memory required for a channel stack containing a set of filters */
+size_t grpc_channel_stack_size(const grpc_channel_filter **filters,
+                               size_t filter_count);
+/* Initialize a channel stack given some filters */
+void grpc_channel_stack_init(grpc_exec_ctx *exec_ctx, int initial_refs,
+                             grpc_iomgr_cb_func destroy, void *destroy_arg,
+                             const grpc_channel_filter **filters,
+                             size_t filter_count, const grpc_channel_args *args,
+                             const char *name, grpc_channel_stack *stack);
+/* Destroy a channel stack */
+void grpc_channel_stack_destroy(grpc_exec_ctx *exec_ctx,
+                                grpc_channel_stack *stack);
+
+/* Initialize a call stack given a channel stack. transport_server_data is
+   expected to be NULL on a client, or an opaque transport owned pointer on the
+   server. */
+void grpc_call_stack_init(grpc_exec_ctx *exec_ctx,
+                          grpc_channel_stack *channel_stack, int initial_refs,
+                          grpc_iomgr_cb_func destroy, void *destroy_arg,
+                          grpc_call_context_element *context,
+                          const void *transport_server_data,
+                          grpc_call_stack *call_stack);
+/* Set a pollset for a call stack: must occur before the first op is started */
+void grpc_call_stack_set_pollset(grpc_exec_ctx *exec_ctx,
+                                 grpc_call_stack *call_stack,
+                                 grpc_pollset *pollset);
+
+#ifdef GRPC_STREAM_REFCOUNT_DEBUG
+#define GRPC_CALL_STACK_REF(call_stack, reason) \
+  grpc_stream_ref(&(call_stack)->refcount, reason)
+#define GRPC_CALL_STACK_UNREF(exec_ctx, call_stack, reason) \
+  grpc_stream_unref(exec_ctx, &(call_stack)->refcount, reason)
+#define GRPC_CHANNEL_STACK_REF(channel_stack, reason) \
+  grpc_stream_ref(&(channel_stack)->refcount, reason)
+#define GRPC_CHANNEL_STACK_UNREF(exec_ctx, channel_stack, reason) \
+  grpc_stream_unref(exec_ctx, &(channel_stack)->refcount, reason)
+#else
+#define GRPC_CALL_STACK_REF(call_stack, reason) \
+  grpc_stream_ref(&(call_stack)->refcount)
+#define GRPC_CALL_STACK_UNREF(exec_ctx, call_stack, reason) \
+  grpc_stream_unref(exec_ctx, &(call_stack)->refcount)
+#define GRPC_CHANNEL_STACK_REF(channel_stack, reason) \
+  grpc_stream_ref(&(channel_stack)->refcount)
+#define GRPC_CHANNEL_STACK_UNREF(exec_ctx, channel_stack, reason) \
+  grpc_stream_unref(exec_ctx, &(channel_stack)->refcount)
+#endif
+
+/* Destroy a call stack */
+void grpc_call_stack_destroy(grpc_exec_ctx *exec_ctx, grpc_call_stack *stack);
+
+/* Ignore set pollset - used by filters to implement the set_pollset method
+   if they don't care about pollsets at all. Does nothing. */
+void grpc_call_stack_ignore_set_pollset(grpc_exec_ctx *exec_ctx,
+                                        grpc_call_element *elem,
+                                        grpc_pollset *pollset);
+/* Call the next operation in a call stack */
+void grpc_call_next_op(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
+                       grpc_transport_stream_op *op);
+/* Call the next operation (depending on call directionality) in a channel
+   stack */
+void grpc_channel_next_op(grpc_exec_ctx *exec_ctx, grpc_channel_element *elem,
+                          grpc_transport_op *op);
+/* Pass through a request to get_peer to the next child element */
+char *grpc_call_next_get_peer(grpc_exec_ctx *exec_ctx, grpc_call_element *elem);
+
+/* Given the top element of a channel stack, get the channel stack itself */
+grpc_channel_stack *grpc_channel_stack_from_top_element(
+    grpc_channel_element *elem);
+/* Given the top element of a call stack, get the call stack itself */
+grpc_call_stack *grpc_call_stack_from_top_element(grpc_call_element *elem);
+
+void grpc_call_log_op(char *file, int line, gpr_log_severity severity,
+                      grpc_call_element *elem, grpc_transport_stream_op *op);
+
+void grpc_call_element_send_cancel(grpc_exec_ctx *exec_ctx,
+                                   grpc_call_element *cur_elem);
+
+extern int grpc_trace_channel;
+
+#define GRPC_CALL_LOG_OP(sev, elem, op) \
+  if (grpc_trace_channel) grpc_call_log_op(sev, elem, op)
+
+#endif /* GRPC_CORE_CHANNEL_CHANNEL_STACK_H */
diff --git a/src/core/lib/channel/channel_stack_builder.c b/src/core/lib/channel/channel_stack_builder.c
new file mode 100644
index 0000000000..1b1004e5f9
--- /dev/null
+++ b/src/core/lib/channel/channel_stack_builder.c
@@ -0,0 +1,258 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/channel/channel_stack_builder.h"
+
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+
+int grpc_trace_channel_stack_builder = 0;
+
+typedef struct filter_node {
+  struct filter_node *next;
+  struct filter_node *prev;
+  const grpc_channel_filter *filter;
+  grpc_post_filter_create_init_func init;
+  void *init_arg;
+} filter_node;
+
+struct grpc_channel_stack_builder {
+  // sentinel nodes for filters that have been added
+  filter_node begin;
+  filter_node end;
+  // various set/get-able parameters
+  const grpc_channel_args *args;
+  grpc_transport *transport;
+  const char *name;
+};
+
+struct grpc_channel_stack_builder_iterator {
+  grpc_channel_stack_builder *builder;
+  filter_node *node;
+};
+
+grpc_channel_stack_builder *grpc_channel_stack_builder_create(void) {
+  grpc_channel_stack_builder *b = gpr_malloc(sizeof(*b));
+  memset(b, 0, sizeof(*b));
+
+  b->begin.filter = NULL;
+  b->end.filter = NULL;
+  b->begin.next = &b->end;
+  b->begin.prev = &b->end;
+  b->end.next = &b->begin;
+  b->end.prev = &b->begin;
+
+  return b;
+}
+
+static grpc_channel_stack_builder_iterator *create_iterator_at_filter_node(
+    grpc_channel_stack_builder *builder, filter_node *node) {
+  grpc_channel_stack_builder_iterator *it = gpr_malloc(sizeof(*it));
+  it->builder = builder;
+  it->node = node;
+  return it;
+}
+
+void grpc_channel_stack_builder_iterator_destroy(
+    grpc_channel_stack_builder_iterator *it) {
+  gpr_free(it);
+}
+
+grpc_channel_stack_builder_iterator *
+grpc_channel_stack_builder_create_iterator_at_first(
+    grpc_channel_stack_builder *builder) {
+  return create_iterator_at_filter_node(builder, &builder->begin);
+}
+
+grpc_channel_stack_builder_iterator *
+grpc_channel_stack_builder_create_iterator_at_last(
+    grpc_channel_stack_builder *builder) {
+  return create_iterator_at_filter_node(builder, &builder->end);
+}
+
+bool grpc_channel_stack_builder_move_next(
+    grpc_channel_stack_builder_iterator *iterator) {
+  if (iterator->node == &iterator->builder->end) return false;
+  iterator->node = iterator->node->next;
+  return true;
+}
+
+bool grpc_channel_stack_builder_move_prev(
+    grpc_channel_stack_builder_iterator *iterator) {
+  if (iterator->node == &iterator->builder->begin) return false;
+  iterator->node = iterator->node->prev;
+  return true;
+}
+
+bool grpc_channel_stack_builder_move_prev(
+    grpc_channel_stack_builder_iterator *iterator);
+
+void grpc_channel_stack_builder_set_name(grpc_channel_stack_builder *builder,
+                                         const char *name) {
+  GPR_ASSERT(builder->name == NULL);
+  builder->name = name;
+}
+
+void grpc_channel_stack_builder_set_channel_arguments(
+    grpc_channel_stack_builder *builder, const grpc_channel_args *args) {
+  GPR_ASSERT(builder->args == NULL);
+  builder->args = args;
+}
+
+void grpc_channel_stack_builder_set_transport(
+    grpc_channel_stack_builder *builder, grpc_transport *transport) {
+  GPR_ASSERT(builder->transport == NULL);
+  builder->transport = transport;
+}
+
+grpc_transport *grpc_channel_stack_builder_get_transport(
+    grpc_channel_stack_builder *builder) {
+  return builder->transport;
+}
+
+const grpc_channel_args *grpc_channel_stack_builder_get_channel_arguments(
+    grpc_channel_stack_builder *builder) {
+  return builder->args;
+}
+
+bool grpc_channel_stack_builder_append_filter(
+    grpc_channel_stack_builder *builder, const grpc_channel_filter *filter,
+    grpc_post_filter_create_init_func post_init_func, void *user_data) {
+  grpc_channel_stack_builder_iterator *it =
+      grpc_channel_stack_builder_create_iterator_at_last(builder);
+  bool ok = grpc_channel_stack_builder_add_filter_before(
+      it, filter, post_init_func, user_data);
+  grpc_channel_stack_builder_iterator_destroy(it);
+  return ok;
+}
+
+bool grpc_channel_stack_builder_prepend_filter(
+    grpc_channel_stack_builder *builder, const grpc_channel_filter *filter,
+    grpc_post_filter_create_init_func post_init_func, void *user_data) {
+  grpc_channel_stack_builder_iterator *it =
+      grpc_channel_stack_builder_create_iterator_at_first(builder);
+  bool ok = grpc_channel_stack_builder_add_filter_after(
+      it, filter, post_init_func, user_data);
+  grpc_channel_stack_builder_iterator_destroy(it);
+  return ok;
+}
+
+static void add_after(filter_node *before, const grpc_channel_filter *filter,
+                      grpc_post_filter_create_init_func post_init_func,
+                      void *user_data) {
+  filter_node *new = gpr_malloc(sizeof(*new));
+  new->next = before->next;
+  new->prev = before;
+  new->next->prev = new->prev->next = new;
+  new->filter = filter;
+  new->init = post_init_func;
+  new->init_arg = user_data;
+}
+
+bool grpc_channel_stack_builder_add_filter_before(
+    grpc_channel_stack_builder_iterator *iterator,
+    const grpc_channel_filter *filter,
+    grpc_post_filter_create_init_func post_init_func, void *user_data) {
+  if (iterator->node == &iterator->builder->begin) return false;
+  add_after(iterator->node->prev, filter, post_init_func, user_data);
+  return true;
+}
+
+bool grpc_channel_stack_builder_add_filter_after(
+    grpc_channel_stack_builder_iterator *iterator,
+    const grpc_channel_filter *filter,
+    grpc_post_filter_create_init_func post_init_func, void *user_data) {
+  if (iterator->node == &iterator->builder->end) return false;
+  add_after(iterator->node, filter, post_init_func, user_data);
+  return true;
+}
+
+void grpc_channel_stack_builder_destroy(grpc_channel_stack_builder *builder) {
+  filter_node *p = builder->begin.next;
+  while (p != &builder->end) {
+    filter_node *next = p->next;
+    gpr_free(p);
+    p = next;
+  }
+  gpr_free(builder);
+}
+
+void *grpc_channel_stack_builder_finish(grpc_exec_ctx *exec_ctx,
+                                        grpc_channel_stack_builder *builder,
+                                        size_t prefix_bytes, int initial_refs,
+                                        grpc_iomgr_cb_func destroy,
+                                        void *destroy_arg) {
+  // count the number of filters
+  size_t num_filters = 0;
+  for (filter_node *p = builder->begin.next; p != &builder->end; p = p->next) {
+    num_filters++;
+  }
+
+  // create an array of filters
+  const grpc_channel_filter **filters =
+      gpr_malloc(sizeof(*filters) * num_filters);
+  size_t i = 0;
+  for (filter_node *p = builder->begin.next; p != &builder->end; p = p->next) {
+    filters[i++] = p->filter;
+  }
+
+  // calculate the size of the channel stack
+  size_t channel_stack_size = grpc_channel_stack_size(filters, num_filters);
+
+  // allocate memory, with prefix_bytes followed by channel_stack_size
+  char *result = gpr_malloc(prefix_bytes + channel_stack_size);
+  // fetch a pointer to the channel stack
+  grpc_channel_stack *channel_stack =
+      (grpc_channel_stack *)(result + prefix_bytes);
+  // and initialize it
+  grpc_channel_stack_init(exec_ctx, initial_refs, destroy,
+                          destroy_arg == NULL ? result : destroy_arg, filters,
+                          num_filters, builder->args, builder->name,
+                          channel_stack);
+
+  // run post-initialization functions
+  i = 0;
+  for (filter_node *p = builder->begin.next; p != &builder->end; p = p->next) {
+    if (p->init != NULL) {
+      p->init(channel_stack, grpc_channel_stack_element(channel_stack, i),
+              p->init_arg);
+    }
+    i++;
+  }
+
+  grpc_channel_stack_builder_destroy(builder);
+  gpr_free((grpc_channel_filter **)filters);
+
+  return result;
+}
diff --git a/src/core/lib/channel/channel_stack_builder.h b/src/core/lib/channel/channel_stack_builder.h
new file mode 100644
index 0000000000..15f395e8b8
--- /dev/null
+++ b/src/core/lib/channel/channel_stack_builder.h
@@ -0,0 +1,155 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_CHANNEL_CHANNEL_STACK_BUILDER_H
+#define GRPC_CORE_CHANNEL_CHANNEL_STACK_BUILDER_H
+
+#include <stdbool.h>
+
+#include "src/core/channel/channel_args.h"
+#include "src/core/channel/channel_stack.h"
+
+/// grpc_channel_stack_builder offers a programmatic interface to selected
+/// and order channel filters
+typedef struct grpc_channel_stack_builder grpc_channel_stack_builder;
+typedef struct grpc_channel_stack_builder_iterator
+    grpc_channel_stack_builder_iterator;
+
+/// Create a new channel stack builder
+grpc_channel_stack_builder *grpc_channel_stack_builder_create(void);
+
+/// Assign a name to the channel stack: \a name must be statically allocated
+void grpc_channel_stack_builder_set_name(grpc_channel_stack_builder *builder,
+                                         const char *name);
+
+/// Attach \a transport to the builder (does not take ownership)
+void grpc_channel_stack_builder_set_transport(
+    grpc_channel_stack_builder *builder, grpc_transport *transport);
+
+/// Fetch attached transport
+grpc_transport *grpc_channel_stack_builder_get_transport(
+    grpc_channel_stack_builder *builder);
+
+/// Set channel arguments: \a args must continue to exist until after
+/// grpc_channel_stack_builder_finish returns
+void grpc_channel_stack_builder_set_channel_arguments(
+    grpc_channel_stack_builder *builder, const grpc_channel_args *args);
+
+/// Return a borrowed pointer to the channel arguments
+const grpc_channel_args *grpc_channel_stack_builder_get_channel_arguments(
+    grpc_channel_stack_builder *builder);
+
+/// Begin iterating over already defined filters in the builder at the beginning
+grpc_channel_stack_builder_iterator *
+grpc_channel_stack_builder_create_iterator_at_first(
+    grpc_channel_stack_builder *builder);
+
+/// Begin iterating over already defined filters in the builder at the end
+grpc_channel_stack_builder_iterator *
+grpc_channel_stack_builder_create_iterator_at_last(
+    grpc_channel_stack_builder *builder);
+
+/// Is an iterator at the first element?
+bool grpc_channel_stack_builder_iterator_is_first(
+    grpc_channel_stack_builder_iterator *iterator);
+
+/// Is an iterator at the end?
+bool grpc_channel_stack_builder_iterator_is_end(
+    grpc_channel_stack_builder_iterator *iterator);
+
+/// Move an iterator to the next item
+bool grpc_channel_stack_builder_move_next(
+    grpc_channel_stack_builder_iterator *iterator);
+
+/// Move an iterator to the previous item
+bool grpc_channel_stack_builder_move_prev(
+    grpc_channel_stack_builder_iterator *iterator);
+
+typedef void (*grpc_post_filter_create_init_func)(
+    grpc_channel_stack *channel_stack, grpc_channel_element *elem, void *arg);
+
+/// Add \a filter to the stack, after \a iterator.
+/// Call \a post_init_func(..., \a user_data) once the channel stack is
+/// created.
+bool grpc_channel_stack_builder_add_filter_after(
+    grpc_channel_stack_builder_iterator *iterator,
+    const grpc_channel_filter *filter,
+    grpc_post_filter_create_init_func post_init_func,
+    void *user_data) GRPC_MUST_USE_RESULT;
+
+/// Add \a filter to the stack, before \a iterator.
+/// Call \a post_init_func(..., \a user_data) once the channel stack is
+/// created.
+bool grpc_channel_stack_builder_add_filter_before(
+    grpc_channel_stack_builder_iterator *iterator,
+    const grpc_channel_filter *filter,
+    grpc_post_filter_create_init_func post_init_func,
+    void *user_data) GRPC_MUST_USE_RESULT;
+
+/// Add \a filter to the beginning of the filter list.
+/// Call \a post_init_func(..., \a user_data) once the channel stack is
+/// created.
+bool grpc_channel_stack_builder_prepend_filter(
+    grpc_channel_stack_builder *builder, const grpc_channel_filter *filter,
+    grpc_post_filter_create_init_func post_init_func,
+    void *user_data) GRPC_MUST_USE_RESULT;
+
+/// Add \a filter to the end of the filter list.
+/// Call \a post_init_func(..., \a user_data) once the channel stack is
+/// created.
+bool grpc_channel_stack_builder_append_filter(
+    grpc_channel_stack_builder *builder, const grpc_channel_filter *filter,
+    grpc_post_filter_create_init_func post_init_func,
+    void *user_data) GRPC_MUST_USE_RESULT;
+
+/// Terminate iteration and destroy \a iterator
+void grpc_channel_stack_builder_iterator_destroy(
+    grpc_channel_stack_builder_iterator *iterator);
+
+/// Destroy the builder, return the freshly minted channel stack
+/// Allocates \a prefix_bytes bytes before the channel stack
+/// Returns the base pointer of the allocated block
+/// \a initial_refs, \a destroy, \a destroy_arg are as per
+/// grpc_channel_stack_init
+void *grpc_channel_stack_builder_finish(grpc_exec_ctx *exec_ctx,
+                                        grpc_channel_stack_builder *builder,
+                                        size_t prefix_bytes, int initial_refs,
+                                        grpc_iomgr_cb_func destroy,
+                                        void *destroy_arg);
+
+/// Destroy the builder without creating a channel stack
+void grpc_channel_stack_builder_destroy(grpc_channel_stack_builder *builder);
+
+extern int grpc_trace_channel_stack_builder;
+
+#endif /* GRPC_CORE_CHANNEL_CHANNEL_STACK_BUILDER_H */
diff --git a/src/core/lib/channel/client_channel.c b/src/core/lib/channel/client_channel.c
new file mode 100644
index 0000000000..ad1ded9ab7
--- /dev/null
+++ b/src/core/lib/channel/client_channel.c
@@ -0,0 +1,526 @@
+/*
+ *
+ * Copyright 2015-2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/channel/client_channel.h"
+
+#include <stdio.h>
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+#include <grpc/support/sync.h>
+#include <grpc/support/useful.h>
+
+#include "src/core/channel/channel_args.h"
+#include "src/core/channel/connected_channel.h"
+#include "src/core/channel/subchannel_call_holder.h"
+#include "src/core/iomgr/iomgr.h"
+#include "src/core/profiling/timers.h"
+#include "src/core/support/string.h"
+#include "src/core/surface/channel.h"
+#include "src/core/transport/connectivity_state.h"
+
+/* Client channel implementation */
+
+typedef grpc_subchannel_call_holder call_data;
+
+typedef struct client_channel_channel_data {
+  /** resolver for this channel */
+  grpc_resolver *resolver;
+  /** have we started resolving this channel */
+  int started_resolving;
+
+  /** mutex protecting client configuration, including all
+      variables below in this data structure */
+  gpr_mu mu_config;
+  /** currently active load balancer - guarded by mu_config */
+  grpc_lb_policy *lb_policy;
+  /** incoming configuration - set by resolver.next
+      guarded by mu_config */
+  grpc_client_config *incoming_configuration;
+  /** a list of closures that are all waiting for config to come in */
+  grpc_closure_list waiting_for_config_closures;
+  /** resolver callback */
+  grpc_closure on_config_changed;
+  /** connectivity state being tracked */
+  grpc_connectivity_state_tracker state_tracker;
+  /** when an lb_policy arrives, should we try to exit idle */
+  int exit_idle_when_lb_policy_arrives;
+  /** owning stack */
+  grpc_channel_stack *owning_stack;
+  /** interested parties (owned) */
+  grpc_pollset_set *interested_parties;
+} channel_data;
+
+/** We create one watcher for each new lb_policy that is returned from a
+   resolver,
+    to watch for state changes from the lb_policy. When a state change is seen,
+   we
+    update the channel, and create a new watcher */
+typedef struct {
+  channel_data *chand;
+  grpc_closure on_changed;
+  grpc_connectivity_state state;
+  grpc_lb_policy *lb_policy;
+} lb_policy_connectivity_watcher;
+
+typedef struct {
+  grpc_closure closure;
+  grpc_call_element *elem;
+} waiting_call;
+
+static char *cc_get_peer(grpc_exec_ctx *exec_ctx, grpc_call_element *elem) {
+  return grpc_subchannel_call_holder_get_peer(exec_ctx, elem->call_data);
+}
+
+static void cc_start_transport_stream_op(grpc_exec_ctx *exec_ctx,
+                                         grpc_call_element *elem,
+                                         grpc_transport_stream_op *op) {
+  GRPC_CALL_LOG_OP(GPR_INFO, elem, op);
+  grpc_subchannel_call_holder_perform_op(exec_ctx, elem->call_data, op);
+}
+
+static void watch_lb_policy(grpc_exec_ctx *exec_ctx, channel_data *chand,
+                            grpc_lb_policy *lb_policy,
+                            grpc_connectivity_state current_state);
+
+static void on_lb_policy_state_changed_locked(
+    grpc_exec_ctx *exec_ctx, lb_policy_connectivity_watcher *w) {
+  grpc_connectivity_state publish_state = w->state;
+  /* check if the notification is for a stale policy */
+  if (w->lb_policy != w->chand->lb_policy) return;
+
+  if (publish_state == GRPC_CHANNEL_FATAL_FAILURE &&
+      w->chand->resolver != NULL) {
+    publish_state = GRPC_CHANNEL_TRANSIENT_FAILURE;
+    grpc_resolver_channel_saw_error(exec_ctx, w->chand->resolver);
+    GRPC_LB_POLICY_UNREF(exec_ctx, w->chand->lb_policy, "channel");
+    w->chand->lb_policy = NULL;
+  }
+  grpc_connectivity_state_set(exec_ctx, &w->chand->state_tracker, publish_state,
+                              "lb_changed");
+  if (w->state != GRPC_CHANNEL_FATAL_FAILURE) {
+    watch_lb_policy(exec_ctx, w->chand, w->lb_policy, w->state);
+  }
+}
+
+static void on_lb_policy_state_changed(grpc_exec_ctx *exec_ctx, void *arg,
+                                       bool iomgr_success) {
+  lb_policy_connectivity_watcher *w = arg;
+
+  gpr_mu_lock(&w->chand->mu_config);
+  on_lb_policy_state_changed_locked(exec_ctx, w);
+  gpr_mu_unlock(&w->chand->mu_config);
+
+  GRPC_CHANNEL_STACK_UNREF(exec_ctx, w->chand->owning_stack, "watch_lb_policy");
+  gpr_free(w);
+}
+
+static void watch_lb_policy(grpc_exec_ctx *exec_ctx, channel_data *chand,
+                            grpc_lb_policy *lb_policy,
+                            grpc_connectivity_state current_state) {
+  lb_policy_connectivity_watcher *w = gpr_malloc(sizeof(*w));
+  GRPC_CHANNEL_STACK_REF(chand->owning_stack, "watch_lb_policy");
+
+  w->chand = chand;
+  grpc_closure_init(&w->on_changed, on_lb_policy_state_changed, w);
+  w->state = current_state;
+  w->lb_policy = lb_policy;
+  grpc_lb_policy_notify_on_state_change(exec_ctx, lb_policy, &w->state,
+                                        &w->on_changed);
+}
+
+static void cc_on_config_changed(grpc_exec_ctx *exec_ctx, void *arg,
+                                 bool iomgr_success) {
+  channel_data *chand = arg;
+  grpc_lb_policy *lb_policy = NULL;
+  grpc_lb_policy *old_lb_policy;
+  grpc_connectivity_state state = GRPC_CHANNEL_TRANSIENT_FAILURE;
+  int exit_idle = 0;
+
+  if (chand->incoming_configuration != NULL) {
+    lb_policy = grpc_client_config_get_lb_policy(chand->incoming_configuration);
+    if (lb_policy != NULL) {
+      GRPC_LB_POLICY_REF(lb_policy, "channel");
+      GRPC_LB_POLICY_REF(lb_policy, "config_change");
+      state = grpc_lb_policy_check_connectivity(exec_ctx, lb_policy);
+    }
+
+    grpc_client_config_unref(exec_ctx, chand->incoming_configuration);
+  }
+
+  chand->incoming_configuration = NULL;
+
+  if (lb_policy != NULL) {
+    grpc_pollset_set_add_pollset_set(exec_ctx, lb_policy->interested_parties,
+                                     chand->interested_parties);
+  }
+
+  gpr_mu_lock(&chand->mu_config);
+  old_lb_policy = chand->lb_policy;
+  chand->lb_policy = lb_policy;
+  if (lb_policy != NULL || chand->resolver == NULL /* disconnected */) {
+    grpc_exec_ctx_enqueue_list(exec_ctx, &chand->waiting_for_config_closures,
+                               NULL);
+  }
+  if (lb_policy != NULL && chand->exit_idle_when_lb_policy_arrives) {
+    GRPC_LB_POLICY_REF(lb_policy, "exit_idle");
+    exit_idle = 1;
+    chand->exit_idle_when_lb_policy_arrives = 0;
+  }
+
+  if (iomgr_success && chand->resolver) {
+    grpc_connectivity_state_set(exec_ctx, &chand->state_tracker, state,
+                                "new_lb+resolver");
+    if (lb_policy != NULL) {
+      watch_lb_policy(exec_ctx, chand, lb_policy, state);
+    }
+    GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
+    grpc_resolver_next(exec_ctx, chand->resolver,
+                       &chand->incoming_configuration,
+                       &chand->on_config_changed);
+    gpr_mu_unlock(&chand->mu_config);
+  } else {
+    if (chand->resolver != NULL) {
+      grpc_resolver_shutdown(exec_ctx, chand->resolver);
+      GRPC_RESOLVER_UNREF(exec_ctx, chand->resolver, "channel");
+      chand->resolver = NULL;
+    }
+    grpc_connectivity_state_set(exec_ctx, &chand->state_tracker,
+                                GRPC_CHANNEL_FATAL_FAILURE, "resolver_gone");
+    gpr_mu_unlock(&chand->mu_config);
+  }
+
+  if (exit_idle) {
+    grpc_lb_policy_exit_idle(exec_ctx, lb_policy);
+    GRPC_LB_POLICY_UNREF(exec_ctx, lb_policy, "exit_idle");
+  }
+
+  if (old_lb_policy != NULL) {
+    grpc_pollset_set_del_pollset_set(
+        exec_ctx, old_lb_policy->interested_parties, chand->interested_parties);
+    GRPC_LB_POLICY_UNREF(exec_ctx, old_lb_policy, "channel");
+  }
+
+  if (lb_policy != NULL) {
+    GRPC_LB_POLICY_UNREF(exec_ctx, lb_policy, "config_change");
+  }
+
+  GRPC_CHANNEL_STACK_UNREF(exec_ctx, chand->owning_stack, "resolver");
+}
+
+static void cc_start_transport_op(grpc_exec_ctx *exec_ctx,
+                                  grpc_channel_element *elem,
+                                  grpc_transport_op *op) {
+  channel_data *chand = elem->channel_data;
+
+  grpc_exec_ctx_enqueue(exec_ctx, op->on_consumed, true, NULL);
+
+  GPR_ASSERT(op->set_accept_stream == false);
+  if (op->bind_pollset != NULL) {
+    grpc_pollset_set_add_pollset(exec_ctx, chand->interested_parties,
+                                 op->bind_pollset);
+  }
+
+  gpr_mu_lock(&chand->mu_config);
+  if (op->on_connectivity_state_change != NULL) {
+    grpc_connectivity_state_notify_on_state_change(
+        exec_ctx, &chand->state_tracker, op->connectivity_state,
+        op->on_connectivity_state_change);
+    op->on_connectivity_state_change = NULL;
+    op->connectivity_state = NULL;
+  }
+
+  if (op->send_ping != NULL) {
+    if (chand->lb_policy == NULL) {
+      grpc_exec_ctx_enqueue(exec_ctx, op->send_ping, false, NULL);
+    } else {
+      grpc_lb_policy_ping_one(exec_ctx, chand->lb_policy, op->send_ping);
+      op->bind_pollset = NULL;
+    }
+    op->send_ping = NULL;
+  }
+
+  if (op->disconnect && chand->resolver != NULL) {
+    grpc_connectivity_state_set(exec_ctx, &chand->state_tracker,
+                                GRPC_CHANNEL_FATAL_FAILURE, "disconnect");
+    grpc_resolver_shutdown(exec_ctx, chand->resolver);
+    GRPC_RESOLVER_UNREF(exec_ctx, chand->resolver, "channel");
+    chand->resolver = NULL;
+    if (chand->lb_policy != NULL) {
+      grpc_pollset_set_del_pollset_set(exec_ctx,
+                                       chand->lb_policy->interested_parties,
+                                       chand->interested_parties);
+      GRPC_LB_POLICY_UNREF(exec_ctx, chand->lb_policy, "channel");
+      chand->lb_policy = NULL;
+    }
+  }
+  gpr_mu_unlock(&chand->mu_config);
+}
+
+typedef struct {
+  grpc_metadata_batch *initial_metadata;
+  grpc_connected_subchannel **connected_subchannel;
+  grpc_closure *on_ready;
+  grpc_call_element *elem;
+  grpc_closure closure;
+} continue_picking_args;
+
+static int cc_pick_subchannel(grpc_exec_ctx *exec_ctx, void *arg,
+                              grpc_metadata_batch *initial_metadata,
+                              grpc_connected_subchannel **connected_subchannel,
+                              grpc_closure *on_ready);
+
+static void continue_picking(grpc_exec_ctx *exec_ctx, void *arg, bool success) {
+  continue_picking_args *cpa = arg;
+  if (!success) {
+    grpc_exec_ctx_enqueue(exec_ctx, cpa->on_ready, false, NULL);
+  } else if (cpa->connected_subchannel == NULL) {
+    /* cancelled, do nothing */
+  } else if (cc_pick_subchannel(exec_ctx, cpa->elem, cpa->initial_metadata,
+                                cpa->connected_subchannel, cpa->on_ready)) {
+    grpc_exec_ctx_enqueue(exec_ctx, cpa->on_ready, true, NULL);
+  }
+  gpr_free(cpa);
+}
+
+static int cc_pick_subchannel(grpc_exec_ctx *exec_ctx, void *elemp,
+                              grpc_metadata_batch *initial_metadata,
+                              grpc_connected_subchannel **connected_subchannel,
+                              grpc_closure *on_ready) {
+  grpc_call_element *elem = elemp;
+  channel_data *chand = elem->channel_data;
+  call_data *calld = elem->call_data;
+  continue_picking_args *cpa;
+  grpc_closure *closure;
+
+  GPR_ASSERT(connected_subchannel);
+
+  gpr_mu_lock(&chand->mu_config);
+  if (initial_metadata == NULL) {
+    if (chand->lb_policy != NULL) {
+      grpc_lb_policy_cancel_pick(exec_ctx, chand->lb_policy,
+                                 connected_subchannel);
+    }
+    for (closure = chand->waiting_for_config_closures.head; closure != NULL;
+         closure = grpc_closure_next(closure)) {
+      cpa = closure->cb_arg;
+      if (cpa->connected_subchannel == connected_subchannel) {
+        cpa->connected_subchannel = NULL;
+        grpc_exec_ctx_enqueue(exec_ctx, cpa->on_ready, false, NULL);
+      }
+    }
+    gpr_mu_unlock(&chand->mu_config);
+    return 1;
+  }
+  if (chand->lb_policy != NULL) {
+    grpc_lb_policy *lb_policy = chand->lb_policy;
+    int r;
+    GRPC_LB_POLICY_REF(lb_policy, "cc_pick_subchannel");
+    gpr_mu_unlock(&chand->mu_config);
+    r = grpc_lb_policy_pick(exec_ctx, lb_policy, calld->pollset,
+                            initial_metadata, connected_subchannel, on_ready);
+    GRPC_LB_POLICY_UNREF(exec_ctx, lb_policy, "cc_pick_subchannel");
+    return r;
+  }
+  if (chand->resolver != NULL && !chand->started_resolving) {
+    chand->started_resolving = 1;
+    GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
+    grpc_resolver_next(exec_ctx, chand->resolver,
+                       &chand->incoming_configuration,
+                       &chand->on_config_changed);
+  }
+  cpa = gpr_malloc(sizeof(*cpa));
+  cpa->initial_metadata = initial_metadata;
+  cpa->connected_subchannel = connected_subchannel;
+  cpa->on_ready = on_ready;
+  cpa->elem = elem;
+  grpc_closure_init(&cpa->closure, continue_picking, cpa);
+  grpc_closure_list_add(&chand->waiting_for_config_closures, &cpa->closure, 1);
+  gpr_mu_unlock(&chand->mu_config);
+  return 0;
+}
+
+/* Constructor for call_data */
+static void init_call_elem(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
+                           grpc_call_element_args *args) {
+  grpc_subchannel_call_holder_init(elem->call_data, cc_pick_subchannel, elem,
+                                   args->call_stack);
+}
+
+/* Destructor for call_data */
+static void destroy_call_elem(grpc_exec_ctx *exec_ctx,
+                              grpc_call_element *elem) {
+  grpc_subchannel_call_holder_destroy(exec_ctx, elem->call_data);
+}
+
+/* Constructor for channel_data */
+static void init_channel_elem(grpc_exec_ctx *exec_ctx,
+                              grpc_channel_element *elem,
+                              grpc_channel_element_args *args) {
+  channel_data *chand = elem->channel_data;
+
+  memset(chand, 0, sizeof(*chand));
+
+  GPR_ASSERT(args->is_last);
+  GPR_ASSERT(elem->filter == &grpc_client_channel_filter);
+
+  gpr_mu_init(&chand->mu_config);
+  grpc_closure_init(&chand->on_config_changed, cc_on_config_changed, chand);
+  chand->owning_stack = args->channel_stack;
+
+  grpc_connectivity_state_init(&chand->state_tracker, GRPC_CHANNEL_IDLE,
+                               "client_channel");
+  chand->interested_parties = grpc_pollset_set_create();
+}
+
+/* Destructor for channel_data */
+static void destroy_channel_elem(grpc_exec_ctx *exec_ctx,
+                                 grpc_channel_element *elem) {
+  channel_data *chand = elem->channel_data;
+
+  if (chand->resolver != NULL) {
+    grpc_resolver_shutdown(exec_ctx, chand->resolver);
+    GRPC_RESOLVER_UNREF(exec_ctx, chand->resolver, "channel");
+  }
+  if (chand->lb_policy != NULL) {
+    grpc_pollset_set_del_pollset_set(exec_ctx,
+                                     chand->lb_policy->interested_parties,
+                                     chand->interested_parties);
+    GRPC_LB_POLICY_UNREF(exec_ctx, chand->lb_policy, "channel");
+  }
+  grpc_connectivity_state_destroy(exec_ctx, &chand->state_tracker);
+  grpc_pollset_set_destroy(chand->interested_parties);
+  gpr_mu_destroy(&chand->mu_config);
+}
+
+static void cc_set_pollset(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
+                           grpc_pollset *pollset) {
+  call_data *calld = elem->call_data;
+  calld->pollset = pollset;
+}
+
+const grpc_channel_filter grpc_client_channel_filter = {
+    cc_start_transport_stream_op,
+    cc_start_transport_op,
+    sizeof(call_data),
+    init_call_elem,
+    cc_set_pollset,
+    destroy_call_elem,
+    sizeof(channel_data),
+    init_channel_elem,
+    destroy_channel_elem,
+    cc_get_peer,
+    "client-channel",
+};
+
+void grpc_client_channel_set_resolver(grpc_exec_ctx *exec_ctx,
+                                      grpc_channel_stack *channel_stack,
+                                      grpc_resolver *resolver) {
+  /* post construction initialization: set the transport setup pointer */
+  grpc_channel_element *elem = grpc_channel_stack_last_element(channel_stack);
+  channel_data *chand = elem->channel_data;
+  gpr_mu_lock(&chand->mu_config);
+  GPR_ASSERT(!chand->resolver);
+  chand->resolver = resolver;
+  GRPC_RESOLVER_REF(resolver, "channel");
+  if (!grpc_closure_list_empty(chand->waiting_for_config_closures) ||
+      chand->exit_idle_when_lb_policy_arrives) {
+    chand->started_resolving = 1;
+    GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
+    grpc_resolver_next(exec_ctx, resolver, &chand->incoming_configuration,
+                       &chand->on_config_changed);
+  }
+  gpr_mu_unlock(&chand->mu_config);
+}
+
+grpc_connectivity_state grpc_client_channel_check_connectivity_state(
+    grpc_exec_ctx *exec_ctx, grpc_channel_element *elem, int try_to_connect) {
+  channel_data *chand = elem->channel_data;
+  grpc_connectivity_state out;
+  gpr_mu_lock(&chand->mu_config);
+  out = grpc_connectivity_state_check(&chand->state_tracker);
+  if (out == GRPC_CHANNEL_IDLE && try_to_connect) {
+    if (chand->lb_policy != NULL) {
+      grpc_lb_policy_exit_idle(exec_ctx, chand->lb_policy);
+    } else {
+      chand->exit_idle_when_lb_policy_arrives = 1;
+      if (!chand->started_resolving && chand->resolver != NULL) {
+        GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
+        chand->started_resolving = 1;
+        grpc_resolver_next(exec_ctx, chand->resolver,
+                           &chand->incoming_configuration,
+                           &chand->on_config_changed);
+      }
+    }
+  }
+  gpr_mu_unlock(&chand->mu_config);
+  return out;
+}
+
+typedef struct {
+  channel_data *chand;
+  grpc_pollset *pollset;
+  grpc_closure *on_complete;
+  grpc_closure my_closure;
+} external_connectivity_watcher;
+
+static void on_external_watch_complete(grpc_exec_ctx *exec_ctx, void *arg,
+                                       bool iomgr_success) {
+  external_connectivity_watcher *w = arg;
+  grpc_closure *follow_up = w->on_complete;
+  grpc_pollset_set_del_pollset(exec_ctx, w->chand->interested_parties,
+                               w->pollset);
+  GRPC_CHANNEL_STACK_UNREF(exec_ctx, w->chand->owning_stack,
+                           "external_connectivity_watcher");
+  gpr_free(w);
+  follow_up->cb(exec_ctx, follow_up->cb_arg, iomgr_success);
+}
+
+void grpc_client_channel_watch_connectivity_state(
+    grpc_exec_ctx *exec_ctx, grpc_channel_element *elem, grpc_pollset *pollset,
+    grpc_connectivity_state *state, grpc_closure *on_complete) {
+  channel_data *chand = elem->channel_data;
+  external_connectivity_watcher *w = gpr_malloc(sizeof(*w));
+  w->chand = chand;
+  w->pollset = pollset;
+  w->on_complete = on_complete;
+  grpc_pollset_set_add_pollset(exec_ctx, chand->interested_parties, pollset);
+  grpc_closure_init(&w->my_closure, on_external_watch_complete, w);
+  GRPC_CHANNEL_STACK_REF(w->chand->owning_stack,
+                         "external_connectivity_watcher");
+  gpr_mu_lock(&chand->mu_config);
+  grpc_connectivity_state_notify_on_state_change(
+      exec_ctx, &chand->state_tracker, state, &w->my_closure);
+  gpr_mu_unlock(&chand->mu_config);
+}
diff --git a/src/core/lib/channel/client_channel.h b/src/core/lib/channel/client_channel.h
new file mode 100644
index 0000000000..422f7f8374
--- /dev/null
+++ b/src/core/lib/channel/client_channel.h
@@ -0,0 +1,63 @@
+/*
+ *
+ * Copyright 2015-2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_CHANNEL_CLIENT_CHANNEL_H
+#define GRPC_CORE_CHANNEL_CLIENT_CHANNEL_H
+
+#include "src/core/channel/channel_stack.h"
+#include "src/core/client_config/resolver.h"
+
+/* A client channel is a channel that begins disconnected, and can connect
+   to some endpoint on demand. If that endpoint disconnects, it will be
+   connected to again later.
+
+   Calls on a disconnected client channel are queued until a connection is
+   established. */
+
+extern const grpc_channel_filter grpc_client_channel_filter;
+
+/* post-construction initializer to let the client channel know which
+   transport setup it should cancel upon destruction, or initiate when it needs
+   a connection */
+void grpc_client_channel_set_resolver(grpc_exec_ctx *exec_ctx,
+                                      grpc_channel_stack *channel_stack,
+                                      grpc_resolver *resolver);
+
+grpc_connectivity_state grpc_client_channel_check_connectivity_state(
+    grpc_exec_ctx *exec_ctx, grpc_channel_element *elem, int try_to_connect);
+
+void grpc_client_channel_watch_connectivity_state(
+    grpc_exec_ctx *exec_ctx, grpc_channel_element *elem, grpc_pollset *pollset,
+    grpc_connectivity_state *state, grpc_closure *on_complete);
+
+#endif /* GRPC_CORE_CHANNEL_CLIENT_CHANNEL_H */
diff --git a/src/core/lib/channel/compress_filter.c b/src/core/lib/channel/compress_filter.c
new file mode 100644
index 0000000000..6f5a9740ad
--- /dev/null
+++ b/src/core/lib/channel/compress_filter.c
@@ -0,0 +1,304 @@
+/*
+ *
+ * Copyright 2015-2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include <assert.h>
+#include <string.h>
+
+#include <grpc/compression.h>
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+#include <grpc/support/slice_buffer.h>
+
+#include "src/core/channel/channel_args.h"
+#include "src/core/channel/compress_filter.h"
+#include "src/core/compression/algorithm_metadata.h"
+#include "src/core/compression/message_compress.h"
+#include "src/core/profiling/timers.h"
+#include "src/core/support/string.h"
+#include "src/core/transport/static_metadata.h"
+
+typedef struct call_data {
+  gpr_slice_buffer slices; /**< Buffers up input slices to be compressed */
+  grpc_linked_mdelem compression_algorithm_storage;
+  grpc_linked_mdelem accept_encoding_storage;
+  uint32_t remaining_slice_bytes;
+  /** Compression algorithm we'll try to use. It may be given by incoming
+   * metadata, or by the channel's default compression settings. */
+  grpc_compression_algorithm compression_algorithm;
+  /** If true, contents of \a compression_algorithm are authoritative */
+  int has_compression_algorithm;
+
+  grpc_transport_stream_op send_op;
+  uint32_t send_length;
+  uint32_t send_flags;
+  gpr_slice incoming_slice;
+  grpc_slice_buffer_stream replacement_stream;
+  grpc_closure *post_send;
+  grpc_closure send_done;
+  grpc_closure got_slice;
+} call_data;
+
+typedef struct channel_data {
+  /** The default, channel-level, compression algorithm */
+  grpc_compression_algorithm default_compression_algorithm;
+  /** Compression options for the channel */
+  grpc_compression_options compression_options;
+  /** Supported compression algorithms */
+  uint32_t supported_compression_algorithms;
+} channel_data;
+
+/** For each \a md element from the incoming metadata, filter out the entry for
+ * "grpc-encoding", using its value to populate the call data's
+ * compression_algorithm field. */
+static grpc_mdelem *compression_md_filter(void *user_data, grpc_mdelem *md) {
+  grpc_call_element *elem = user_data;
+  call_data *calld = elem->call_data;
+  channel_data *channeld = elem->channel_data;
+
+  if (md->key == GRPC_MDSTR_GRPC_INTERNAL_ENCODING_REQUEST) {
+    const char *md_c_str = grpc_mdstr_as_c_string(md->value);
+    if (!grpc_compression_algorithm_parse(md_c_str, strlen(md_c_str),
+                                          &calld->compression_algorithm)) {
+      gpr_log(GPR_ERROR,
+              "Invalid compression algorithm: '%s' (unknown). Ignoring.",
+              md_c_str);
+      calld->compression_algorithm = GRPC_COMPRESS_NONE;
+    }
+    if (grpc_compression_options_is_algorithm_enabled(
+            &channeld->compression_options, calld->compression_algorithm) ==
+        0) {
+      gpr_log(GPR_ERROR,
+              "Invalid compression algorithm: '%s' (previously disabled). "
+              "Ignoring.",
+              md_c_str);
+      calld->compression_algorithm = GRPC_COMPRESS_NONE;
+    }
+    calld->has_compression_algorithm = 1;
+    return NULL;
+  }
+
+  return md;
+}
+
+static int skip_compression(grpc_call_element *elem) {
+  call_data *calld = elem->call_data;
+  channel_data *channeld = elem->channel_data;
+  if (calld->has_compression_algorithm) {
+    if (calld->compression_algorithm == GRPC_COMPRESS_NONE) {
+      return 1;
+    }
+    return 0; /* we have an actual call-specific algorithm */
+  }
+  /* no per-call compression override */
+  return channeld->default_compression_algorithm == GRPC_COMPRESS_NONE;
+}
+
+/** Filter initial metadata */
+static void process_send_initial_metadata(
+    grpc_call_element *elem, grpc_metadata_batch *initial_metadata) {
+  call_data *calld = elem->call_data;
+  channel_data *channeld = elem->channel_data;
+  /* Parse incoming request for compression. If any, it'll be available
+   * at calld->compression_algorithm */
+  grpc_metadata_batch_filter(initial_metadata, compression_md_filter, elem);
+  if (!calld->has_compression_algorithm) {
+    /* If no algorithm was found in the metadata and we aren't
+     * exceptionally skipping compression, fall back to the channel
+     * default */
+    calld->compression_algorithm = channeld->default_compression_algorithm;
+    calld->has_compression_algorithm = 1; /* GPR_TRUE */
+  }
+  /* hint compression algorithm */
+  grpc_metadata_batch_add_tail(
+      initial_metadata, &calld->compression_algorithm_storage,
+      grpc_compression_encoding_mdelem(calld->compression_algorithm));
+
+  /* convey supported compression algorithms */
+  grpc_metadata_batch_add_tail(initial_metadata,
+                               &calld->accept_encoding_storage,
+                               GRPC_MDELEM_ACCEPT_ENCODING_FOR_ALGORITHMS(
+                                   channeld->supported_compression_algorithms));
+}
+
+static void continue_send_message(grpc_exec_ctx *exec_ctx,
+                                  grpc_call_element *elem);
+
+static void send_done(grpc_exec_ctx *exec_ctx, void *elemp, bool success) {
+  grpc_call_element *elem = elemp;
+  call_data *calld = elem->call_data;
+  gpr_slice_buffer_reset_and_unref(&calld->slices);
+  calld->post_send->cb(exec_ctx, calld->post_send->cb_arg, success);
+}
+
+static void finish_send_message(grpc_exec_ctx *exec_ctx,
+                                grpc_call_element *elem) {
+  call_data *calld = elem->call_data;
+  int did_compress;
+  gpr_slice_buffer tmp;
+  gpr_slice_buffer_init(&tmp);
+  did_compress =
+      grpc_msg_compress(calld->compression_algorithm, &calld->slices, &tmp);
+  if (did_compress) {
+    gpr_slice_buffer_swap(&calld->slices, &tmp);
+    calld->send_flags |= GRPC_WRITE_INTERNAL_COMPRESS;
+  }
+  gpr_slice_buffer_destroy(&tmp);
+
+  grpc_slice_buffer_stream_init(&calld->replacement_stream, &calld->slices,
+                                calld->send_flags);
+  calld->send_op.send_message = &calld->replacement_stream.base;
+  calld->post_send = calld->send_op.on_complete;
+  calld->send_op.on_complete = &calld->send_done;
+
+  grpc_call_next_op(exec_ctx, elem, &calld->send_op);
+}
+
+static void got_slice(grpc_exec_ctx *exec_ctx, void *elemp, bool success) {
+  grpc_call_element *elem = elemp;
+  call_data *calld = elem->call_data;
+  gpr_slice_buffer_add(&calld->slices, calld->incoming_slice);
+  if (calld->send_length == calld->slices.length) {
+    finish_send_message(exec_ctx, elem);
+  } else {
+    continue_send_message(exec_ctx, elem);
+  }
+}
+
+static void continue_send_message(grpc_exec_ctx *exec_ctx,
+                                  grpc_call_element *elem) {
+  call_data *calld = elem->call_data;
+  while (grpc_byte_stream_next(exec_ctx, calld->send_op.send_message,
+                               &calld->incoming_slice, ~(size_t)0,
+                               &calld->got_slice)) {
+    gpr_slice_buffer_add(&calld->slices, calld->incoming_slice);
+    if (calld->send_length == calld->slices.length) {
+      finish_send_message(exec_ctx, elem);
+      break;
+    }
+  }
+}
+
+static void compress_start_transport_stream_op(grpc_exec_ctx *exec_ctx,
+                                               grpc_call_element *elem,
+                                               grpc_transport_stream_op *op) {
+  call_data *calld = elem->call_data;
+
+  GPR_TIMER_BEGIN("compress_start_transport_stream_op", 0);
+
+  if (op->send_initial_metadata) {
+    process_send_initial_metadata(elem, op->send_initial_metadata);
+  }
+  if (op->send_message != NULL && !skip_compression(elem) &&
+      0 == (op->send_message->flags & GRPC_WRITE_NO_COMPRESS)) {
+    calld->send_op = *op;
+    calld->send_length = op->send_message->length;
+    calld->send_flags = op->send_message->flags;
+    continue_send_message(exec_ctx, elem);
+  } else {
+    /* pass control down the stack */
+    grpc_call_next_op(exec_ctx, elem, op);
+  }
+
+  GPR_TIMER_END("compress_start_transport_stream_op", 0);
+}
+
+/* Constructor for call_data */
+static void init_call_elem(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
+                           grpc_call_element_args *args) {
+  /* grab pointers to our data from the call element */
+  call_data *calld = elem->call_data;
+
+  /* initialize members */
+  gpr_slice_buffer_init(&calld->slices);
+  calld->has_compression_algorithm = 0;
+  grpc_closure_init(&calld->got_slice, got_slice, elem);
+  grpc_closure_init(&calld->send_done, send_done, elem);
+}
+
+/* Destructor for call_data */
+static void destroy_call_elem(grpc_exec_ctx *exec_ctx,
+                              grpc_call_element *elem) {
+  /* grab pointers to our data from the call element */
+  call_data *calld = elem->call_data;
+  gpr_slice_buffer_destroy(&calld->slices);
+}
+
+/* Constructor for channel_data */
+static void init_channel_elem(grpc_exec_ctx *exec_ctx,
+                              grpc_channel_element *elem,
+                              grpc_channel_element_args *args) {
+  channel_data *channeld = elem->channel_data;
+  grpc_compression_algorithm algo_idx;
+
+  grpc_compression_options_init(&channeld->compression_options);
+  channeld->compression_options.enabled_algorithms_bitset =
+      (uint32_t)grpc_channel_args_compression_algorithm_get_states(
+          args->channel_args);
+
+  channeld->default_compression_algorithm =
+      grpc_channel_args_get_compression_algorithm(args->channel_args);
+  /* Make sure the default isn't disabled. */
+  GPR_ASSERT(grpc_compression_options_is_algorithm_enabled(
+      &channeld->compression_options, channeld->default_compression_algorithm));
+  channeld->compression_options.default_compression_algorithm =
+      channeld->default_compression_algorithm;
+
+  channeld->supported_compression_algorithms = 0;
+  for (algo_idx = 0; algo_idx < GRPC_COMPRESS_ALGORITHMS_COUNT; ++algo_idx) {
+    /* skip disabled algorithms */
+    if (grpc_compression_options_is_algorithm_enabled(
+            &channeld->compression_options, algo_idx) == 0) {
+      continue;
+    }
+    channeld->supported_compression_algorithms |= 1u << algo_idx;
+  }
+
+  GPR_ASSERT(!args->is_last);
+}
+
+/* Destructor for channel data */
+static void destroy_channel_elem(grpc_exec_ctx *exec_ctx,
+                                 grpc_channel_element *elem) {}
+
+const grpc_channel_filter grpc_compress_filter = {
+    compress_start_transport_stream_op,
+    grpc_channel_next_op,
+    sizeof(call_data),
+    init_call_elem,
+    grpc_call_stack_ignore_set_pollset,
+    destroy_call_elem,
+    sizeof(channel_data),
+    init_channel_elem,
+    destroy_channel_elem,
+    grpc_call_next_get_peer,
+    "compress"};
diff --git a/src/core/lib/channel/compress_filter.h b/src/core/lib/channel/compress_filter.h
new file mode 100644
index 0000000000..8c208ac799
--- /dev/null
+++ b/src/core/lib/channel/compress_filter.h
@@ -0,0 +1,65 @@
+/*
+ *
+ * Copyright 2015-2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_CHANNEL_COMPRESS_FILTER_H
+#define GRPC_CORE_CHANNEL_COMPRESS_FILTER_H
+
+#include "src/core/channel/channel_stack.h"
+
+#define GRPC_COMPRESS_REQUEST_ALGORITHM_KEY "grpc-internal-encoding-request"
+
+/** Compression filter for outgoing data.
+ *
+ * See <grpc/compression.h> for the available compression settings.
+ *
+ * Compression settings may come from:
+ *  - Channel configuration, as established at channel creation time.
+ *  - The metadata accompanying the outgoing data to be compressed. This is
+ *    taken as a request only. We may choose not to honor it. The metadata key
+ *    is given by \a GRPC_COMPRESS_REQUEST_ALGORITHM_KEY.
+ *
+ * Compression can be disabled for concrete messages (for instance in order to
+ * prevent CRIME/BEAST type attacks) by having the GRPC_WRITE_NO_COMPRESS set in
+ * the BEGIN_MESSAGE flags.
+ *
+ * The attempted compression mechanism is added to the resulting initial
+ * metadata under the'grpc-encoding' key.
+ *
+ * If compression is actually performed, BEGIN_MESSAGE's flag is modified to
+ * incorporate GRPC_WRITE_INTERNAL_COMPRESS. Otherwise, and regardless of the
+ * aforementioned 'grpc-encoding' metadata value, data will pass through
+ * uncompressed. */
+
+extern const grpc_channel_filter grpc_compress_filter;
+
+#endif /* GRPC_CORE_CHANNEL_COMPRESS_FILTER_H */
diff --git a/src/core/lib/channel/connected_channel.c b/src/core/lib/channel/connected_channel.c
new file mode 100644
index 0000000000..df11d54297
--- /dev/null
+++ b/src/core/lib/channel/connected_channel.c
@@ -0,0 +1,176 @@
+/*
+ *
+ * Copyright 2015-2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/channel/connected_channel.h"
+
+#include <stdarg.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <grpc/byte_buffer.h>
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+#include <grpc/support/slice_buffer.h>
+#include "src/core/profiling/timers.h"
+#include "src/core/support/string.h"
+#include "src/core/transport/transport.h"
+
+#define MAX_BUFFER_LENGTH 8192
+
+typedef struct connected_channel_channel_data {
+  grpc_transport *transport;
+} channel_data;
+
+typedef struct connected_channel_call_data { void *unused; } call_data;
+
+/* We perform a small hack to locate transport data alongside the connected
+   channel data in call allocations, to allow everything to be pulled in minimal
+   cache line requests */
+#define TRANSPORT_STREAM_FROM_CALL_DATA(calld) ((grpc_stream *)((calld) + 1))
+#define CALL_DATA_FROM_TRANSPORT_STREAM(transport_stream) \
+  (((call_data *)(transport_stream)) - 1)
+
+/* Intercept a call operation and either push it directly up or translate it
+   into transport stream operations */
+static void con_start_transport_stream_op(grpc_exec_ctx *exec_ctx,
+                                          grpc_call_element *elem,
+                                          grpc_transport_stream_op *op) {
+  call_data *calld = elem->call_data;
+  channel_data *chand = elem->channel_data;
+  GRPC_CALL_LOG_OP(GPR_INFO, elem, op);
+
+  grpc_transport_perform_stream_op(exec_ctx, chand->transport,
+                                   TRANSPORT_STREAM_FROM_CALL_DATA(calld), op);
+}
+
+static void con_start_transport_op(grpc_exec_ctx *exec_ctx,
+                                   grpc_channel_element *elem,
+                                   grpc_transport_op *op) {
+  channel_data *chand = elem->channel_data;
+  grpc_transport_perform_op(exec_ctx, chand->transport, op);
+}
+
+/* Constructor for call_data */
+static void init_call_elem(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
+                           grpc_call_element_args *args) {
+  call_data *calld = elem->call_data;
+  channel_data *chand = elem->channel_data;
+  int r;
+
+  r = grpc_transport_init_stream(
+      exec_ctx, chand->transport, TRANSPORT_STREAM_FROM_CALL_DATA(calld),
+      &args->call_stack->refcount, args->server_transport_data);
+  GPR_ASSERT(r == 0);
+}
+
+static void set_pollset(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
+                        grpc_pollset *pollset) {
+  call_data *calld = elem->call_data;
+  channel_data *chand = elem->channel_data;
+  grpc_transport_set_pollset(exec_ctx, chand->transport,
+                             TRANSPORT_STREAM_FROM_CALL_DATA(calld), pollset);
+}
+
+/* Destructor for call_data */
+static void destroy_call_elem(grpc_exec_ctx *exec_ctx,
+                              grpc_call_element *elem) {
+  call_data *calld = elem->call_data;
+  channel_data *chand = elem->channel_data;
+  grpc_transport_destroy_stream(exec_ctx, chand->transport,
+                                TRANSPORT_STREAM_FROM_CALL_DATA(calld));
+}
+
+/* Constructor for channel_data */
+static void init_channel_elem(grpc_exec_ctx *exec_ctx,
+                              grpc_channel_element *elem,
+                              grpc_channel_element_args *args) {
+  channel_data *cd = (channel_data *)elem->channel_data;
+  GPR_ASSERT(args->is_last);
+  cd->transport = NULL;
+}
+
+/* Destructor for channel_data */
+static void destroy_channel_elem(grpc_exec_ctx *exec_ctx,
+                                 grpc_channel_element *elem) {
+  channel_data *cd = (channel_data *)elem->channel_data;
+  grpc_transport_destroy(exec_ctx, cd->transport);
+}
+
+static char *con_get_peer(grpc_exec_ctx *exec_ctx, grpc_call_element *elem) {
+  channel_data *chand = elem->channel_data;
+  return grpc_transport_get_peer(exec_ctx, chand->transport);
+}
+
+static const grpc_channel_filter connected_channel_filter = {
+    con_start_transport_stream_op,
+    con_start_transport_op,
+    sizeof(call_data),
+    init_call_elem,
+    set_pollset,
+    destroy_call_elem,
+    sizeof(channel_data),
+    init_channel_elem,
+    destroy_channel_elem,
+    con_get_peer,
+    "connected",
+};
+
+static void bind_transport(grpc_channel_stack *channel_stack,
+                           grpc_channel_element *elem, void *t) {
+  channel_data *cd = (channel_data *)elem->channel_data;
+  GPR_ASSERT(elem->filter == &connected_channel_filter);
+  GPR_ASSERT(cd->transport == NULL);
+  cd->transport = t;
+
+  /* HACK(ctiller): increase call stack size for the channel to make space
+     for channel data. We need a cleaner (but performant) way to do this,
+     and I'm not sure what that is yet.
+     This is only "safe" because call stacks place no additional data after
+     the last call element, and the last call element MUST be the connected
+     channel. */
+  channel_stack->call_stack_size += grpc_transport_stream_size(t);
+}
+
+bool grpc_add_connected_filter(grpc_channel_stack_builder *builder,
+                               void *arg_must_be_null) {
+  GPR_ASSERT(arg_must_be_null == NULL);
+  grpc_transport *t = grpc_channel_stack_builder_get_transport(builder);
+  GPR_ASSERT(t != NULL);
+  return grpc_channel_stack_builder_append_filter(
+      builder, &connected_channel_filter, bind_transport, t);
+}
+
+grpc_stream *grpc_connected_channel_get_stream(grpc_call_element *elem) {
+  call_data *calld = elem->call_data;
+  return TRANSPORT_STREAM_FROM_CALL_DATA(calld);
+}
diff --git a/src/core/lib/channel/connected_channel.h b/src/core/lib/channel/connected_channel.h
new file mode 100644
index 0000000000..7c0c8359a4
--- /dev/null
+++ b/src/core/lib/channel/connected_channel.h
@@ -0,0 +1,42 @@
+/*
+ *
+ * Copyright 2015-2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_CHANNEL_CONNECTED_CHANNEL_H
+#define GRPC_CORE_CHANNEL_CONNECTED_CHANNEL_H
+
+#include "src/core/channel/channel_stack_builder.h"
+
+bool grpc_add_connected_filter(grpc_channel_stack_builder *builder,
+                               void *arg_must_be_null);
+
+#endif /* GRPC_CORE_CHANNEL_CONNECTED_CHANNEL_H */
diff --git a/src/core/lib/channel/context.h b/src/core/lib/channel/context.h
new file mode 100644
index 0000000000..db217dc133
--- /dev/null
+++ b/src/core/lib/channel/context.h
@@ -0,0 +1,49 @@
+/*
+ *
+ * Copyright 2015-2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_CHANNEL_CONTEXT_H
+#define GRPC_CORE_CHANNEL_CONTEXT_H
+
+/* Call object context pointers */
+typedef enum {
+  GRPC_CONTEXT_SECURITY = 0,
+  GRPC_CONTEXT_TRACING,
+  GRPC_CONTEXT_COUNT
+} grpc_context_index;
+
+typedef struct {
+  void *value;
+  void (*destroy)(void *);
+} grpc_call_context_element;
+
+#endif /* GRPC_CORE_CHANNEL_CONTEXT_H */
diff --git a/src/core/lib/channel/http_client_filter.c b/src/core/lib/channel/http_client_filter.c
new file mode 100644
index 0000000000..582427daf9
--- /dev/null
+++ b/src/core/lib/channel/http_client_filter.c
@@ -0,0 +1,255 @@
+/*
+ * Copyright 2015-2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/channel/http_client_filter.h"
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+#include <grpc/support/string_util.h>
+#include <string.h>
+#include "src/core/profiling/timers.h"
+#include "src/core/support/string.h"
+#include "src/core/transport/static_metadata.h"
+
+typedef struct call_data {
+  grpc_linked_mdelem method;
+  grpc_linked_mdelem scheme;
+  grpc_linked_mdelem authority;
+  grpc_linked_mdelem te_trailers;
+  grpc_linked_mdelem content_type;
+  grpc_linked_mdelem user_agent;
+
+  grpc_metadata_batch *recv_initial_metadata;
+
+  /** Closure to call when finished with the hc_on_recv hook */
+  grpc_closure *on_done_recv;
+  /** Receive closures are chained: we inject this closure as the on_done_recv
+      up-call on transport_op, and remember to call our on_done_recv member
+      after handling it. */
+  grpc_closure hc_on_recv;
+} call_data;
+
+typedef struct channel_data {
+  grpc_mdelem *static_scheme;
+  grpc_mdelem *user_agent;
+} channel_data;
+
+typedef struct {
+  grpc_call_element *elem;
+  grpc_exec_ctx *exec_ctx;
+} client_recv_filter_args;
+
+static grpc_mdelem *client_recv_filter(void *user_data, grpc_mdelem *md) {
+  client_recv_filter_args *a = user_data;
+  if (md == GRPC_MDELEM_STATUS_200) {
+    return NULL;
+  } else if (md->key == GRPC_MDSTR_STATUS) {
+    grpc_call_element_send_cancel(a->exec_ctx, a->elem);
+    return NULL;
+  } else if (md->key == GRPC_MDSTR_CONTENT_TYPE) {
+    return NULL;
+  }
+  return md;
+}
+
+static void hc_on_recv(grpc_exec_ctx *exec_ctx, void *user_data, bool success) {
+  grpc_call_element *elem = user_data;
+  call_data *calld = elem->call_data;
+  client_recv_filter_args a;
+  a.elem = elem;
+  a.exec_ctx = exec_ctx;
+  grpc_metadata_batch_filter(calld->recv_initial_metadata, client_recv_filter,
+                             &a);
+  calld->on_done_recv->cb(exec_ctx, calld->on_done_recv->cb_arg, success);
+}
+
+static grpc_mdelem *client_strip_filter(void *user_data, grpc_mdelem *md) {
+  /* eat the things we'd like to set ourselves */
+  if (md->key == GRPC_MDSTR_METHOD) return NULL;
+  if (md->key == GRPC_MDSTR_SCHEME) return NULL;
+  if (md->key == GRPC_MDSTR_TE) return NULL;
+  if (md->key == GRPC_MDSTR_CONTENT_TYPE) return NULL;
+  if (md->key == GRPC_MDSTR_USER_AGENT) return NULL;
+  return md;
+}
+
+static void hc_mutate_op(grpc_call_element *elem,
+                         grpc_transport_stream_op *op) {
+  /* grab pointers to our data from the call element */
+  call_data *calld = elem->call_data;
+  channel_data *channeld = elem->channel_data;
+  if (op->send_initial_metadata != NULL) {
+    grpc_metadata_batch_filter(op->send_initial_metadata, client_strip_filter,
+                               elem);
+    /* Send : prefixed headers, which have to be before any application
+       layer headers. */
+    grpc_metadata_batch_add_head(op->send_initial_metadata, &calld->method,
+                                 GRPC_MDELEM_METHOD_POST);
+    grpc_metadata_batch_add_head(op->send_initial_metadata, &calld->scheme,
+                                 channeld->static_scheme);
+    grpc_metadata_batch_add_tail(op->send_initial_metadata, &calld->te_trailers,
+                                 GRPC_MDELEM_TE_TRAILERS);
+    grpc_metadata_batch_add_tail(
+        op->send_initial_metadata, &calld->content_type,
+        GRPC_MDELEM_CONTENT_TYPE_APPLICATION_SLASH_GRPC);
+    grpc_metadata_batch_add_tail(op->send_initial_metadata, &calld->user_agent,
+                                 GRPC_MDELEM_REF(channeld->user_agent));
+  }
+
+  if (op->recv_initial_metadata != NULL) {
+    /* substitute our callback for the higher callback */
+    calld->recv_initial_metadata = op->recv_initial_metadata;
+    calld->on_done_recv = op->recv_initial_metadata_ready;
+    op->recv_initial_metadata_ready = &calld->hc_on_recv;
+  }
+}
+
+static void hc_start_transport_op(grpc_exec_ctx *exec_ctx,
+                                  grpc_call_element *elem,
+                                  grpc_transport_stream_op *op) {
+  GPR_TIMER_BEGIN("hc_start_transport_op", 0);
+  GRPC_CALL_LOG_OP(GPR_INFO, elem, op);
+  hc_mutate_op(elem, op);
+  GPR_TIMER_END("hc_start_transport_op", 0);
+  grpc_call_next_op(exec_ctx, elem, op);
+}
+
+/* Constructor for call_data */
+static void init_call_elem(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
+                           grpc_call_element_args *args) {
+  call_data *calld = elem->call_data;
+  calld->on_done_recv = NULL;
+  grpc_closure_init(&calld->hc_on_recv, hc_on_recv, elem);
+}
+
+/* Destructor for call_data */
+static void destroy_call_elem(grpc_exec_ctx *exec_ctx,
+                              grpc_call_element *elem) {}
+
+static grpc_mdelem *scheme_from_args(const grpc_channel_args *args) {
+  unsigned i;
+  size_t j;
+  grpc_mdelem *valid_schemes[] = {GRPC_MDELEM_SCHEME_HTTP,
+                                  GRPC_MDELEM_SCHEME_HTTPS};
+  if (args != NULL) {
+    for (i = 0; i < args->num_args; ++i) {
+      if (args->args[i].type == GRPC_ARG_STRING &&
+          strcmp(args->args[i].key, GRPC_ARG_HTTP2_SCHEME) == 0) {
+        for (j = 0; j < GPR_ARRAY_SIZE(valid_schemes); j++) {
+          if (0 == strcmp(grpc_mdstr_as_c_string(valid_schemes[j]->value),
+                          args->args[i].value.string)) {
+            return valid_schemes[j];
+          }
+        }
+      }
+    }
+  }
+  return GRPC_MDELEM_SCHEME_HTTP;
+}
+
+static grpc_mdstr *user_agent_from_args(const grpc_channel_args *args) {
+  gpr_strvec v;
+  size_t i;
+  int is_first = 1;
+  char *tmp;
+  grpc_mdstr *result;
+
+  gpr_strvec_init(&v);
+
+  for (i = 0; args && i < args->num_args; i++) {
+    if (0 == strcmp(args->args[i].key, GRPC_ARG_PRIMARY_USER_AGENT_STRING)) {
+      if (args->args[i].type != GRPC_ARG_STRING) {
+        gpr_log(GPR_ERROR, "Channel argument '%s' should be a string",
+                GRPC_ARG_PRIMARY_USER_AGENT_STRING);
+      } else {
+        if (!is_first) gpr_strvec_add(&v, gpr_strdup(" "));
+        is_first = 0;
+        gpr_strvec_add(&v, gpr_strdup(args->args[i].value.string));
+      }
+    }
+  }
+
+  gpr_asprintf(&tmp, "%sgrpc-c/%s (%s)", is_first ? "" : " ",
+               grpc_version_string(), GPR_PLATFORM_STRING);
+  is_first = 0;
+  gpr_strvec_add(&v, tmp);
+
+  for (i = 0; args && i < args->num_args; i++) {
+    if (0 == strcmp(args->args[i].key, GRPC_ARG_SECONDARY_USER_AGENT_STRING)) {
+      if (args->args[i].type != GRPC_ARG_STRING) {
+        gpr_log(GPR_ERROR, "Channel argument '%s' should be a string",
+                GRPC_ARG_SECONDARY_USER_AGENT_STRING);
+      } else {
+        if (!is_first) gpr_strvec_add(&v, gpr_strdup(" "));
+        is_first = 0;
+        gpr_strvec_add(&v, gpr_strdup(args->args[i].value.string));
+      }
+    }
+  }
+
+  tmp = gpr_strvec_flatten(&v, NULL);
+  gpr_strvec_destroy(&v);
+  result = grpc_mdstr_from_string(tmp);
+  gpr_free(tmp);
+
+  return result;
+}
+
+/* Constructor for channel_data */
+static void init_channel_elem(grpc_exec_ctx *exec_ctx,
+                              grpc_channel_element *elem,
+                              grpc_channel_element_args *args) {
+  channel_data *chand = elem->channel_data;
+  GPR_ASSERT(!args->is_last);
+  chand->static_scheme = scheme_from_args(args->channel_args);
+  chand->user_agent = grpc_mdelem_from_metadata_strings(
+      GRPC_MDSTR_USER_AGENT, user_agent_from_args(args->channel_args));
+}
+
+/* Destructor for channel data */
+static void destroy_channel_elem(grpc_exec_ctx *exec_ctx,
+                                 grpc_channel_element *elem) {
+  channel_data *chand = elem->channel_data;
+  GRPC_MDELEM_UNREF(chand->user_agent);
+}
+
+const grpc_channel_filter grpc_http_client_filter = {
+    hc_start_transport_op,
+    grpc_channel_next_op,
+    sizeof(call_data),
+    init_call_elem,
+    grpc_call_stack_ignore_set_pollset,
+    destroy_call_elem,
+    sizeof(channel_data),
+    init_channel_elem,
+    destroy_channel_elem,
+    grpc_call_next_get_peer,
+    "http-client"};
diff --git a/src/core/lib/channel/http_client_filter.h b/src/core/lib/channel/http_client_filter.h
new file mode 100644
index 0000000000..6f619bbf00
--- /dev/null
+++ b/src/core/lib/channel/http_client_filter.h
@@ -0,0 +1,44 @@
+/*
+ *
+ * Copyright 2015-2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_CHANNEL_HTTP_CLIENT_FILTER_H
+#define GRPC_CORE_CHANNEL_HTTP_CLIENT_FILTER_H
+
+#include "src/core/channel/channel_stack.h"
+
+/* Processes metadata on the client side for HTTP2 transports */
+extern const grpc_channel_filter grpc_http_client_filter;
+
+#define GRPC_ARG_HTTP2_SCHEME "grpc.http2_scheme"
+
+#endif /* GRPC_CORE_CHANNEL_HTTP_CLIENT_FILTER_H */
diff --git a/src/core/lib/channel/http_server_filter.c b/src/core/lib/channel/http_server_filter.c
new file mode 100644
index 0000000000..1a2e0c5db3
--- /dev/null
+++ b/src/core/lib/channel/http_server_filter.c
@@ -0,0 +1,240 @@
+/*
+ *
+ * Copyright 2015-2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/channel/http_server_filter.h"
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+#include <string.h>
+#include "src/core/profiling/timers.h"
+#include "src/core/transport/static_metadata.h"
+
+typedef struct call_data {
+  uint8_t seen_path;
+  uint8_t seen_post;
+  uint8_t sent_status;
+  uint8_t seen_scheme;
+  uint8_t seen_te_trailers;
+  uint8_t seen_authority;
+  grpc_linked_mdelem status;
+  grpc_linked_mdelem content_type;
+
+  grpc_metadata_batch *recv_initial_metadata;
+  /** Closure to call when finished with the hs_on_recv hook */
+  grpc_closure *on_done_recv;
+  /** Receive closures are chained: we inject this closure as the on_done_recv
+      up-call on transport_op, and remember to call our on_done_recv member
+      after handling it. */
+  grpc_closure hs_on_recv;
+} call_data;
+
+typedef struct channel_data { uint8_t unused; } channel_data;
+
+typedef struct {
+  grpc_call_element *elem;
+  grpc_exec_ctx *exec_ctx;
+} server_filter_args;
+
+static grpc_mdelem *server_filter(void *user_data, grpc_mdelem *md) {
+  server_filter_args *a = user_data;
+  grpc_call_element *elem = a->elem;
+  call_data *calld = elem->call_data;
+
+  /* Check if it is one of the headers we care about. */
+  if (md == GRPC_MDELEM_TE_TRAILERS || md == GRPC_MDELEM_METHOD_POST ||
+      md == GRPC_MDELEM_SCHEME_HTTP || md == GRPC_MDELEM_SCHEME_HTTPS ||
+      md == GRPC_MDELEM_CONTENT_TYPE_APPLICATION_SLASH_GRPC) {
+    /* swallow it */
+    if (md == GRPC_MDELEM_METHOD_POST) {
+      calld->seen_post = 1;
+    } else if (md->key == GRPC_MDSTR_SCHEME) {
+      calld->seen_scheme = 1;
+    } else if (md == GRPC_MDELEM_TE_TRAILERS) {
+      calld->seen_te_trailers = 1;
+    }
+    /* TODO(klempner): Track that we've seen all the headers we should
+       require */
+    return NULL;
+  } else if (md->key == GRPC_MDSTR_CONTENT_TYPE) {
+    if (strncmp(grpc_mdstr_as_c_string(md->value), "application/grpc+", 17) ==
+        0) {
+      /* Although the C implementation doesn't (currently) generate them,
+         any custom +-suffix is explicitly valid. */
+      /* TODO(klempner): We should consider preallocating common values such
+         as +proto or +json, or at least stashing them if we see them. */
+      /* TODO(klempner): Should we be surfacing this to application code? */
+    } else {
+      /* TODO(klempner): We're currently allowing this, but we shouldn't
+         see it without a proxy so log for now. */
+      gpr_log(GPR_INFO, "Unexpected content-type %s",
+              grpc_mdstr_as_c_string(md->value));
+    }
+    return NULL;
+  } else if (md->key == GRPC_MDSTR_TE || md->key == GRPC_MDSTR_METHOD ||
+             md->key == GRPC_MDSTR_SCHEME) {
+    gpr_log(GPR_ERROR, "Invalid %s: header: '%s'",
+            grpc_mdstr_as_c_string(md->key), grpc_mdstr_as_c_string(md->value));
+    /* swallow it and error everything out. */
+    /* TODO(klempner): We ought to generate more descriptive error messages
+       on the wire here. */
+    grpc_call_element_send_cancel(a->exec_ctx, elem);
+    return NULL;
+  } else if (md->key == GRPC_MDSTR_PATH) {
+    if (calld->seen_path) {
+      gpr_log(GPR_ERROR, "Received :path twice");
+      return NULL;
+    }
+    calld->seen_path = 1;
+    return md;
+  } else if (md->key == GRPC_MDSTR_AUTHORITY) {
+    calld->seen_authority = 1;
+    return md;
+  } else if (md->key == GRPC_MDSTR_HOST) {
+    /* translate host to :authority since :authority may be
+       omitted */
+    grpc_mdelem *authority = grpc_mdelem_from_metadata_strings(
+        GRPC_MDSTR_AUTHORITY, GRPC_MDSTR_REF(md->value));
+    calld->seen_authority = 1;
+    return authority;
+  } else {
+    return md;
+  }
+}
+
+static void hs_on_recv(grpc_exec_ctx *exec_ctx, void *user_data, bool success) {
+  grpc_call_element *elem = user_data;
+  call_data *calld = elem->call_data;
+  if (success) {
+    server_filter_args a;
+    a.elem = elem;
+    a.exec_ctx = exec_ctx;
+    grpc_metadata_batch_filter(calld->recv_initial_metadata, server_filter, &a);
+    /* Have we seen the required http2 transport headers?
+       (:method, :scheme, content-type, with :path and :authority covered
+       at the channel level right now) */
+    if (calld->seen_post && calld->seen_scheme && calld->seen_te_trailers &&
+        calld->seen_path && calld->seen_authority) {
+      /* do nothing */
+    } else {
+      if (!calld->seen_path) {
+        gpr_log(GPR_ERROR, "Missing :path header");
+      }
+      if (!calld->seen_authority) {
+        gpr_log(GPR_ERROR, "Missing :authority header");
+      }
+      if (!calld->seen_post) {
+        gpr_log(GPR_ERROR, "Missing :method header");
+      }
+      if (!calld->seen_scheme) {
+        gpr_log(GPR_ERROR, "Missing :scheme header");
+      }
+      if (!calld->seen_te_trailers) {
+        gpr_log(GPR_ERROR, "Missing te trailers header");
+      }
+      /* Error this call out */
+      success = 0;
+      grpc_call_element_send_cancel(exec_ctx, elem);
+    }
+  }
+  calld->on_done_recv->cb(exec_ctx, calld->on_done_recv->cb_arg, success);
+}
+
+static void hs_mutate_op(grpc_call_element *elem,
+                         grpc_transport_stream_op *op) {
+  /* grab pointers to our data from the call element */
+  call_data *calld = elem->call_data;
+
+  if (op->send_initial_metadata != NULL && !calld->sent_status) {
+    calld->sent_status = 1;
+    grpc_metadata_batch_add_head(op->send_initial_metadata, &calld->status,
+                                 GRPC_MDELEM_STATUS_200);
+    grpc_metadata_batch_add_tail(
+        op->send_initial_metadata, &calld->content_type,
+        GRPC_MDELEM_CONTENT_TYPE_APPLICATION_SLASH_GRPC);
+  }
+
+  if (op->recv_initial_metadata) {
+    /* substitute our callback for the higher callback */
+    calld->recv_initial_metadata = op->recv_initial_metadata;
+    calld->on_done_recv = op->recv_initial_metadata_ready;
+    op->recv_initial_metadata_ready = &calld->hs_on_recv;
+  }
+}
+
+static void hs_start_transport_op(grpc_exec_ctx *exec_ctx,
+                                  grpc_call_element *elem,
+                                  grpc_transport_stream_op *op) {
+  GRPC_CALL_LOG_OP(GPR_INFO, elem, op);
+  GPR_TIMER_BEGIN("hs_start_transport_op", 0);
+  hs_mutate_op(elem, op);
+  grpc_call_next_op(exec_ctx, elem, op);
+  GPR_TIMER_END("hs_start_transport_op", 0);
+}
+
+/* Constructor for call_data */
+static void init_call_elem(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
+                           grpc_call_element_args *args) {
+  /* grab pointers to our data from the call element */
+  call_data *calld = elem->call_data;
+  /* initialize members */
+  memset(calld, 0, sizeof(*calld));
+  grpc_closure_init(&calld->hs_on_recv, hs_on_recv, elem);
+}
+
+/* Destructor for call_data */
+static void destroy_call_elem(grpc_exec_ctx *exec_ctx,
+                              grpc_call_element *elem) {}
+
+/* Constructor for channel_data */
+static void init_channel_elem(grpc_exec_ctx *exec_ctx,
+                              grpc_channel_element *elem,
+                              grpc_channel_element_args *args) {
+  GPR_ASSERT(!args->is_last);
+}
+
+/* Destructor for channel data */
+static void destroy_channel_elem(grpc_exec_ctx *exec_ctx,
+                                 grpc_channel_element *elem) {}
+
+const grpc_channel_filter grpc_http_server_filter = {
+    hs_start_transport_op,
+    grpc_channel_next_op,
+    sizeof(call_data),
+    init_call_elem,
+    grpc_call_stack_ignore_set_pollset,
+    destroy_call_elem,
+    sizeof(channel_data),
+    init_channel_elem,
+    destroy_channel_elem,
+    grpc_call_next_get_peer,
+    "http-server"};
diff --git a/src/core/lib/channel/http_server_filter.h b/src/core/lib/channel/http_server_filter.h
new file mode 100644
index 0000000000..528c8648fd
--- /dev/null
+++ b/src/core/lib/channel/http_server_filter.h
@@ -0,0 +1,42 @@
+/*
+ *
+ * Copyright 2015-2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_CHANNEL_HTTP_SERVER_FILTER_H
+#define GRPC_CORE_CHANNEL_HTTP_SERVER_FILTER_H
+
+#include "src/core/channel/channel_stack.h"
+
+/* Processes metadata on the client side for HTTP2 transports */
+extern const grpc_channel_filter grpc_http_server_filter;
+
+#endif /* GRPC_CORE_CHANNEL_HTTP_SERVER_FILTER_H */
diff --git a/src/core/lib/channel/subchannel_call_holder.c b/src/core/lib/channel/subchannel_call_holder.c
new file mode 100644
index 0000000000..9c087dc2a1
--- /dev/null
+++ b/src/core/lib/channel/subchannel_call_holder.c
@@ -0,0 +1,259 @@
+/*
+ *
+ * Copyright 2015-2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/channel/subchannel_call_holder.h"
+
+#include <grpc/support/alloc.h>
+
+#include "src/core/profiling/timers.h"
+
+#define GET_CALL(holder) \
+  ((grpc_subchannel_call *)(gpr_atm_acq_load(&(holder)->subchannel_call)))
+
+#define CANCELLED_CALL ((grpc_subchannel_call *)1)
+
+static void subchannel_ready(grpc_exec_ctx *exec_ctx, void *holder,
+                             bool success);
+static void retry_ops(grpc_exec_ctx *exec_ctx, void *retry_ops_args,
+                      bool success);
+
+static void add_waiting_locked(grpc_subchannel_call_holder *holder,
+                               grpc_transport_stream_op *op);
+static void fail_locked(grpc_exec_ctx *exec_ctx,
+                        grpc_subchannel_call_holder *holder);
+static void retry_waiting_locked(grpc_exec_ctx *exec_ctx,
+                                 grpc_subchannel_call_holder *holder);
+
+void grpc_subchannel_call_holder_init(
+    grpc_subchannel_call_holder *holder,
+    grpc_subchannel_call_holder_pick_subchannel pick_subchannel,
+    void *pick_subchannel_arg, grpc_call_stack *owning_call) {
+  gpr_atm_rel_store(&holder->subchannel_call, 0);
+  holder->pick_subchannel = pick_subchannel;
+  holder->pick_subchannel_arg = pick_subchannel_arg;
+  gpr_mu_init(&holder->mu);
+  holder->connected_subchannel = NULL;
+  holder->waiting_ops = NULL;
+  holder->waiting_ops_count = 0;
+  holder->waiting_ops_capacity = 0;
+  holder->creation_phase = GRPC_SUBCHANNEL_CALL_HOLDER_NOT_CREATING;
+  holder->owning_call = owning_call;
+}
+
+void grpc_subchannel_call_holder_destroy(grpc_exec_ctx *exec_ctx,
+                                         grpc_subchannel_call_holder *holder) {
+  grpc_subchannel_call *call = GET_CALL(holder);
+  if (call != NULL && call != CANCELLED_CALL) {
+    GRPC_SUBCHANNEL_CALL_UNREF(exec_ctx, call, "holder");
+  }
+  GPR_ASSERT(holder->creation_phase ==
+             GRPC_SUBCHANNEL_CALL_HOLDER_NOT_CREATING);
+  gpr_mu_destroy(&holder->mu);
+  GPR_ASSERT(holder->waiting_ops_count == 0);
+  gpr_free(holder->waiting_ops);
+}
+
+void grpc_subchannel_call_holder_perform_op(grpc_exec_ctx *exec_ctx,
+                                            grpc_subchannel_call_holder *holder,
+                                            grpc_transport_stream_op *op) {
+  /* try to (atomically) get the call */
+  grpc_subchannel_call *call = GET_CALL(holder);
+  GPR_TIMER_BEGIN("grpc_subchannel_call_holder_perform_op", 0);
+  if (call == CANCELLED_CALL) {
+    grpc_transport_stream_op_finish_with_failure(exec_ctx, op);
+    GPR_TIMER_END("grpc_subchannel_call_holder_perform_op", 0);
+    return;
+  }
+  if (call != NULL) {
+    grpc_subchannel_call_process_op(exec_ctx, call, op);
+    GPR_TIMER_END("grpc_subchannel_call_holder_perform_op", 0);
+    return;
+  }
+  /* we failed; lock and figure out what to do */
+  gpr_mu_lock(&holder->mu);
+retry:
+  /* need to recheck that another thread hasn't set the call */
+  call = GET_CALL(holder);
+  if (call == CANCELLED_CALL) {
+    gpr_mu_unlock(&holder->mu);
+    grpc_transport_stream_op_finish_with_failure(exec_ctx, op);
+    GPR_TIMER_END("grpc_subchannel_call_holder_perform_op", 0);
+    return;
+  }
+  if (call != NULL) {
+    gpr_mu_unlock(&holder->mu);
+    grpc_subchannel_call_process_op(exec_ctx, call, op);
+    GPR_TIMER_END("grpc_subchannel_call_holder_perform_op", 0);
+    return;
+  }
+  /* if this is a cancellation, then we can raise our cancelled flag */
+  if (op->cancel_with_status != GRPC_STATUS_OK) {
+    if (!gpr_atm_rel_cas(&holder->subchannel_call, 0, 1)) {
+      goto retry;
+    } else {
+      switch (holder->creation_phase) {
+        case GRPC_SUBCHANNEL_CALL_HOLDER_NOT_CREATING:
+          fail_locked(exec_ctx, holder);
+          break;
+        case GRPC_SUBCHANNEL_CALL_HOLDER_PICKING_SUBCHANNEL:
+          holder->pick_subchannel(exec_ctx, holder->pick_subchannel_arg, NULL,
+                                  &holder->connected_subchannel, NULL);
+          break;
+      }
+      gpr_mu_unlock(&holder->mu);
+      grpc_transport_stream_op_finish_with_failure(exec_ctx, op);
+      GPR_TIMER_END("grpc_subchannel_call_holder_perform_op", 0);
+      return;
+    }
+  }
+  /* if we don't have a subchannel, try to get one */
+  if (holder->creation_phase == GRPC_SUBCHANNEL_CALL_HOLDER_NOT_CREATING &&
+      holder->connected_subchannel == NULL &&
+      op->send_initial_metadata != NULL) {
+    holder->creation_phase = GRPC_SUBCHANNEL_CALL_HOLDER_PICKING_SUBCHANNEL;
+    grpc_closure_init(&holder->next_step, subchannel_ready, holder);
+    GRPC_CALL_STACK_REF(holder->owning_call, "pick_subchannel");
+    if (holder->pick_subchannel(
+            exec_ctx, holder->pick_subchannel_arg, op->send_initial_metadata,
+            &holder->connected_subchannel, &holder->next_step)) {
+      holder->creation_phase = GRPC_SUBCHANNEL_CALL_HOLDER_NOT_CREATING;
+      GRPC_CALL_STACK_UNREF(exec_ctx, holder->owning_call, "pick_subchannel");
+    }
+  }
+  /* if we've got a subchannel, then let's ask it to create a call */
+  if (holder->creation_phase == GRPC_SUBCHANNEL_CALL_HOLDER_NOT_CREATING &&
+      holder->connected_subchannel != NULL) {
+    gpr_atm_rel_store(
+        &holder->subchannel_call,
+        (gpr_atm)(uintptr_t)grpc_connected_subchannel_create_call(
+            exec_ctx, holder->connected_subchannel, holder->pollset));
+    retry_waiting_locked(exec_ctx, holder);
+    goto retry;
+  }
+  /* nothing to be done but wait */
+  add_waiting_locked(holder, op);
+  gpr_mu_unlock(&holder->mu);
+  GPR_TIMER_END("grpc_subchannel_call_holder_perform_op", 0);
+}
+
+static void subchannel_ready(grpc_exec_ctx *exec_ctx, void *arg, bool success) {
+  grpc_subchannel_call_holder *holder = arg;
+  gpr_mu_lock(&holder->mu);
+  GPR_ASSERT(holder->creation_phase ==
+             GRPC_SUBCHANNEL_CALL_HOLDER_PICKING_SUBCHANNEL);
+  holder->creation_phase = GRPC_SUBCHANNEL_CALL_HOLDER_NOT_CREATING;
+  if (holder->connected_subchannel == NULL) {
+    fail_locked(exec_ctx, holder);
+  } else if (1 == gpr_atm_acq_load(&holder->subchannel_call)) {
+    /* already cancelled before subchannel became ready */
+    fail_locked(exec_ctx, holder);
+  } else {
+    gpr_atm_rel_store(
+        &holder->subchannel_call,
+        (gpr_atm)(uintptr_t)grpc_connected_subchannel_create_call(
+            exec_ctx, holder->connected_subchannel, holder->pollset));
+    retry_waiting_locked(exec_ctx, holder);
+  }
+  gpr_mu_unlock(&holder->mu);
+  GRPC_CALL_STACK_UNREF(exec_ctx, holder->owning_call, "pick_subchannel");
+}
+
+typedef struct {
+  grpc_transport_stream_op *ops;
+  size_t nops;
+  grpc_subchannel_call *call;
+} retry_ops_args;
+
+static void retry_waiting_locked(grpc_exec_ctx *exec_ctx,
+                                 grpc_subchannel_call_holder *holder) {
+  retry_ops_args *a = gpr_malloc(sizeof(*a));
+  a->ops = holder->waiting_ops;
+  a->nops = holder->waiting_ops_count;
+  a->call = GET_CALL(holder);
+  if (a->call == CANCELLED_CALL) {
+    gpr_free(a);
+    fail_locked(exec_ctx, holder);
+    return;
+  }
+  holder->waiting_ops = NULL;
+  holder->waiting_ops_count = 0;
+  holder->waiting_ops_capacity = 0;
+  GRPC_SUBCHANNEL_CALL_REF(a->call, "retry_ops");
+  grpc_exec_ctx_enqueue(exec_ctx, grpc_closure_create(retry_ops, a), true,
+                        NULL);
+}
+
+static void retry_ops(grpc_exec_ctx *exec_ctx, void *args, bool success) {
+  retry_ops_args *a = args;
+  size_t i;
+  for (i = 0; i < a->nops; i++) {
+    grpc_subchannel_call_process_op(exec_ctx, a->call, &a->ops[i]);
+  }
+  GRPC_SUBCHANNEL_CALL_UNREF(exec_ctx, a->call, "retry_ops");
+  gpr_free(a->ops);
+  gpr_free(a);
+}
+
+static void add_waiting_locked(grpc_subchannel_call_holder *holder,
+                               grpc_transport_stream_op *op) {
+  GPR_TIMER_BEGIN("add_waiting_locked", 0);
+  if (holder->waiting_ops_count == holder->waiting_ops_capacity) {
+    holder->waiting_ops_capacity = GPR_MAX(3, 2 * holder->waiting_ops_capacity);
+    holder->waiting_ops =
+        gpr_realloc(holder->waiting_ops, holder->waiting_ops_capacity *
+                                             sizeof(*holder->waiting_ops));
+  }
+  holder->waiting_ops[holder->waiting_ops_count++] = *op;
+  GPR_TIMER_END("add_waiting_locked", 0);
+}
+
+static void fail_locked(grpc_exec_ctx *exec_ctx,
+                        grpc_subchannel_call_holder *holder) {
+  size_t i;
+  for (i = 0; i < holder->waiting_ops_count; i++) {
+    grpc_transport_stream_op_finish_with_failure(exec_ctx,
+                                                 &holder->waiting_ops[i]);
+  }
+  holder->waiting_ops_count = 0;
+}
+
+char *grpc_subchannel_call_holder_get_peer(
+    grpc_exec_ctx *exec_ctx, grpc_subchannel_call_holder *holder) {
+  grpc_subchannel_call *subchannel_call = GET_CALL(holder);
+
+  if (subchannel_call) {
+    return grpc_subchannel_call_get_peer(exec_ctx, subchannel_call);
+  } else {
+    return NULL;
+  }
+}
diff --git a/src/core/lib/channel/subchannel_call_holder.h b/src/core/lib/channel/subchannel_call_holder.h
new file mode 100644
index 0000000000..84b4657db4
--- /dev/null
+++ b/src/core/lib/channel/subchannel_call_holder.h
@@ -0,0 +1,97 @@
+/*
+ *
+ * Copyright 2015-2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_CHANNEL_SUBCHANNEL_CALL_HOLDER_H
+#define GRPC_CORE_CHANNEL_SUBCHANNEL_CALL_HOLDER_H
+
+#include "src/core/client_config/subchannel.h"
+
+/** Pick a subchannel for grpc_subchannel_call_holder;
+    Return 1 if subchannel is available immediately (in which case on_ready
+    should not be called), or 0 otherwise (in which case on_ready should be
+    called when the subchannel is available) */
+typedef int (*grpc_subchannel_call_holder_pick_subchannel)(
+    grpc_exec_ctx *exec_ctx, void *arg, grpc_metadata_batch *initial_metadata,
+    grpc_connected_subchannel **connected_subchannel, grpc_closure *on_ready);
+
+typedef enum {
+  GRPC_SUBCHANNEL_CALL_HOLDER_NOT_CREATING,
+  GRPC_SUBCHANNEL_CALL_HOLDER_PICKING_SUBCHANNEL
+} grpc_subchannel_call_holder_creation_phase;
+
+/** Wrapper for holding a pointer to grpc_subchannel_call, and the
+    associated machinery to create such a pointer.
+    Handles queueing of stream ops until a call object is ready, waiting
+    for initial metadata before trying to create a call object,
+    and handling cancellation gracefully.
+
+    The channel filter uses this as their call_data. */
+typedef struct grpc_subchannel_call_holder {
+  /** either 0 for no call, 1 for cancelled, or a pointer to a
+      grpc_subchannel_call */
+  gpr_atm subchannel_call;
+  /** Helper function to choose the subchannel on which to create
+      the call object. Channel filter delegates to the load
+      balancing policy (once it's ready). */
+  grpc_subchannel_call_holder_pick_subchannel pick_subchannel;
+  void *pick_subchannel_arg;
+
+  gpr_mu mu;
+
+  grpc_subchannel_call_holder_creation_phase creation_phase;
+  grpc_connected_subchannel *connected_subchannel;
+  grpc_pollset *pollset;
+
+  grpc_transport_stream_op *waiting_ops;
+  size_t waiting_ops_count;
+  size_t waiting_ops_capacity;
+
+  grpc_closure next_step;
+
+  grpc_call_stack *owning_call;
+} grpc_subchannel_call_holder;
+
+void grpc_subchannel_call_holder_init(
+    grpc_subchannel_call_holder *holder,
+    grpc_subchannel_call_holder_pick_subchannel pick_subchannel,
+    void *pick_subchannel_arg, grpc_call_stack *owning_call);
+void grpc_subchannel_call_holder_destroy(grpc_exec_ctx *exec_ctx,
+                                         grpc_subchannel_call_holder *holder);
+
+void grpc_subchannel_call_holder_perform_op(grpc_exec_ctx *exec_ctx,
+                                            grpc_subchannel_call_holder *holder,
+                                            grpc_transport_stream_op *op);
+char *grpc_subchannel_call_holder_get_peer(grpc_exec_ctx *exec_ctx,
+                                           grpc_subchannel_call_holder *holder);
+
+#endif /* GRPC_CORE_CHANNEL_SUBCHANNEL_CALL_HOLDER_H */