Merge pull request #5013 from a-veitch/tag_set_to_context

Change all instances of census_tag_set to census_context

7 files changed, 536 insertions, 650 deletions

diff --git a/src/core/census/context.c b/src/core/census/context.c
index cab58b653c..e60330de64 100644
--- a/src/core/census/context.c
+++ b/src/core/census/context.c
@@ -1,6 +1,6 @@
 /*
  *
- * Copyright 2015, Google Inc.
+ * Copyright 2015-2016, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -31,16 +31,500 @@
  *
  */
 
-#include "src/core/census/context.h"
-
-#include <string.h>
 #include <grpc/census.h>
 #include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+#include <grpc/support/port_platform.h>
+#include <grpc/support/useful.h>
+#include <stdbool.h>
+#include <string.h>
+#include "src/core/support/string.h"
+
+// Functions in this file support the public context API, including
+// encoding/decoding as part of context propagation across RPC's. The overall
+// requirements (in approximate priority order) for the
+// context representation:
+// 1. Efficient conversion to/from wire format
+// 2. Minimal bytes used on-wire
+// 3. Efficient context creation
+// 4. Efficient lookup of tag value for a key
+// 5. Efficient iteration over tags
+// 6. Minimal memory footprint
+//
+// Notes on tradeoffs/decisions:
+// * tag includes 1 byte length of key, as well as nil-terminating byte. These
+//   are to aid in efficient parsing and the ability to directly return key
+//   strings. This is more important than saving a single byte/tag on the wire.
+// * The wire encoding uses only single byte values. This eliminates the need
+//   to handle endian-ness conversions. It also means there is a hard upper
+//   limit of 255 for both CENSUS_MAX_TAG_KV_LEN and CENSUS_MAX_PROPAGATED_TAGS.
+// * Keep all tag information (keys/values/flags) in a single memory buffer,
+//   that can be directly copied to the wire.
+// * Binary tags share the same structure as, but are encoded separately from,
+//   non-binary tags. This is primarily because non-binary tags are far more
+//   likely to be repeated across multiple RPC calls, so are more efficiently
+//   cached and compressed in any metadata schemes.
+
+// Structure representing a set of tags. Essentially a count of number of tags
+// present, and pointer to a chunk of memory that contains the per-tag details.
+struct tag_set {
+  int ntags;        // number of tags.
+  int ntags_alloc;  // ntags + number of deleted tags (total number of tags
+  // in all of kvm). This will always be == ntags, except during the process
+  // of building a new tag set.
+  size_t kvm_size;  // number of bytes allocated for key/value storage.
+  size_t kvm_used;  // number of bytes of used key/value memory
+  char *kvm;        // key/value memory. Consists of repeated entries of:
+  //   Offset  Size  Description
+  //     0      1    Key length, including trailing 0. (K)
+  //     1      1    Value length. (V)
+  //     2      1    Flags
+  //     3      K    Key bytes
+  //     3 + K  V    Value bytes
+  //
+  // We refer to the first 3 entries as the 'tag header'. If extra values are
+  // introduced in the header, you will need to modify the TAG_HEADER_SIZE
+  // constant, the raw_tag structure (and everything that uses it) and the
+  // encode/decode functions appropriately.
+};
+
+// Number of bytes in tag header.
+#define TAG_HEADER_SIZE 3  // key length (1) + value length (1) + flags (1)
+// Offsets to tag header entries.
+#define KEY_LEN_OFFSET 0
+#define VALUE_LEN_OFFSET 1
+#define FLAG_OFFSET 2
+
+// raw_tag represents the raw-storage form of a tag in the kvm of a tag_set.
+struct raw_tag {
+  uint8_t key_len;
+  uint8_t value_len;
+  uint8_t flags;
+  char *key;
+  char *value;
+};
+
+// Use a reserved flag bit for indication of deleted tag.
+#define CENSUS_TAG_DELETED CENSUS_TAG_RESERVED
+#define CENSUS_TAG_IS_DELETED(flags) (flags & CENSUS_TAG_DELETED)
+
+// Primary (external) representation of a context. Composed of 3 underlying
+// tag_set structs, one for each of the binary/printable propagated tags, and
+// one for everything else. This is to efficiently support tag
+// encoding/decoding.
+struct census_context {
+  struct tag_set tags[3];
+  census_context_status status;
+};
+
+// Indices into the tags member of census_context
+#define PROPAGATED_TAGS 0
+#define PROPAGATED_BINARY_TAGS 1
+#define LOCAL_TAGS 2
+
+// Extract a raw tag given a pointer (raw) to the tag header. Allow for some
+// extra bytes in the tag header (see encode/decode functions for usage: this
+// allows for future expansion of the tag header).
+static char *decode_tag(struct raw_tag *tag, char *header, int offset) {
+  tag->key_len = (uint8_t)(*header++);
+  tag->value_len = (uint8_t)(*header++);
+  tag->flags = (uint8_t)(*header++);
+  header += offset;
+  tag->key = header;
+  header += tag->key_len;
+  tag->value = header;
+  return header + tag->value_len;
+}
 
-/* Placeholder implementation only. */
+// Make a copy (in 'to') of an existing tag_set.
+static void tag_set_copy(struct tag_set *to, const struct tag_set *from) {
+  memcpy(to, from, sizeof(struct tag_set));
+  to->kvm = gpr_malloc(to->kvm_size);
+  memcpy(to->kvm, from->kvm, from->kvm_used);
+}
+
+// Delete a tag from a tag_set, if it exists (returns true if it did).
+static bool tag_set_delete_tag(struct tag_set *tags, const char *key,
+                               size_t key_len) {
+  char *kvp = tags->kvm;
+  for (int i = 0; i < tags->ntags_alloc; i++) {
+    uint8_t *flags = (uint8_t *)(kvp + FLAG_OFFSET);
+    struct raw_tag tag;
+    kvp = decode_tag(&tag, kvp, 0);
+    if (CENSUS_TAG_IS_DELETED(tag.flags)) continue;
+    if ((key_len == tag.key_len) && (memcmp(key, tag.key, key_len) == 0)) {
+      *flags |= CENSUS_TAG_DELETED;
+      tags->ntags--;
+      return true;
+    }
+  }
+  return false;
+}
+
+// Delete a tag from a context, return true if it existed.
+static bool context_delete_tag(census_context *context, const census_tag *tag,
+                               size_t key_len) {
+  return (
+      tag_set_delete_tag(&context->tags[LOCAL_TAGS], tag->key, key_len) ||
+      tag_set_delete_tag(&context->tags[PROPAGATED_TAGS], tag->key, key_len) ||
+      tag_set_delete_tag(&context->tags[PROPAGATED_BINARY_TAGS], tag->key,
+                         key_len));
+}
+
+// Add a tag to a tag_set. Return true on success, false if the tag could
+// not be added because of constraints on tag set size. This function should
+// not be called if the tag may already exist (in a non-deleted state) in
+// the tag_set, as that would result in two tags with the same key.
+static bool tag_set_add_tag(struct tag_set *tags, const census_tag *tag,
+                            size_t key_len) {
+  if (tags->ntags == CENSUS_MAX_PROPAGATED_TAGS) {
+    return false;
+  }
+  const size_t tag_size = key_len + tag->value_len + TAG_HEADER_SIZE;
+  if (tags->kvm_used + tag_size > tags->kvm_size) {
+    // allocate new memory if needed
+    tags->kvm_size += 2 * CENSUS_MAX_TAG_KV_LEN + TAG_HEADER_SIZE;
+    char *new_kvm = gpr_malloc(tags->kvm_size);
+    memcpy(new_kvm, tags->kvm, tags->kvm_used);
+    gpr_free(tags->kvm);
+    tags->kvm = new_kvm;
+  }
+  char *kvp = tags->kvm + tags->kvm_used;
+  *kvp++ = (char)key_len;
+  *kvp++ = (char)tag->value_len;
+  // ensure reserved flags are not used.
+  *kvp++ = (char)(tag->flags & (CENSUS_TAG_PROPAGATE | CENSUS_TAG_STATS |
+                                CENSUS_TAG_BINARY));
+  memcpy(kvp, tag->key, key_len);
+  kvp += key_len;
+  memcpy(kvp, tag->value, tag->value_len);
+  tags->kvm_used += tag_size;
+  tags->ntags++;
+  tags->ntags_alloc++;
+  return true;
+}
+
+// Add/modify/delete a tag to/in a context. Caller must validate that tag key
+// etc. are valid.
+static void context_modify_tag(census_context *context, const census_tag *tag,
+                               size_t key_len) {
+  // First delete the tag if it is already present.
+  bool deleted = context_delete_tag(context, tag, key_len);
+  // Determine if we need to add it back.
+  bool call_add = tag->value != NULL && tag->value_len != 0;
+  bool added = false;
+  if (call_add) {
+    if (CENSUS_TAG_IS_PROPAGATED(tag->flags)) {
+      if (CENSUS_TAG_IS_BINARY(tag->flags)) {
+        added = tag_set_add_tag(&context->tags[PROPAGATED_BINARY_TAGS], tag,
+                                key_len);
+      } else {
+        added = tag_set_add_tag(&context->tags[PROPAGATED_TAGS], tag, key_len);
+      }
+    } else {
+      added = tag_set_add_tag(&context->tags[LOCAL_TAGS], tag, key_len);
+    }
+  }
+  if (deleted) {
+    if (call_add) {
+      context->status.n_modified_tags++;
+    } else {
+      context->status.n_deleted_tags++;
+    }
+  } else {
+    if (added) {
+      context->status.n_added_tags++;
+    } else {
+      context->status.n_ignored_tags++;
+    }
+  }
+}
+
+// Remove memory used for deleted tags from a tag set. Basic algorithm:
+// 1) Walk through tag set to find first deleted tag. Record where it is.
+// 2) Find the next not-deleted tag. Copy all of kvm from there to the end
+//    "over" the deleted tags
+// 3) repeat #1 and #2 until we have seen all tags
+// 4) if we are still looking for a not-deleted tag, then all the end portion
+//    of the kvm is deleted. Just reduce the used amount of memory by the
+//    appropriate amount.
+static void tag_set_flatten(struct tag_set *tags) {
+  if (tags->ntags == tags->ntags_alloc) return;
+  bool found_deleted = false;  // found a deleted tag.
+  char *kvp = tags->kvm;
+  char *dbase = NULL;  // record location of deleted tag
+  for (int i = 0; i < tags->ntags_alloc; i++) {
+    struct raw_tag tag;
+    char *next_kvp = decode_tag(&tag, kvp, 0);
+    if (found_deleted) {
+      if (!CENSUS_TAG_IS_DELETED(tag.flags)) {
+        ptrdiff_t reduce = kvp - dbase;  // #bytes in deleted tags
+        GPR_ASSERT(reduce > 0);
+        ptrdiff_t copy_size = tags->kvm + tags->kvm_used - kvp;
+        GPR_ASSERT(copy_size > 0);
+        memmove(dbase, kvp, (size_t)copy_size);
+        tags->kvm_used -= (size_t)reduce;
+        next_kvp -= reduce;
+        found_deleted = false;
+      }
+    } else {
+      if (CENSUS_TAG_IS_DELETED(tag.flags)) {
+        dbase = kvp;
+        found_deleted = true;
+      }
+    }
+    kvp = next_kvp;
+  }
+  if (found_deleted) {
+    GPR_ASSERT(dbase > tags->kvm);
+    tags->kvm_used = (size_t)(dbase - tags->kvm);
+  }
+  tags->ntags_alloc = tags->ntags;
+}
 
-size_t census_context_serialize(const census_context *context, char *buffer,
-                                size_t buf_size) {
-  /* TODO(aveitch): implement serialization */
+census_context *census_context_create(const census_context *base,
+                                      const census_tag *tags, int ntags,
+                                      census_context_status const **status) {
+  census_context *context = gpr_malloc(sizeof(census_context));
+  // If we are given a base, copy it into our new tag set. Otherwise set it
+  // to zero/NULL everything.
+  if (base == NULL) {
+    memset(context, 0, sizeof(census_context));
+  } else {
+    tag_set_copy(&context->tags[PROPAGATED_TAGS], &base->tags[PROPAGATED_TAGS]);
+    tag_set_copy(&context->tags[PROPAGATED_BINARY_TAGS],
+                 &base->tags[PROPAGATED_BINARY_TAGS]);
+    tag_set_copy(&context->tags[LOCAL_TAGS], &base->tags[LOCAL_TAGS]);
+    memset(&context->status, 0, sizeof(context->status));
+  }
+  // Walk over the additional tags and, for those that aren't invalid, modify
+  // the context to add/replace/delete as required.
+  for (int i = 0; i < ntags; i++) {
+    const census_tag *tag = &tags[i];
+    size_t key_len = strlen(tag->key) + 1;
+    // ignore the tag if it is too long/short.
+    if (key_len != 1 && key_len <= CENSUS_MAX_TAG_KV_LEN &&
+        tag->value_len <= CENSUS_MAX_TAG_KV_LEN) {
+      context_modify_tag(context, tag, key_len);
+    } else {
+      context->status.n_invalid_tags++;
+    }
+  }
+  // Remove any deleted tags, update status if needed, and return.
+  tag_set_flatten(&context->tags[PROPAGATED_TAGS]);
+  tag_set_flatten(&context->tags[PROPAGATED_BINARY_TAGS]);
+  tag_set_flatten(&context->tags[LOCAL_TAGS]);
+  context->status.n_propagated_tags = context->tags[PROPAGATED_TAGS].ntags;
+  context->status.n_propagated_binary_tags =
+      context->tags[PROPAGATED_BINARY_TAGS].ntags;
+  context->status.n_local_tags = context->tags[LOCAL_TAGS].ntags;
+  if (status) {
+    *status = &context->status;
+  }
+  return context;
+}
+
+const census_context_status *census_context_get_status(
+    const census_context *context) {
+  return &context->status;
+}
+
+void census_context_destroy(census_context *context) {
+  gpr_free(context->tags[PROPAGATED_TAGS].kvm);
+  gpr_free(context->tags[PROPAGATED_BINARY_TAGS].kvm);
+  gpr_free(context->tags[LOCAL_TAGS].kvm);
+  gpr_free(context);
+}
+
+void census_context_initialize_iterator(const census_context *context,
+                                        census_context_iterator *iterator) {
+  iterator->context = context;
+  iterator->index = 0;
+  if (context->tags[PROPAGATED_TAGS].ntags != 0) {
+    iterator->base = PROPAGATED_TAGS;
+    iterator->kvm = context->tags[PROPAGATED_TAGS].kvm;
+  } else if (context->tags[PROPAGATED_BINARY_TAGS].ntags != 0) {
+    iterator->base = PROPAGATED_BINARY_TAGS;
+    iterator->kvm = context->tags[PROPAGATED_BINARY_TAGS].kvm;
+  } else if (context->tags[LOCAL_TAGS].ntags != 0) {
+    iterator->base = LOCAL_TAGS;
+    iterator->kvm = context->tags[LOCAL_TAGS].kvm;
+  } else {
+    iterator->base = -1;
+  }
+}
+
+int census_context_next_tag(census_context_iterator *iterator,
+                            census_tag *tag) {
+  if (iterator->base < 0) {
+    return 0;
+  }
+  struct raw_tag raw;
+  iterator->kvm = decode_tag(&raw, iterator->kvm, 0);
+  tag->key = raw.key;
+  tag->value = raw.value;
+  tag->value_len = raw.value_len;
+  tag->flags = raw.flags;
+  if (++iterator->index == iterator->context->tags[iterator->base].ntags) {
+    do {
+      if (iterator->base == LOCAL_TAGS) {
+        iterator->base = -1;
+        return 1;
+      }
+    } while (iterator->context->tags[++iterator->base].ntags == 0);
+    iterator->index = 0;
+    iterator->kvm = iterator->context->tags[iterator->base].kvm;
+  }
+  return 1;
+}
+
+// Find a tag in a tag_set by key. Return true if found, false otherwise.
+static bool tag_set_get_tag(const struct tag_set *tags, const char *key,
+                            size_t key_len, census_tag *tag) {
+  char *kvp = tags->kvm;
+  for (int i = 0; i < tags->ntags; i++) {
+    struct raw_tag raw;
+    kvp = decode_tag(&raw, kvp, 0);
+    if (key_len == raw.key_len && memcmp(raw.key, key, key_len) == 0) {
+      tag->key = raw.key;
+      tag->value = raw.value;
+      tag->value_len = raw.value_len;
+      tag->flags = raw.flags;
+      return true;
+    }
+  }
+  return false;
+}
+
+int census_context_get_tag(const census_context *context, const char *key,
+                           census_tag *tag) {
+  size_t key_len = strlen(key) + 1;
+  if (key_len == 1) {
+    return 0;
+  }
+  if (tag_set_get_tag(&context->tags[PROPAGATED_TAGS], key, key_len, tag) ||
+      tag_set_get_tag(&context->tags[PROPAGATED_BINARY_TAGS], key, key_len,
+                      tag) ||
+      tag_set_get_tag(&context->tags[LOCAL_TAGS], key, key_len, tag)) {
+    return 1;
+  }
   return 0;
 }
+
+// Context encoding and decoding functions.
+//
+// Wire format for tag_set's on the wire:
+//
+// First, a tag set header:
+//
+// offset   bytes  description
+//   0        1    version number
+//   1        1    number of bytes in this header. This allows for future
+//                 expansion.
+//   2        1    number of bytes in each tag header.
+//   3        1    ntags value from tag set.
+//
+//   This is followed by the key/value memory from struct tag_set.
+
+#define ENCODED_VERSION 0      // Version number
+#define ENCODED_HEADER_SIZE 4  // size of tag set header
+
+// Encode a tag set. Returns 0 if buffer is too small.
+static size_t tag_set_encode(const struct tag_set *tags, char *buffer,
+                             size_t buf_size) {
+  if (buf_size < ENCODED_HEADER_SIZE + tags->kvm_used) {
+    return 0;
+  }
+  buf_size -= ENCODED_HEADER_SIZE;
+  *buffer++ = (char)ENCODED_VERSION;
+  *buffer++ = (char)ENCODED_HEADER_SIZE;
+  *buffer++ = (char)TAG_HEADER_SIZE;
+  *buffer++ = (char)tags->ntags;
+  if (tags->ntags == 0) {
+    return ENCODED_HEADER_SIZE;
+  }
+  memcpy(buffer, tags->kvm, tags->kvm_used);
+  return ENCODED_HEADER_SIZE + tags->kvm_used;
+}
+
+char *census_context_encode(const census_context *context, char *buffer,
+                            size_t buf_size, size_t *print_buf_size,
+                            size_t *bin_buf_size) {
+  *print_buf_size =
+      tag_set_encode(&context->tags[PROPAGATED_TAGS], buffer, buf_size);
+  if (*print_buf_size == 0) {
+    return NULL;
+  }
+  char *b_buffer = buffer + *print_buf_size;
+  *bin_buf_size = tag_set_encode(&context->tags[PROPAGATED_BINARY_TAGS],
+                                 b_buffer, buf_size - *print_buf_size);
+  if (*bin_buf_size == 0) {
+    return NULL;
+  }
+  return b_buffer;
+}
+
+// Decode a tag set.
+static void tag_set_decode(struct tag_set *tags, const char *buffer,
+                           size_t size) {
+  uint8_t version = (uint8_t)(*buffer++);
+  uint8_t header_size = (uint8_t)(*buffer++);
+  uint8_t tag_header_size = (uint8_t)(*buffer++);
+  tags->ntags = tags->ntags_alloc = (int)(*buffer++);
+  if (tags->ntags == 0) {
+    tags->ntags_alloc = 0;
+    tags->kvm_size = 0;
+    tags->kvm_used = 0;
+    tags->kvm = NULL;
+    return;
+  }
+  if (header_size != ENCODED_HEADER_SIZE) {
+    GPR_ASSERT(version != ENCODED_VERSION);
+    GPR_ASSERT(ENCODED_HEADER_SIZE < header_size);
+    buffer += (header_size - ENCODED_HEADER_SIZE);
+  }
+  tags->kvm_used = size - header_size;
+  tags->kvm_size = tags->kvm_used + CENSUS_MAX_TAG_KV_LEN;
+  tags->kvm = gpr_malloc(tags->kvm_size);
+  if (tag_header_size != TAG_HEADER_SIZE) {
+    // something new in the tag information. I don't understand it, so
+    // don't copy it over.
+    GPR_ASSERT(version != ENCODED_VERSION);
+    GPR_ASSERT(tag_header_size > TAG_HEADER_SIZE);
+    char *kvp = tags->kvm;
+    for (int i = 0; i < tags->ntags; i++) {
+      memcpy(kvp, buffer, TAG_HEADER_SIZE);
+      kvp += header_size;
+      struct raw_tag raw;
+      buffer =
+          decode_tag(&raw, (char *)buffer, tag_header_size - TAG_HEADER_SIZE);
+      memcpy(kvp, raw.key, (size_t)raw.key_len + raw.value_len);
+      kvp += raw.key_len + raw.value_len;
+    }
+  } else {
+    memcpy(tags->kvm, buffer, tags->kvm_used);
+  }
+}
+
+census_context *census_context_decode(const char *buffer, size_t size,
+                                      const char *bin_buffer, size_t bin_size) {
+  census_context *context = gpr_malloc(sizeof(census_context));
+  memset(&context->tags[LOCAL_TAGS], 0, sizeof(struct tag_set));
+  if (buffer == NULL) {
+    memset(&context->tags[PROPAGATED_TAGS], 0, sizeof(struct tag_set));
+  } else {
+    tag_set_decode(&context->tags[PROPAGATED_TAGS], buffer, size);
+  }
+  if (bin_buffer == NULL) {
+    memset(&context->tags[PROPAGATED_BINARY_TAGS], 0, sizeof(struct tag_set));
+  } else {
+    tag_set_decode(&context->tags[PROPAGATED_BINARY_TAGS], bin_buffer,
+                   bin_size);
+  }
+  memset(&context->status, 0, sizeof(context->status));
+  context->status.n_propagated_tags = context->tags[PROPAGATED_TAGS].ntags;
+  context->status.n_propagated_binary_tags =
+      context->tags[PROPAGATED_BINARY_TAGS].ntags;
+  // TODO(aveitch): check that BINARY flag is correct for each type.
+  return context;
+}
diff --git a/src/core/census/context.h b/src/core/census/context.h
deleted file mode 100644
index 700bcf86cf..0000000000
--- a/src/core/census/context.h
+++ /dev/null
@@ -1,47 +0,0 @@
-/*
- *
- * 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.
- *
- */
-
-#ifndef GRPC_INTERNAL_CORE_CENSUS_CONTEXT_H
-#define GRPC_INTERNAL_CORE_CENSUS_CONTEXT_H
-
-#include <grpc/census.h>
-
-#define GRPC_CENSUS_MAX_ON_THE_WIRE_TAG_BYTES 2048
-
-/* census_context is the in-memory representation of information needed to
- * maintain tracing, RPC statistics and resource usage information. */
-struct census_context {
-  census_tag_set *tags; /* Opaque data structure for census tags. */
-};
-
-#endif /* GRPC_INTERNAL_CORE_CENSUS_CONTEXT_H */
diff --git a/src/core/census/placeholders.c b/src/core/census/placeholders.c
index 5829cc9460..fe23d13971 100644
--- a/src/core/census/placeholders.c
+++ b/src/core/census/placeholders.c
@@ -37,11 +37,6 @@
 
 /* Placeholders for the pending APIs */
 
-census_tag_set *census_context_tag_set(census_context *context) {
-  (void)context;
-  abort();
-}
-
 int census_get_trace_record(census_trace_record *trace_record) {
   (void)trace_record;
   abort();
@@ -73,7 +68,7 @@ const census_aggregation *census_view_aggregrations(const census_view *view) {
   abort();
 }
 
-census_view *census_view_create(uint32_t metric_id, const census_tag_set *tags,
+census_view *census_view_create(uint32_t metric_id, const census_context *tags,
                                 const census_aggregation *aggregations,
                                 size_t naggregations) {
   (void)metric_id;
@@ -83,7 +78,7 @@ census_view *census_view_create(uint32_t metric_id, const census_tag_set *tags,
   abort();
 }
 
-const census_tag_set *census_view_tags(const census_view *view) {
+const census_context *census_view_tags(const census_view *view) {
   (void)view;
   abort();
 }
diff --git a/src/core/census/tag_set.c b/src/core/census/tag_set.c
deleted file mode 100644
index 9b65a1dfa1..0000000000
--- a/src/core/census/tag_set.c
+++ /dev/null
@@ -1,535 +0,0 @@
-/*
- *
- * 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 <grpc/census.h>
-#include <grpc/support/alloc.h>
-#include <grpc/support/log.h>
-#include <grpc/support/port_platform.h>
-#include <grpc/support/useful.h>
-#include <stdbool.h>
-#include <string.h>
-#include "src/core/support/string.h"
-
-// Functions in this file support the public tag_set API, as well as
-// encoding/decoding tag_sets as part of context propagation across
-// RPC's. The overall requirements (in approximate priority order) for the
-// tag_set representations:
-// 1. Efficient conversion to/from wire format
-// 2. Minimal bytes used on-wire
-// 3. Efficient tag set creation
-// 4. Efficient lookup of value for a key
-// 5. Efficient lookup of value for an index (to support iteration)
-// 6. Minimal memory footprint
-//
-// Notes on tradeoffs/decisions:
-// * tag includes 1 byte length of key, as well as nil-terminating byte. These
-//   are to aid in efficient parsing and the ability to directly return key
-//   strings. This is more important than saving a single byte/tag on the wire.
-// * The wire encoding uses only single byte values. This eliminates the need
-//   to handle endian-ness conversions. It also means there is a hard upper
-//   limit of 255 for both CENSUS_MAX_TAG_KV_LEN and CENSUS_MAX_PROPAGATED_TAGS.
-// * Keep all tag information (keys/values/flags) in a single memory buffer,
-//   that can be directly copied to the wire.14
-// * Binary tags share the same structure as, but are encoded separately from,
-//   non-binary tags. This is primarily because non-binary tags are far more
-//   likely to be repeated across multiple RPC calls, so are more efficiently
-//   cached and compressed in any metadata schemes.
-// * all lengths etc. are restricted to one byte. This eliminates endian
-//   issues.
-
-// Structure representing a set of tags. Essentially a count of number of tags
-// present, and pointer to a chunk of memory that contains the per-tag details.
-struct tag_set {
-  int ntags;        // number of tags.
-  int ntags_alloc;  // ntags + number of deleted tags (total number of tags
-  // in all of kvm). This will always be == ntags, except during the process
-  // of building a new tag set.
-  size_t kvm_size;  // number of bytes allocated for key/value storage.
-  size_t kvm_used;  // number of bytes of used key/value memory
-  char *kvm;        // key/value memory. Consists of repeated entries of:
-  //   Offset  Size  Description
-  //     0      1    Key length, including trailing 0. (K)
-  //     1      1    Value length. (V)
-  //     2      1    Flags
-  //     3      K    Key bytes
-  //     3 + K  V    Value bytes
-  //
-  // We refer to the first 3 entries as the 'tag header'. If extra values are
-  // introduced in the header, you will need to modify the TAG_HEADER_SIZE
-  // constant, the raw_tag structure (and everything that uses it) and the
-  // encode/decode functions appropriately.
-};
-
-// Number of bytes in tag header.
-#define TAG_HEADER_SIZE 3  // key length (1) + value length (1) + flags (1)
-// Offsets to tag header entries.
-#define KEY_LEN_OFFSET 0
-#define VALUE_LEN_OFFSET 1
-#define FLAG_OFFSET 2
-
-// raw_tag represents the raw-storage form of a tag in the kvm of a tag_set.
-struct raw_tag {
-  uint8_t key_len;
-  uint8_t value_len;
-  uint8_t flags;
-  char *key;
-  char *value;
-};
-
-// Use a reserved flag bit for indication of deleted tag.
-#define CENSUS_TAG_DELETED CENSUS_TAG_RESERVED
-#define CENSUS_TAG_IS_DELETED(flags) (flags & CENSUS_TAG_DELETED)
-
-// Primary (external) representation of a tag set. Composed of 3 underlying
-// tag_set structs, one for each of the binary/printable propagated tags, and
-// one for everything else. This is to efficiently support tag
-// encoding/decoding.
-struct census_tag_set {
-  struct tag_set tags[3];
-  census_tag_set_create_status status;
-};
-
-// Indices into the tags member of census_tag_set
-#define PROPAGATED_TAGS 0
-#define PROPAGATED_BINARY_TAGS 1
-#define LOCAL_TAGS 2
-
-// Extract a raw tag given a pointer (raw) to the tag header. Allow for some
-// extra bytes in the tag header (see encode/decode functions for usage: this
-// allows for future expansion of the tag header).
-static char *decode_tag(struct raw_tag *tag, char *header, int offset) {
-  tag->key_len = (uint8_t)(*header++);
-  tag->value_len = (uint8_t)(*header++);
-  tag->flags = (uint8_t)(*header++);
-  header += offset;
-  tag->key = header;
-  header += tag->key_len;
-  tag->value = header;
-  return header + tag->value_len;
-}
-
-// Make a copy (in 'to') of an existing tag_set.
-static void tag_set_copy(struct tag_set *to, const struct tag_set *from) {
-  memcpy(to, from, sizeof(struct tag_set));
-  to->kvm = gpr_malloc(to->kvm_size);
-  memcpy(to->kvm, from->kvm, from->kvm_used);
-}
-
-// Delete a tag from a tag_set, if it exists (returns true if it did).
-static bool tag_set_delete_tag(struct tag_set *tags, const char *key,
-                               size_t key_len) {
-  char *kvp = tags->kvm;
-  for (int i = 0; i < tags->ntags_alloc; i++) {
-    uint8_t *flags = (uint8_t *)(kvp + FLAG_OFFSET);
-    struct raw_tag tag;
-    kvp = decode_tag(&tag, kvp, 0);
-    if (CENSUS_TAG_IS_DELETED(tag.flags)) continue;
-    if ((key_len == tag.key_len) && (memcmp(key, tag.key, key_len) == 0)) {
-      *flags |= CENSUS_TAG_DELETED;
-      tags->ntags--;
-      return true;
-    }
-  }
-  return false;
-}
-
-// Delete a tag from a census_tag_set, return true if it existed.
-static bool cts_delete_tag(census_tag_set *tags, const census_tag *tag,
-                           size_t key_len) {
-  return (tag_set_delete_tag(&tags->tags[LOCAL_TAGS], tag->key, key_len) ||
-          tag_set_delete_tag(&tags->tags[PROPAGATED_TAGS], tag->key, key_len) ||
-          tag_set_delete_tag(&tags->tags[PROPAGATED_BINARY_TAGS], tag->key,
-                             key_len));
-}
-
-// Add a tag to a tag_set. Return true on sucess, false if the tag could
-// not be added because of constraints on tag set size. This function should
-// not be called if the tag may already exist (in a non-deleted state) in
-// the tag_set, as that would result in two tags with the same key.
-static bool tag_set_add_tag(struct tag_set *tags, const census_tag *tag,
-                            size_t key_len) {
-  if (tags->ntags == CENSUS_MAX_PROPAGATED_TAGS) {
-    return false;
-  }
-  const size_t tag_size = key_len + tag->value_len + TAG_HEADER_SIZE;
-  if (tags->kvm_used + tag_size > tags->kvm_size) {
-    // allocate new memory if needed
-    tags->kvm_size += 2 * CENSUS_MAX_TAG_KV_LEN + TAG_HEADER_SIZE;
-    char *new_kvm = gpr_malloc(tags->kvm_size);
-    memcpy(new_kvm, tags->kvm, tags->kvm_used);
-    gpr_free(tags->kvm);
-    tags->kvm = new_kvm;
-  }
-  char *kvp = tags->kvm + tags->kvm_used;
-  *kvp++ = (char)key_len;
-  *kvp++ = (char)tag->value_len;
-  // ensure reserved flags are not used.
-  *kvp++ = (char)(tag->flags & (CENSUS_TAG_PROPAGATE | CENSUS_TAG_STATS |
-                                CENSUS_TAG_BINARY));
-  memcpy(kvp, tag->key, key_len);
-  kvp += key_len;
-  memcpy(kvp, tag->value, tag->value_len);
-  tags->kvm_used += tag_size;
-  tags->ntags++;
-  tags->ntags_alloc++;
-  return true;
-}
-
-// Add/modify/delete a tag to/in a census_tag_set. Caller must validate that
-// tag key etc. are valid.
-static void cts_modify_tag(census_tag_set *tags, const census_tag *tag,
-                           size_t key_len) {
-  // First delete the tag if it is already present.
-  bool deleted = cts_delete_tag(tags, tag, key_len);
-  // Determine if we need to add it back.
-  bool call_add = tag->value != NULL && tag->value_len != 0;
-  bool added = false;
-  if (call_add) {
-    if (CENSUS_TAG_IS_PROPAGATED(tag->flags)) {
-      if (CENSUS_TAG_IS_BINARY(tag->flags)) {
-        added =
-            tag_set_add_tag(&tags->tags[PROPAGATED_BINARY_TAGS], tag, key_len);
-      } else {
-        added = tag_set_add_tag(&tags->tags[PROPAGATED_TAGS], tag, key_len);
-      }
-    } else {
-      added = tag_set_add_tag(&tags->tags[LOCAL_TAGS], tag, key_len);
-    }
-  }
-  if (deleted) {
-    if (call_add) {
-      tags->status.n_modified_tags++;
-    } else {
-      tags->status.n_deleted_tags++;
-    }
-  } else {
-    if (added) {
-      tags->status.n_added_tags++;
-    } else {
-      tags->status.n_ignored_tags++;
-    }
-  }
-}
-
-// Remove memory used for deleted tags from the tag set. Basic algorithm:
-// 1) Walk through tag set to find first deleted tag. Record where it is.
-// 2) Find the next not-deleted tag. Copy all of kvm from there to the end
-//    "over" the deleted tags
-// 3) repeat #1 and #2 until we have seen all tags
-// 4) if we are still looking for a not-deleted tag, then all the end portion
-//    of the kvm is deleted. Just reduce the used amount of memory by the
-//    appropriate amount.
-static void tag_set_flatten(struct tag_set *tags) {
-  if (tags->ntags == tags->ntags_alloc) return;
-  bool found_deleted = false;  // found a deleted tag.
-  char *kvp = tags->kvm;
-  char *dbase = NULL;  // record location of deleted tag
-  for (int i = 0; i < tags->ntags_alloc; i++) {
-    struct raw_tag tag;
-    char *next_kvp = decode_tag(&tag, kvp, 0);
-    if (found_deleted) {
-      if (!CENSUS_TAG_IS_DELETED(tag.flags)) {
-        ptrdiff_t reduce = kvp - dbase;  // #bytes in deleted tags
-        GPR_ASSERT(reduce > 0);
-        ptrdiff_t copy_size = tags->kvm + tags->kvm_used - kvp;
-        GPR_ASSERT(copy_size > 0);
-        memmove(dbase, kvp, (size_t)copy_size);
-        tags->kvm_used -= (size_t)reduce;
-        next_kvp -= reduce;
-        found_deleted = false;
-      }
-    } else {
-      if (CENSUS_TAG_IS_DELETED(tag.flags)) {
-        dbase = kvp;
-        found_deleted = true;
-      }
-    }
-    kvp = next_kvp;
-  }
-  if (found_deleted) {
-    GPR_ASSERT(dbase > tags->kvm);
-    tags->kvm_used = (size_t)(dbase - tags->kvm);
-  }
-  tags->ntags_alloc = tags->ntags;
-}
-
-census_tag_set *census_tag_set_create(
-    const census_tag_set *base, const census_tag *tags, int ntags,
-    census_tag_set_create_status const **status) {
-  census_tag_set *new_ts = gpr_malloc(sizeof(census_tag_set));
-  // If we are given a base, copy it into our new tag set. Otherwise set it
-  // to zero/NULL everything.
-  if (base == NULL) {
-    memset(new_ts, 0, sizeof(census_tag_set));
-  } else {
-    tag_set_copy(&new_ts->tags[PROPAGATED_TAGS], &base->tags[PROPAGATED_TAGS]);
-    tag_set_copy(&new_ts->tags[PROPAGATED_BINARY_TAGS],
-                 &base->tags[PROPAGATED_BINARY_TAGS]);
-    tag_set_copy(&new_ts->tags[LOCAL_TAGS], &base->tags[LOCAL_TAGS]);
-    memset(&new_ts->status, 0, sizeof(new_ts->status));
-  }
-  // Walk over the additional tags and, for those that aren't invalid, modify
-  // the tag set to add/replace/delete as required.
-  for (int i = 0; i < ntags; i++) {
-    const census_tag *tag = &tags[i];
-    size_t key_len = strlen(tag->key) + 1;
-    // ignore the tag if it is too long/short.
-    if (key_len != 1 && key_len <= CENSUS_MAX_TAG_KV_LEN &&
-        tag->value_len <= CENSUS_MAX_TAG_KV_LEN) {
-      cts_modify_tag(new_ts, tag, key_len);
-    } else {
-      new_ts->status.n_invalid_tags++;
-    }
-  }
-  // Remove any deleted tags, update status if needed, and return.
-  tag_set_flatten(&new_ts->tags[PROPAGATED_TAGS]);
-  tag_set_flatten(&new_ts->tags[PROPAGATED_BINARY_TAGS]);
-  tag_set_flatten(&new_ts->tags[LOCAL_TAGS]);
-  new_ts->status.n_propagated_tags = new_ts->tags[PROPAGATED_TAGS].ntags;
-  new_ts->status.n_propagated_binary_tags =
-      new_ts->tags[PROPAGATED_BINARY_TAGS].ntags;
-  new_ts->status.n_local_tags = new_ts->tags[LOCAL_TAGS].ntags;
-  if (status) {
-    *status = &new_ts->status;
-  }
-  return new_ts;
-}
-
-const census_tag_set_create_status *census_tag_set_get_create_status(
-    const census_tag_set *tags) {
-  return &tags->status;
-}
-
-void census_tag_set_destroy(census_tag_set *tags) {
-  gpr_free(tags->tags[PROPAGATED_TAGS].kvm);
-  gpr_free(tags->tags[PROPAGATED_BINARY_TAGS].kvm);
-  gpr_free(tags->tags[LOCAL_TAGS].kvm);
-  gpr_free(tags);
-}
-
-// Initialize a tag set iterator. Must be called before first use of the
-// iterator.
-void census_tag_set_initialize_iterator(const census_tag_set *tags,
-                                        census_tag_set_iterator *iterator) {
-  iterator->tags = tags;
-  iterator->index = 0;
-  if (tags->tags[PROPAGATED_TAGS].ntags != 0) {
-    iterator->base = PROPAGATED_TAGS;
-    iterator->kvm = tags->tags[PROPAGATED_TAGS].kvm;
-  } else if (tags->tags[PROPAGATED_BINARY_TAGS].ntags != 0) {
-    iterator->base = PROPAGATED_BINARY_TAGS;
-    iterator->kvm = tags->tags[PROPAGATED_BINARY_TAGS].kvm;
-  } else if (tags->tags[LOCAL_TAGS].ntags != 0) {
-    iterator->base = LOCAL_TAGS;
-    iterator->kvm = tags->tags[LOCAL_TAGS].kvm;
-  } else {
-    iterator->base = -1;
-  }
-}
-
-// Get the contents of the "next" tag in the tag set. If there are no more
-// tags in the tag set, returns 0 (and 'tag' contents will be unchanged),
-// otherwise returns 1. */
-int census_tag_set_next_tag(census_tag_set_iterator *iterator,
-                            census_tag *tag) {
-  if (iterator->base < 0) {
-    return 0;
-  }
-  struct raw_tag raw;
-  iterator->kvm = decode_tag(&raw, iterator->kvm, 0);
-  tag->key = raw.key;
-  tag->value = raw.value;
-  tag->value_len = raw.value_len;
-  tag->flags = raw.flags;
-  if (++iterator->index == iterator->tags->tags[iterator->base].ntags) {
-    do {
-      if (iterator->base == LOCAL_TAGS) {
-        iterator->base = -1;
-        return 1;
-      }
-    } while (iterator->tags->tags[++iterator->base].ntags == 0);
-    iterator->index = 0;
-    iterator->kvm = iterator->tags->tags[iterator->base].kvm;
-  }
-  return 1;
-}
-
-// Find a tag in a tag_set by key. Return true if found, false otherwise.
-static bool tag_set_get_tag_by_key(const struct tag_set *tags, const char *key,
-                                   size_t key_len, census_tag *tag) {
-  char *kvp = tags->kvm;
-  for (int i = 0; i < tags->ntags; i++) {
-    struct raw_tag raw;
-    kvp = decode_tag(&raw, kvp, 0);
-    if (key_len == raw.key_len && memcmp(raw.key, key, key_len) == 0) {
-      tag->key = raw.key;
-      tag->value = raw.value;
-      tag->value_len = raw.value_len;
-      tag->flags = raw.flags;
-      return true;
-    }
-  }
-  return false;
-}
-
-int census_tag_set_get_tag_by_key(const census_tag_set *tags, const char *key,
-                                  census_tag *tag) {
-  size_t key_len = strlen(key) + 1;
-  if (key_len == 1) {
-    return 0;
-  }
-  if (tag_set_get_tag_by_key(&tags->tags[PROPAGATED_TAGS], key, key_len, tag) ||
-      tag_set_get_tag_by_key(&tags->tags[PROPAGATED_BINARY_TAGS], key, key_len,
-                             tag) ||
-      tag_set_get_tag_by_key(&tags->tags[LOCAL_TAGS], key, key_len, tag)) {
-    return 1;
-  }
-  return 0;
-}
-
-// tag_set encoding and decoding functions.
-//
-// Wire format for tag sets on the wire:
-//
-// First, a tag set header:
-//
-// offset   bytes  description
-//   0        1    version number
-//   1        1    number of bytes in this header. This allows for future
-//                 expansion.
-//   2        1    number of bytes in each tag header.
-//   3        1    ntags value from tag set.
-//
-//   This is followed by the key/value memory from struct tag_set.
-
-#define ENCODED_VERSION 0      // Version number
-#define ENCODED_HEADER_SIZE 4  // size of tag set header
-
-// Encode a tag set. Returns 0 if buffer is too small.
-static size_t tag_set_encode(const struct tag_set *tags, char *buffer,
-                             size_t buf_size) {
-  if (buf_size < ENCODED_HEADER_SIZE + tags->kvm_used) {
-    return 0;
-  }
-  buf_size -= ENCODED_HEADER_SIZE;
-  *buffer++ = (char)ENCODED_VERSION;
-  *buffer++ = (char)ENCODED_HEADER_SIZE;
-  *buffer++ = (char)TAG_HEADER_SIZE;
-  *buffer++ = (char)tags->ntags;
-  if (tags->ntags == 0) {
-    return ENCODED_HEADER_SIZE;
-  }
-  memcpy(buffer, tags->kvm, tags->kvm_used);
-  return ENCODED_HEADER_SIZE + tags->kvm_used;
-}
-
-char *census_tag_set_encode(const census_tag_set *tags, char *buffer,
-                            size_t buf_size, size_t *print_buf_size,
-                            size_t *bin_buf_size) {
-  *print_buf_size =
-      tag_set_encode(&tags->tags[PROPAGATED_TAGS], buffer, buf_size);
-  if (*print_buf_size == 0) {
-    return NULL;
-  }
-  char *b_buffer = buffer + *print_buf_size;
-  *bin_buf_size = tag_set_encode(&tags->tags[PROPAGATED_BINARY_TAGS], b_buffer,
-                                 buf_size - *print_buf_size);
-  if (*bin_buf_size == 0) {
-    return NULL;
-  }
-  return b_buffer;
-}
-
-// Decode a tag set.
-static void tag_set_decode(struct tag_set *tags, const char *buffer,
-                           size_t size) {
-  uint8_t version = (uint8_t)(*buffer++);
-  uint8_t header_size = (uint8_t)(*buffer++);
-  uint8_t tag_header_size = (uint8_t)(*buffer++);
-  tags->ntags = tags->ntags_alloc = (int)(*buffer++);
-  if (tags->ntags == 0) {
-    tags->ntags_alloc = 0;
-    tags->kvm_size = 0;
-    tags->kvm_used = 0;
-    tags->kvm = NULL;
-    return;
-  }
-  if (header_size != ENCODED_HEADER_SIZE) {
-    GPR_ASSERT(version != ENCODED_VERSION);
-    GPR_ASSERT(ENCODED_HEADER_SIZE < header_size);
-    buffer += (header_size - ENCODED_HEADER_SIZE);
-  }
-  tags->kvm_used = size - header_size;
-  tags->kvm_size = tags->kvm_used + CENSUS_MAX_TAG_KV_LEN;
-  tags->kvm = gpr_malloc(tags->kvm_size);
-  if (tag_header_size != TAG_HEADER_SIZE) {
-    // something new in the tag information. I don't understand it, so
-    // don't copy it over.
-    GPR_ASSERT(version != ENCODED_VERSION);
-    GPR_ASSERT(tag_header_size > TAG_HEADER_SIZE);
-    char *kvp = tags->kvm;
-    for (int i = 0; i < tags->ntags; i++) {
-      memcpy(kvp, buffer, TAG_HEADER_SIZE);
-      kvp += header_size;
-      struct raw_tag raw;
-      buffer =
-          decode_tag(&raw, (char *)buffer, tag_header_size - TAG_HEADER_SIZE);
-      memcpy(kvp, raw.key, (size_t)raw.key_len + raw.value_len);
-      kvp += raw.key_len + raw.value_len;
-    }
-  } else {
-    memcpy(tags->kvm, buffer, tags->kvm_used);
-  }
-}
-
-census_tag_set *census_tag_set_decode(const char *buffer, size_t size,
-                                      const char *bin_buffer, size_t bin_size) {
-  census_tag_set *new_ts = gpr_malloc(sizeof(census_tag_set));
-  memset(&new_ts->tags[LOCAL_TAGS], 0, sizeof(struct tag_set));
-  if (buffer == NULL) {
-    memset(&new_ts->tags[PROPAGATED_TAGS], 0, sizeof(struct tag_set));
-  } else {
-    tag_set_decode(&new_ts->tags[PROPAGATED_TAGS], buffer, size);
-  }
-  if (bin_buffer == NULL) {
-    memset(&new_ts->tags[PROPAGATED_BINARY_TAGS], 0, sizeof(struct tag_set));
-  } else {
-    tag_set_decode(&new_ts->tags[PROPAGATED_BINARY_TAGS], bin_buffer, bin_size);
-  }
-  memset(&new_ts->status, 0, sizeof(new_ts->status));
-  new_ts->status.n_propagated_tags = new_ts->tags[PROPAGATED_TAGS].ntags;
-  new_ts->status.n_propagated_binary_tags =
-      new_ts->tags[PROPAGATED_BINARY_TAGS].ntags;
-  // TODO(aveitch): check that BINARY flag is correct for each type.
-  return new_ts;
-}
diff --git a/src/python/grpcio/grpc_core_dependencies.py b/src/python/grpcio/grpc_core_dependencies.py
index 1b2490e9ff..6e89c87436 100644
--- a/src/python/grpcio/grpc_core_dependencies.py
+++ b/src/python/grpcio/grpc_core_dependencies.py
@@ -225,7 +225,6 @@ CORE_SOURCE_FILES = [
   'src/core/census/initialize.c',
   'src/core/census/operation.c',
   'src/core/census/placeholders.c',
-  'src/core/census/tag_set.c',
   'src/core/census/tracing.c',
   'src/boringssl/err_data.c',
   'third_party/boringssl/crypto/aes/aes.c',
diff --git a/src/ruby/ext/grpc/rb_grpc_imports.generated.c b/src/ruby/ext/grpc/rb_grpc_imports.generated.c
index a278b2ba99..d4ddb734c0 100644
--- a/src/ruby/ext/grpc/rb_grpc_imports.generated.c
+++ b/src/ruby/ext/grpc/rb_grpc_imports.generated.c
@@ -41,7 +41,14 @@ census_initialize_type census_initialize_import;
 census_shutdown_type census_shutdown_import;
 census_supported_type census_supported_import;
 census_enabled_type census_enabled_import;
-census_context_serialize_type census_context_serialize_import;
+census_context_create_type census_context_create_import;
+census_context_destroy_type census_context_destroy_import;
+census_context_get_status_type census_context_get_status_import;
+census_context_initialize_iterator_type census_context_initialize_iterator_import;
+census_context_next_tag_type census_context_next_tag_import;
+census_context_get_tag_type census_context_get_tag_import;
+census_context_encode_type census_context_encode_import;
+census_context_decode_type census_context_decode_import;
 census_trace_mask_type census_trace_mask_import;
 census_set_trace_mask_type census_set_trace_mask_import;
 census_start_rpc_op_timestamp_type census_start_rpc_op_timestamp_import;
@@ -54,15 +61,6 @@ census_trace_print_type census_trace_print_import;
 census_trace_scan_start_type census_trace_scan_start_import;
 census_get_trace_record_type census_get_trace_record_import;
 census_trace_scan_end_type census_trace_scan_end_import;
-census_tag_set_create_type census_tag_set_create_import;
-census_tag_set_destroy_type census_tag_set_destroy_import;
-census_tag_set_get_create_status_type census_tag_set_get_create_status_import;
-census_tag_set_initialize_iterator_type census_tag_set_initialize_iterator_import;
-census_tag_set_next_tag_type census_tag_set_next_tag_import;
-census_tag_set_get_tag_by_key_type census_tag_set_get_tag_by_key_import;
-census_tag_set_encode_type census_tag_set_encode_import;
-census_tag_set_decode_type census_tag_set_decode_import;
-census_context_tag_set_type census_context_tag_set_import;
 census_record_values_type census_record_values_import;
 census_view_create_type census_view_create_import;
 census_view_delete_type census_view_delete_import;
@@ -303,7 +301,14 @@ void grpc_rb_load_imports(HMODULE library) {
   census_shutdown_import = (census_shutdown_type) GetProcAddress(library, "census_shutdown");
   census_supported_import = (census_supported_type) GetProcAddress(library, "census_supported");
   census_enabled_import = (census_enabled_type) GetProcAddress(library, "census_enabled");
-  census_context_serialize_import = (census_context_serialize_type) GetProcAddress(library, "census_context_serialize");
+  census_context_create_import = (census_context_create_type) GetProcAddress(library, "census_context_create");
+  census_context_destroy_import = (census_context_destroy_type) GetProcAddress(library, "census_context_destroy");
+  census_context_get_status_import = (census_context_get_status_type) GetProcAddress(library, "census_context_get_status");
+  census_context_initialize_iterator_import = (census_context_initialize_iterator_type) GetProcAddress(library, "census_context_initialize_iterator");
+  census_context_next_tag_import = (census_context_next_tag_type) GetProcAddress(library, "census_context_next_tag");
+  census_context_get_tag_import = (census_context_get_tag_type) GetProcAddress(library, "census_context_get_tag");
+  census_context_encode_import = (census_context_encode_type) GetProcAddress(library, "census_context_encode");
+  census_context_decode_import = (census_context_decode_type) GetProcAddress(library, "census_context_decode");
   census_trace_mask_import = (census_trace_mask_type) GetProcAddress(library, "census_trace_mask");
   census_set_trace_mask_import = (census_set_trace_mask_type) GetProcAddress(library, "census_set_trace_mask");
   census_start_rpc_op_timestamp_import = (census_start_rpc_op_timestamp_type) GetProcAddress(library, "census_start_rpc_op_timestamp");
@@ -316,15 +321,6 @@ void grpc_rb_load_imports(HMODULE library) {
   census_trace_scan_start_import = (census_trace_scan_start_type) GetProcAddress(library, "census_trace_scan_start");
   census_get_trace_record_import = (census_get_trace_record_type) GetProcAddress(library, "census_get_trace_record");
   census_trace_scan_end_import = (census_trace_scan_end_type) GetProcAddress(library, "census_trace_scan_end");
-  census_tag_set_create_import = (census_tag_set_create_type) GetProcAddress(library, "census_tag_set_create");
-  census_tag_set_destroy_import = (census_tag_set_destroy_type) GetProcAddress(library, "census_tag_set_destroy");
-  census_tag_set_get_create_status_import = (census_tag_set_get_create_status_type) GetProcAddress(library, "census_tag_set_get_create_status");
-  census_tag_set_initialize_iterator_import = (census_tag_set_initialize_iterator_type) GetProcAddress(library, "census_tag_set_initialize_iterator");
-  census_tag_set_next_tag_import = (census_tag_set_next_tag_type) GetProcAddress(library, "census_tag_set_next_tag");
-  census_tag_set_get_tag_by_key_import = (census_tag_set_get_tag_by_key_type) GetProcAddress(library, "census_tag_set_get_tag_by_key");
-  census_tag_set_encode_import = (census_tag_set_encode_type) GetProcAddress(library, "census_tag_set_encode");
-  census_tag_set_decode_import = (census_tag_set_decode_type) GetProcAddress(library, "census_tag_set_decode");
-  census_context_tag_set_import = (census_context_tag_set_type) GetProcAddress(library, "census_context_tag_set");
   census_record_values_import = (census_record_values_type) GetProcAddress(library, "census_record_values");
   census_view_create_import = (census_view_create_type) GetProcAddress(library, "census_view_create");
   census_view_delete_import = (census_view_delete_type) GetProcAddress(library, "census_view_delete");
diff --git a/src/ruby/ext/grpc/rb_grpc_imports.generated.h b/src/ruby/ext/grpc/rb_grpc_imports.generated.h
index 3e29496a43..45e9b47574 100644
--- a/src/ruby/ext/grpc/rb_grpc_imports.generated.h
+++ b/src/ruby/ext/grpc/rb_grpc_imports.generated.h
@@ -73,9 +73,30 @@ extern census_supported_type census_supported_import;
 typedef int(*census_enabled_type)(void);
 extern census_enabled_type census_enabled_import;
 #define census_enabled census_enabled_import
-typedef size_t(*census_context_serialize_type)(const census_context *context, char *buffer, size_t buf_size);
-extern census_context_serialize_type census_context_serialize_import;
-#define census_context_serialize census_context_serialize_import
+typedef census_context *(*census_context_create_type)(const census_context *base, const census_tag *tags, int ntags, census_context_status const **status);
+extern census_context_create_type census_context_create_import;
+#define census_context_create census_context_create_import
+typedef void(*census_context_destroy_type)(census_context *context);
+extern census_context_destroy_type census_context_destroy_import;
+#define census_context_destroy census_context_destroy_import
+typedef const census_context_status *(*census_context_get_status_type)(const census_context *context);
+extern census_context_get_status_type census_context_get_status_import;
+#define census_context_get_status census_context_get_status_import
+typedef void(*census_context_initialize_iterator_type)(const census_context *context, census_context_iterator *iterator);
+extern census_context_initialize_iterator_type census_context_initialize_iterator_import;
+#define census_context_initialize_iterator census_context_initialize_iterator_import
+typedef int(*census_context_next_tag_type)(census_context_iterator *iterator, census_tag *tag);
+extern census_context_next_tag_type census_context_next_tag_import;
+#define census_context_next_tag census_context_next_tag_import
+typedef int(*census_context_get_tag_type)(const census_context *context, const char *key, census_tag *tag);
+extern census_context_get_tag_type census_context_get_tag_import;
+#define census_context_get_tag census_context_get_tag_import
+typedef char *(*census_context_encode_type)(const census_context *context, char *buffer, size_t buf_size, size_t *print_buf_size, size_t *bin_buf_size);
+extern census_context_encode_type census_context_encode_import;
+#define census_context_encode census_context_encode_import
+typedef census_context *(*census_context_decode_type)(const char *buffer, size_t size, const char *bin_buffer, size_t bin_size);
+extern census_context_decode_type census_context_decode_import;
+#define census_context_decode census_context_decode_import
 typedef int(*census_trace_mask_type)(const census_context *context);
 extern census_trace_mask_type census_trace_mask_import;
 #define census_trace_mask census_trace_mask_import
@@ -112,37 +133,10 @@ extern census_get_trace_record_type census_get_trace_record_import;
 typedef void(*census_trace_scan_end_type)();
 extern census_trace_scan_end_type census_trace_scan_end_import;
 #define census_trace_scan_end census_trace_scan_end_import
-typedef census_tag_set *(*census_tag_set_create_type)(const census_tag_set *base, const census_tag *tags, int ntags, census_tag_set_create_status const **status);
-extern census_tag_set_create_type census_tag_set_create_import;
-#define census_tag_set_create census_tag_set_create_import
-typedef void(*census_tag_set_destroy_type)(census_tag_set *tags);
-extern census_tag_set_destroy_type census_tag_set_destroy_import;
-#define census_tag_set_destroy census_tag_set_destroy_import
-typedef const census_tag_set_create_status *(*census_tag_set_get_create_status_type)(const census_tag_set *tags);
-extern census_tag_set_get_create_status_type census_tag_set_get_create_status_import;
-#define census_tag_set_get_create_status census_tag_set_get_create_status_import
-typedef void(*census_tag_set_initialize_iterator_type)(const census_tag_set *tags, census_tag_set_iterator *iterator);
-extern census_tag_set_initialize_iterator_type census_tag_set_initialize_iterator_import;
-#define census_tag_set_initialize_iterator census_tag_set_initialize_iterator_import
-typedef int(*census_tag_set_next_tag_type)(census_tag_set_iterator *iterator, census_tag *tag);
-extern census_tag_set_next_tag_type census_tag_set_next_tag_import;
-#define census_tag_set_next_tag census_tag_set_next_tag_import
-typedef int(*census_tag_set_get_tag_by_key_type)(const census_tag_set *tags, const char *key, census_tag *tag);
-extern census_tag_set_get_tag_by_key_type census_tag_set_get_tag_by_key_import;
-#define census_tag_set_get_tag_by_key census_tag_set_get_tag_by_key_import
-typedef char *(*census_tag_set_encode_type)(const census_tag_set *tags, char *buffer, size_t buf_size, size_t *print_buf_size, size_t *bin_buf_size);
-extern census_tag_set_encode_type census_tag_set_encode_import;
-#define census_tag_set_encode census_tag_set_encode_import
-typedef census_tag_set *(*census_tag_set_decode_type)(const char *buffer, size_t size, const char *bin_buffer, size_t bin_size);
-extern census_tag_set_decode_type census_tag_set_decode_import;
-#define census_tag_set_decode census_tag_set_decode_import
-typedef census_tag_set *(*census_context_tag_set_type)(census_context *context);
-extern census_context_tag_set_type census_context_tag_set_import;
-#define census_context_tag_set census_context_tag_set_import
 typedef void(*census_record_values_type)(census_context *context, census_value *values, size_t nvalues);
 extern census_record_values_type census_record_values_import;
 #define census_record_values census_record_values_import
-typedef census_view *(*census_view_create_type)(uint32_t metric_id, const census_tag_set *tags, const census_aggregation *aggregations, size_t naggregations);
+typedef census_view *(*census_view_create_type)(uint32_t metric_id, const census_context *tags, const census_aggregation *aggregations, size_t naggregations);
 extern census_view_create_type census_view_create_import;
 #define census_view_create census_view_create_import
 typedef void(*census_view_delete_type)(census_view *view);
@@ -154,7 +148,7 @@ extern census_view_metric_type census_view_metric_import;
 typedef size_t(*census_view_naggregations_type)(const census_view *view);
 extern census_view_naggregations_type census_view_naggregations_import;
 #define census_view_naggregations census_view_naggregations_import
-typedef const census_tag_set *(*census_view_tags_type)(const census_view *view);
+typedef const census_context *(*census_view_tags_type)(const census_view *view);
 extern census_view_tags_type census_view_tags_import;
 #define census_view_tags census_view_tags_import
 typedef const census_aggregation *(*census_view_aggregrations_type)(const census_view *view);