Merge github.com:grpc/grpc into slice_with_exec_ctx

16 files changed, 537 insertions, 154 deletions

diff --git a/src/core/ext/client_channel/client_channel.c b/src/core/ext/client_channel/client_channel.c
index 8f0c856afe..0e2ec476fe 100644
--- a/src/core/ext/client_channel/client_channel.c
+++ b/src/core/ext/client_channel/client_channel.c
@@ -56,7 +56,7 @@
 #include "src/core/lib/transport/connectivity_state.h"
 #include "src/core/lib/transport/metadata.h"
 #include "src/core/lib/transport/metadata_batch.h"
-#include "src/core/lib/transport/method_config.h"
+#include "src/core/lib/transport/service_config.h"
 #include "src/core/lib/transport/static_metadata.h"
 
 /* Client channel implementation */
@@ -82,34 +82,65 @@ static void *method_parameters_copy(void *value) {
   return new_value;
 }
 
-static int method_parameters_cmp(void *value1, void *value2) {
-  const method_parameters *v1 = value1;
-  const method_parameters *v2 = value2;
-  const int retval = gpr_time_cmp(v1->timeout, v2->timeout);
-  if (retval != 0) return retval;
-  if (v1->wait_for_ready > v2->wait_for_ready) return 1;
-  if (v1->wait_for_ready < v2->wait_for_ready) return -1;
-  return 0;
-}
-
-static void method_parameters_del(grpc_exec_ctx *exec_ctx, void *p) {
+static void method_parameters_free(grpc_exec_ctx *exec_ctx, void *p) {
   gpr_free(p);
 }
 
 static const grpc_mdstr_hash_table_vtable method_parameters_vtable = {
-    method_parameters_del, method_parameters_copy, method_parameters_cmp};
-
-static void *method_config_convert_value(
-    const grpc_method_config *method_config) {
+    method_parameters_free, method_parameters_copy};
+
+static void *method_parameters_create_from_json(const grpc_json *json) {
+  wait_for_ready_value wait_for_ready = WAIT_FOR_READY_UNSET;
+  gpr_timespec timeout = {0, 0, GPR_TIMESPAN};
+  for (grpc_json *field = json->child; field != NULL; field = field->next) {
+    if (field->key == NULL) continue;
+    if (strcmp(field->key, "waitForReady") == 0) {
+      if (wait_for_ready != WAIT_FOR_READY_UNSET) return NULL;  // Duplicate.
+      if (field->type != GRPC_JSON_TRUE && field->type != GRPC_JSON_FALSE) {
+        return NULL;
+      }
+      wait_for_ready = field->type == GRPC_JSON_TRUE ? WAIT_FOR_READY_TRUE
+                                                     : WAIT_FOR_READY_FALSE;
+    } else if (strcmp(field->key, "timeout") == 0) {
+      if (timeout.tv_sec > 0 || timeout.tv_nsec > 0) return NULL;  // Duplicate.
+      if (field->type != GRPC_JSON_STRING) return NULL;
+      size_t len = strlen(field->value);
+      if (field->value[len - 1] != 's') return NULL;
+      char *buf = gpr_strdup(field->value);
+      buf[len - 1] = '\0';  // Remove trailing 's'.
+      char *decimal_point = strchr(buf, '.');
+      if (decimal_point != NULL) {
+        *decimal_point = '\0';
+        timeout.tv_nsec = gpr_parse_nonnegative_int(decimal_point + 1);
+        if (timeout.tv_nsec == -1) {
+          gpr_free(buf);
+          return NULL;
+        }
+        // There should always be exactly 3, 6, or 9 fractional digits.
+        int multiplier = 1;
+        switch (strlen(decimal_point + 1)) {
+          case 9:
+            break;
+          case 6:
+            multiplier *= 1000;
+            break;
+          case 3:
+            multiplier *= 1000000;
+            break;
+          default:  // Unsupported number of digits.
+            gpr_free(buf);
+            return NULL;
+        }
+        timeout.tv_nsec *= multiplier;
+      }
+      timeout.tv_sec = gpr_parse_nonnegative_int(buf);
+      if (timeout.tv_sec == -1) return NULL;
+      gpr_free(buf);
+    }
+  }
   method_parameters *value = gpr_malloc(sizeof(method_parameters));
-  const gpr_timespec *timeout = grpc_method_config_get_timeout(method_config);
-  value->timeout = timeout != NULL ? *timeout : gpr_time_0(GPR_TIMESPAN);
-  const bool *wait_for_ready =
-      grpc_method_config_get_wait_for_ready(method_config);
-  value->wait_for_ready =
-      wait_for_ready == NULL
-          ? WAIT_FOR_READY_UNSET
-          : (wait_for_ready ? WAIT_FOR_READY_TRUE : WAIT_FOR_READY_FALSE);
+  value->timeout = timeout;
+  value->wait_for_ready = wait_for_ready;
   return value;
 }
 
@@ -130,6 +161,8 @@ typedef struct client_channel_channel_data {
   /** currently active load balancer */
   char *lb_policy_name;
   grpc_lb_policy *lb_policy;
+  /** service config in JSON form */
+  char *service_config_json;
   /** maps method names to method_parameters structs */
   grpc_mdstr_hash_table *method_params_table;
   /** incoming resolver result - set by resolver.next() */
@@ -236,15 +269,12 @@ static void on_resolver_result_changed(grpc_exec_ctx *exec_ctx, void *arg,
   grpc_connectivity_state state = GRPC_CHANNEL_TRANSIENT_FAILURE;
   bool exit_idle = false;
   grpc_error *state_error = GRPC_ERROR_CREATE("No load balancing policy");
+  char *service_config_json = NULL;
 
   if (chand->resolver_result != NULL) {
-    grpc_lb_policy_args lb_policy_args;
-    lb_policy_args.args = chand->resolver_result;
-    lb_policy_args.client_channel_factory = chand->client_channel_factory;
-
     // Find LB policy name.
     const grpc_arg *channel_arg =
-        grpc_channel_args_find(lb_policy_args.args, GRPC_ARG_LB_POLICY_NAME);
+        grpc_channel_args_find(chand->resolver_result, GRPC_ARG_LB_POLICY_NAME);
     if (channel_arg != NULL) {
       GPR_ASSERT(channel_arg->type == GRPC_ARG_STRING);
       lb_policy_name = channel_arg->value.string;
@@ -253,7 +283,7 @@ static void on_resolver_result_changed(grpc_exec_ctx *exec_ctx, void *arg,
     // assume that we should use the grpclb policy, regardless of what the
     // resolver actually specified.
     channel_arg =
-        grpc_channel_args_find(lb_policy_args.args, GRPC_ARG_LB_ADDRESSES);
+        grpc_channel_args_find(chand->resolver_result, GRPC_ARG_LB_ADDRESSES);
     if (channel_arg != NULL) {
       GPR_ASSERT(channel_arg->type == GRPC_ARG_POINTER);
       grpc_lb_addresses *addresses = channel_arg->value.pointer.p;
@@ -278,7 +308,10 @@ static void on_resolver_result_changed(grpc_exec_ctx *exec_ctx, void *arg,
     // Use pick_first if nothing was specified and we didn't select grpclb
     // above.
     if (lb_policy_name == NULL) lb_policy_name = "pick_first";
-
+    // Instantiate LB policy.
+    grpc_lb_policy_args lb_policy_args;
+    lb_policy_args.args = chand->resolver_result;
+    lb_policy_args.client_channel_factory = chand->client_channel_factory;
     lb_policy =
         grpc_lb_policy_create(exec_ctx, lb_policy_name, &lb_policy_args);
     if (lb_policy != NULL) {
@@ -287,13 +320,20 @@ static void on_resolver_result_changed(grpc_exec_ctx *exec_ctx, void *arg,
       state =
           grpc_lb_policy_check_connectivity(exec_ctx, lb_policy, &state_error);
     }
+    // Find service config.
     channel_arg =
-        grpc_channel_args_find(lb_policy_args.args, GRPC_ARG_SERVICE_CONFIG);
+        grpc_channel_args_find(chand->resolver_result, GRPC_ARG_SERVICE_CONFIG);
     if (channel_arg != NULL) {
-      GPR_ASSERT(channel_arg->type == GRPC_ARG_POINTER);
-      method_params_table = grpc_method_config_table_convert(
-          exec_ctx, (grpc_method_config_table *)channel_arg->value.pointer.p,
-          method_config_convert_value, &method_parameters_vtable);
+      GPR_ASSERT(channel_arg->type == GRPC_ARG_STRING);
+      service_config_json = gpr_strdup(channel_arg->value.string);
+      grpc_service_config *service_config =
+          grpc_service_config_create(service_config_json);
+      if (service_config != NULL) {
+        method_params_table = grpc_service_config_create_method_config_table(
+            exec_ctx, service_config, method_parameters_create_from_json,
+            &method_parameters_vtable);
+        grpc_service_config_destroy(service_config);
+      }
     }
     // Before we clean up, save a copy of lb_policy_name, since it might
     // be pointing to data inside chand->resolver_result.
@@ -315,6 +355,10 @@ static void on_resolver_result_changed(grpc_exec_ctx *exec_ctx, void *arg,
   }
   old_lb_policy = chand->lb_policy;
   chand->lb_policy = lb_policy;
+  if (service_config_json != NULL) {
+    gpr_free(chand->service_config_json);
+    chand->service_config_json = service_config_json;
+  }
   if (chand->method_params_table != NULL) {
     grpc_mdstr_hash_table_unref(exec_ctx, chand->method_params_table);
   }
@@ -450,6 +494,11 @@ static void cc_get_channel_info(grpc_exec_ctx *exec_ctx,
                                 ? NULL
                                 : gpr_strdup(chand->lb_policy_name);
   }
+  if (info->service_config_json != NULL) {
+    *info->service_config_json = chand->service_config_json == NULL
+                                     ? NULL
+                                     : gpr_strdup(chand->service_config_json);
+  }
   gpr_mu_unlock(&chand->mu);
 }
 
@@ -493,6 +542,7 @@ static void cc_destroy_channel_elem(grpc_exec_ctx *exec_ctx,
     GRPC_LB_POLICY_UNREF(exec_ctx, chand->lb_policy, "channel");
   }
   gpr_free(chand->lb_policy_name);
+  gpr_free(chand->service_config_json);
   if (chand->method_params_table != NULL) {
     grpc_mdstr_hash_table_unref(exec_ctx, chand->method_params_table);
   }
diff --git a/src/core/ext/client_channel/lb_policy_registry.c b/src/core/ext/client_channel/lb_policy_registry.c
index f46a721f9d..90c149d947 100644
--- a/src/core/ext/client_channel/lb_policy_registry.c
+++ b/src/core/ext/client_channel/lb_policy_registry.c
@@ -35,6 +35,8 @@
 
 #include <string.h>
 
+#include "src/core/lib/support/string.h"
+
 #define MAX_POLICIES 10
 
 static grpc_lb_policy_factory *g_all_of_the_lb_policies[MAX_POLICIES];
@@ -52,8 +54,8 @@ void grpc_lb_policy_registry_shutdown(void) {
 void grpc_register_lb_policy(grpc_lb_policy_factory *factory) {
   int i;
   for (i = 0; i < g_number_of_lb_policies; i++) {
-    GPR_ASSERT(0 != strcmp(factory->vtable->name,
-                           g_all_of_the_lb_policies[i]->vtable->name));
+    GPR_ASSERT(0 != gpr_stricmp(factory->vtable->name,
+                                g_all_of_the_lb_policies[i]->vtable->name));
   }
   GPR_ASSERT(g_number_of_lb_policies != MAX_POLICIES);
   grpc_lb_policy_factory_ref(factory);
@@ -66,7 +68,7 @@ static grpc_lb_policy_factory *lookup_factory(const char *name) {
   if (name == NULL) return NULL;
 
   for (i = 0; i < g_number_of_lb_policies; i++) {
-    if (0 == strcmp(name, g_all_of_the_lb_policies[i]->vtable->name)) {
+    if (0 == gpr_stricmp(name, g_all_of_the_lb_policies[i]->vtable->name)) {
       return g_all_of_the_lb_policies[i];
     }
   }
diff --git a/src/core/ext/lb_policy/grpclb/grpclb.c b/src/core/ext/lb_policy/grpclb/grpclb.c
index 4bca8def39..5760b0958d 100644
--- a/src/core/ext/lb_policy/grpclb/grpclb.c
+++ b/src/core/ext/lb_policy/grpclb/grpclb.c
@@ -187,14 +187,20 @@ static void wrapped_rr_closure(grpc_exec_ctx *exec_ctx, void *arg,
      * addresses failed to connect). There won't be any user_data/token
      * available */
     if (wc_arg->target != NULL) {
-      GPR_ASSERT(wc_arg->lb_token != NULL);
-      initial_metadata_add_lb_token(wc_arg->initial_metadata,
-                                    wc_arg->lb_token_mdelem_storage,
-                                    GRPC_MDELEM_REF(wc_arg->lb_token));
+      if (wc_arg->lb_token != NULL) {
+        initial_metadata_add_lb_token(wc_arg->initial_metadata,
+                                      wc_arg->lb_token_mdelem_storage,
+                                      GRPC_MDELEM_REF(wc_arg->lb_token));
+      } else {
+        gpr_log(GPR_ERROR,
+                "No LB token for connected subchannel pick %p (from RR "
+                "instance %p).",
+                (void *)*wc_arg->target, (void *)wc_arg->rr_policy);
+        abort();
+      }
     }
     if (grpc_lb_glb_trace) {
-      gpr_log(GPR_INFO, "Unreffing RR (0x%" PRIxPTR ")",
-              (intptr_t)wc_arg->rr_policy);
+      gpr_log(GPR_INFO, "Unreffing RR %p", (void *)wc_arg->rr_policy);
     }
     GRPC_LB_POLICY_UNREF(exec_ctx, wc_arg->rr_policy, "wrapped_rr_closure");
   }
@@ -412,7 +418,7 @@ static void parse_server(const grpc_grpclb_server *server,
 }
 
 /* Returns addresses extracted from \a serverlist. */
-static grpc_lb_addresses *process_serverlist(
+static grpc_lb_addresses *process_serverlist_locked(
     grpc_exec_ctx *exec_ctx, const grpc_grpclb_serverlist *serverlist) {
   size_t num_valid = 0;
   /* first pass: count how many are valid in order to allocate the necessary
@@ -452,10 +458,12 @@ static grpc_lb_addresses *process_serverlist(
       user_data = grpc_mdelem_from_metadata_strings(
           exec_ctx, GRPC_MDSTR_LB_TOKEN, lb_token_mdstr);
     } else {
-      gpr_log(GPR_ERROR,
+      char *uri = grpc_sockaddr_to_uri(&addr);
+      gpr_log(GPR_INFO,
               "Missing LB token for backend address '%s'. The empty token will "
               "be used instead",
-              grpc_sockaddr_to_uri(&addr));
+              uri);
+      gpr_free(uri);
       user_data = GRPC_MDELEM_LB_TOKEN_EMPTY;
     }
 
@@ -509,7 +517,8 @@ static grpc_lb_policy *create_rr_locked(
   grpc_lb_policy_args args;
   memset(&args, 0, sizeof(args));
   args.client_channel_factory = glb_policy->cc_factory;
-  grpc_lb_addresses *addresses = process_serverlist(exec_ctx, serverlist);
+  grpc_lb_addresses *addresses =
+      process_serverlist_locked(exec_ctx, serverlist);
 
   // Replace the LB addresses in the channel args that we pass down to
   // the subchannel.
@@ -769,7 +778,6 @@ static void glb_shutdown(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
    * while holding glb_policy->mu: lb_on_server_status_received, invoked due to
    * the cancel, needs to acquire that same lock */
   grpc_call *lb_call = glb_policy->lb_call;
-  glb_policy->lb_call = NULL;
   gpr_mu_unlock(&glb_policy->mu);
 
   /* glb_policy->lb_call and this local lb_call must be consistent at this point
diff --git a/src/core/lib/channel/message_size_filter.c b/src/core/lib/channel/message_size_filter.c
index 1655d843d5..b5938b4342 100644
--- a/src/core/lib/channel/message_size_filter.c
+++ b/src/core/lib/channel/message_size_filter.c
@@ -39,7 +39,8 @@
 #include <grpc/support/string_util.h>
 
 #include "src/core/lib/channel/channel_args.h"
-#include "src/core/lib/transport/method_config.h"
+#include "src/core/lib/support/string.h"
+#include "src/core/lib/transport/service_config.h"
 
 #define DEFAULT_MAX_SEND_MESSAGE_LENGTH -1  // Unlimited.
 // The protobuf library will (by default) start warning at 100 megs.
@@ -56,32 +57,33 @@ static void* message_size_limits_copy(void* value) {
   return new_value;
 }
 
-static int message_size_limits_cmp(void* value1, void* value2) {
-  const message_size_limits* v1 = value1;
-  const message_size_limits* v2 = value2;
-  if (v1->max_send_size > v2->max_send_size) return 1;
-  if (v1->max_send_size < v2->max_send_size) return -1;
-  if (v1->max_recv_size > v2->max_recv_size) return 1;
-  if (v1->max_recv_size < v2->max_recv_size) return -1;
-  return 0;
+static void message_size_limits_free(grpc_exec_ctx* exec_ctx, void* value) {
+  gpr_free(value);
 }
 
-static void free_mem(grpc_exec_ctx* exec_ctx, void* p) { gpr_free(p); }
-
 static const grpc_mdstr_hash_table_vtable message_size_limits_vtable = {
-    free_mem, message_size_limits_copy, message_size_limits_cmp};
+    message_size_limits_free, message_size_limits_copy};
 
-static void* method_config_convert_value(
-    const grpc_method_config* method_config) {
+static void* message_size_limits_create_from_json(const grpc_json* json) {
+  int max_request_message_bytes = -1;
+  int max_response_message_bytes = -1;
+  for (grpc_json* field = json->child; field != NULL; field = field->next) {
+    if (field->key == NULL) continue;
+    if (strcmp(field->key, "maxRequestMessageBytes") == 0) {
+      if (max_request_message_bytes >= 0) return NULL;  // Duplicate.
+      if (field->type != GRPC_JSON_STRING) return NULL;
+      max_request_message_bytes = gpr_parse_nonnegative_int(field->value);
+      if (max_request_message_bytes == -1) return NULL;
+    } else if (strcmp(field->key, "maxResponseMessageBytes") == 0) {
+      if (max_response_message_bytes >= 0) return NULL;  // Duplicate.
+      if (field->type != GRPC_JSON_STRING) return NULL;
+      max_response_message_bytes = gpr_parse_nonnegative_int(field->value);
+      if (max_response_message_bytes == -1) return NULL;
+    }
+  }
   message_size_limits* value = gpr_malloc(sizeof(message_size_limits));
-  const int32_t* max_request_message_bytes =
-      grpc_method_config_get_max_request_message_bytes(method_config);
-  value->max_send_size =
-      max_request_message_bytes != NULL ? *max_request_message_bytes : -1;
-  const int32_t* max_response_message_bytes =
-      grpc_method_config_get_max_response_message_bytes(method_config);
-  value->max_recv_size =
-      max_response_message_bytes != NULL ? *max_response_message_bytes : -1;
+  value->max_send_size = max_request_message_bytes;
+  value->max_recv_size = max_response_message_bytes;
   return value;
 }
 
@@ -225,10 +227,16 @@ static void init_channel_elem(grpc_exec_ctx* exec_ctx,
   const grpc_arg* channel_arg =
       grpc_channel_args_find(args->channel_args, GRPC_ARG_SERVICE_CONFIG);
   if (channel_arg != NULL) {
-    GPR_ASSERT(channel_arg->type == GRPC_ARG_POINTER);
-    chand->method_limit_table = grpc_method_config_table_convert(
-        exec_ctx, (grpc_method_config_table*)channel_arg->value.pointer.p,
-        method_config_convert_value, &message_size_limits_vtable);
+    GPR_ASSERT(channel_arg->type == GRPC_ARG_STRING);
+    grpc_service_config* service_config =
+        grpc_service_config_create(channel_arg->value.string);
+    if (service_config != NULL) {
+      chand->method_limit_table =
+          grpc_service_config_create_method_config_table(
+              exec_ctx, service_config, message_size_limits_create_from_json,
+              &message_size_limits_vtable);
+      grpc_service_config_destroy(service_config);
+    }
   }
 }
 
diff --git a/src/core/lib/json/json.c b/src/core/lib/json/json.c
index 5b583a1f2e..48b13686d7 100644
--- a/src/core/lib/json/json.c
+++ b/src/core/lib/json/json.c
@@ -37,15 +37,15 @@
 
 #include "src/core/lib/json/json.h"
 
-grpc_json *grpc_json_create(grpc_json_type type) {
-  grpc_json *json = gpr_malloc(sizeof(*json));
+grpc_json* grpc_json_create(grpc_json_type type) {
+  grpc_json* json = gpr_malloc(sizeof(*json));
   memset(json, 0, sizeof(*json));
   json->type = type;
 
   return json;
 }
 
-void grpc_json_destroy(grpc_json *json) {
+void grpc_json_destroy(grpc_json* json) {
   while (json->child) {
     grpc_json_destroy(json->child);
   }
diff --git a/src/core/lib/json/json.h b/src/core/lib/json/json.h
index 681df4bb77..7111db0b52 100644
--- a/src/core/lib/json/json.h
+++ b/src/core/lib/json/json.h
@@ -42,14 +42,14 @@
  * are not owned by it.
  */
 typedef struct grpc_json {
-  struct grpc_json *next;
-  struct grpc_json *prev;
-  struct grpc_json *child;
-  struct grpc_json *parent;
+  struct grpc_json* next;
+  struct grpc_json* prev;
+  struct grpc_json* child;
+  struct grpc_json* parent;
 
   grpc_json_type type;
-  const char *key;
-  const char *value;
+  const char* key;
+  const char* value;
 } grpc_json;
 
 /* The next two functions are going to parse the input string, and
@@ -65,8 +65,8 @@ typedef struct grpc_json {
  *
  * Delete the allocated tree afterward using grpc_json_destroy().
  */
-grpc_json *grpc_json_parse_string_with_len(char *input, size_t size);
-grpc_json *grpc_json_parse_string(char *input);
+grpc_json* grpc_json_parse_string_with_len(char* input, size_t size);
+grpc_json* grpc_json_parse_string(char* input);
 
 /* This function will create a new string using gpr_realloc, and will
  * deserialize the grpc_json tree into it. It'll be zero-terminated,
@@ -76,13 +76,13 @@ grpc_json *grpc_json_parse_string(char *input);
  * If indent is 0, then newlines will be suppressed as well, and the
  * output will be condensed at its maximum.
  */
-char *grpc_json_dump_to_string(grpc_json *json, int indent);
+char* grpc_json_dump_to_string(grpc_json* json, int indent);
 
 /* Use these to create or delete a grpc_json object.
  * Deletion is recursive. We will not attempt to free any of the strings
  * in any of the objects of that tree.
  */
-grpc_json *grpc_json_create(grpc_json_type type);
-void grpc_json_destroy(grpc_json *json);
+grpc_json* grpc_json_create(grpc_json_type type);
+void grpc_json_destroy(grpc_json* json);
 
 #endif /* GRPC_CORE_LIB_JSON_JSON_H */
diff --git a/src/core/lib/support/string.c b/src/core/lib/support/string.c
index 85b915f118..0dc55c2ca3 100644
--- a/src/core/lib/support/string.c
+++ b/src/core/lib/support/string.c
@@ -34,7 +34,9 @@
 #include "src/core/lib/support/string.h"
 
 #include <ctype.h>
+#include <limits.h>
 #include <stddef.h>
+#include <stdlib.h>
 #include <string.h>
 
 #include <grpc/support/alloc.h>
@@ -189,6 +191,13 @@ int int64_ttoa(int64_t value, char *string) {
   return i;
 }
 
+int gpr_parse_nonnegative_int(const char *value) {
+  char *end;
+  long result = strtol(value, &end, 0);
+  if (*end != '\0' || result < 0 || result > INT_MAX) return -1;
+  return (int)result;
+}
+
 char *gpr_leftpad(const char *str, char flag, size_t length) {
   const size_t str_length = strlen(str);
   const size_t out_length = str_length > length ? str_length : length;
diff --git a/src/core/lib/support/string.h b/src/core/lib/support/string.h
index 81a12ae476..43ab4dc1be 100644
--- a/src/core/lib/support/string.h
+++ b/src/core/lib/support/string.h
@@ -77,6 +77,9 @@ NOTE: This function ensures sufficient bit width even on Win x64,
 where long is 32bit is size.*/
 int int64_ttoa(int64_t value, char *output);
 
+// Parses a non-negative number from a value string.  Returns -1 on error.
+int gpr_parse_nonnegative_int(const char *value);
+
 /* Reverse a run of bytes */
 void gpr_reverse_bytes(char *str, int len);
 
diff --git a/src/core/lib/transport/mdstr_hash_table.c b/src/core/lib/transport/mdstr_hash_table.c
index a3f6bde516..2791bf653b 100644
--- a/src/core/lib/transport/mdstr_hash_table.c
+++ b/src/core/lib/transport/mdstr_hash_table.c
@@ -41,7 +41,6 @@
 
 struct grpc_mdstr_hash_table {
   gpr_refcount refs;
-  size_t num_entries;
   size_t size;
   grpc_mdstr_hash_table_entry* entries;
 };
@@ -77,7 +76,6 @@ grpc_mdstr_hash_table* grpc_mdstr_hash_table_create(
   grpc_mdstr_hash_table* table = gpr_malloc(sizeof(*table));
   memset(table, 0, sizeof(*table));
   gpr_ref_init(&table->refs, 1);
-  table->num_entries = num_entries;
   // Quadratic probing gets best performance when the table is no more
   // than half full.
   table->size = num_entries * 2;
@@ -96,8 +94,8 @@ grpc_mdstr_hash_table* grpc_mdstr_hash_table_ref(grpc_mdstr_hash_table* table) {
   return table;
 }
 
-int grpc_mdstr_hash_table_unref(grpc_exec_ctx* exec_ctx,
-                                grpc_mdstr_hash_table* table) {
+void grpc_mdstr_hash_table_unref(grpc_exec_ctx* exec_ctx,
+                                 grpc_mdstr_hash_table* table) {
   if (table != NULL && gpr_unref(&table->refs)) {
     for (size_t i = 0; i < table->size; ++i) {
       grpc_mdstr_hash_table_entry* entry = &table->entries[i];
@@ -108,13 +106,7 @@ int grpc_mdstr_hash_table_unref(grpc_exec_ctx* exec_ctx,
     }
     gpr_free(table->entries);
     gpr_free(table);
-    return 1;
   }
-  return 0;
-}
-
-size_t grpc_mdstr_hash_table_num_entries(const grpc_mdstr_hash_table* table) {
-  return table->num_entries;
 }
 
 void* grpc_mdstr_hash_table_get(const grpc_mdstr_hash_table* table,
@@ -124,35 +116,3 @@ void* grpc_mdstr_hash_table_get(const grpc_mdstr_hash_table* table,
   if (idx == table->size) return NULL;  // Not found.
   return table->entries[idx].value;
 }
-
-int grpc_mdstr_hash_table_cmp(const grpc_mdstr_hash_table* table1,
-                              const grpc_mdstr_hash_table* table2) {
-  // Compare by num_entries.
-  if (table1->num_entries < table2->num_entries) return -1;
-  if (table1->num_entries > table2->num_entries) return 1;
-  for (size_t i = 0; i < table1->num_entries; ++i) {
-    grpc_mdstr_hash_table_entry* e1 = &table1->entries[i];
-    grpc_mdstr_hash_table_entry* e2 = &table2->entries[i];
-    // Compare keys by hash value.
-    if (e1->key->hash < e2->key->hash) return -1;
-    if (e1->key->hash > e2->key->hash) return 1;
-    // Compare by vtable (pointer equality).
-    if (e1->vtable < e2->vtable) return -1;
-    if (e1->vtable > e2->vtable) return 1;
-    // Compare values via vtable.
-    const int value_result = e1->vtable->compare_value(e1->value, e2->value);
-    if (value_result != 0) return value_result;
-  }
-  return 0;
-}
-
-void grpc_mdstr_hash_table_iterate(
-    const grpc_mdstr_hash_table* table,
-    void (*func)(const grpc_mdstr_hash_table_entry* entry, void* user_data),
-    void* user_data) {
-  for (size_t i = 0; i < table->size; ++i) {
-    if (table->entries[i].key != NULL) {
-      func(&table->entries[i], user_data);
-    }
-  }
-}
diff --git a/src/core/lib/transport/mdstr_hash_table.h b/src/core/lib/transport/mdstr_hash_table.h
index 45e5720063..57f497ee27 100644
--- a/src/core/lib/transport/mdstr_hash_table.h
+++ b/src/core/lib/transport/mdstr_hash_table.h
@@ -51,7 +51,6 @@ typedef struct grpc_mdstr_hash_table grpc_mdstr_hash_table;
 typedef struct grpc_mdstr_hash_table_vtable {
   void (*destroy_value)(grpc_exec_ctx* exec_ctx, void* value);
   void* (*copy_value)(void* value);
-  int (*compare_value)(void* value1, void* value2);
 } grpc_mdstr_hash_table_vtable;
 
 typedef struct grpc_mdstr_hash_table_entry {
@@ -67,27 +66,12 @@ grpc_mdstr_hash_table* grpc_mdstr_hash_table_create(
     size_t num_entries, grpc_mdstr_hash_table_entry* entries);
 
 grpc_mdstr_hash_table* grpc_mdstr_hash_table_ref(grpc_mdstr_hash_table* table);
-/** Returns 1 when \a table is destroyed. */
-int grpc_mdstr_hash_table_unref(grpc_exec_ctx* exec_ctx,
-                                grpc_mdstr_hash_table* table);
-
-/** Returns the number of entries in \a table. */
-size_t grpc_mdstr_hash_table_num_entries(const grpc_mdstr_hash_table* table);
+void grpc_mdstr_hash_table_unref(grpc_exec_ctx* exec_ctx,
+                                 grpc_mdstr_hash_table* table);
 
 /** Returns the value from \a table associated with \a key.
     Returns NULL if \a key is not found. */
 void* grpc_mdstr_hash_table_get(const grpc_mdstr_hash_table* table,
                                 const grpc_mdstr* key);
 
-/** Compares two hash tables.
-    The sort order is stable but undefined. */
-int grpc_mdstr_hash_table_cmp(const grpc_mdstr_hash_table* table1,
-                              const grpc_mdstr_hash_table* table2);
-
-/** Iterates over the entries in \a table, calling \a func for each entry. */
-void grpc_mdstr_hash_table_iterate(
-    const grpc_mdstr_hash_table* table,
-    void (*func)(const grpc_mdstr_hash_table_entry* entry, void* user_data),
-    void* user_data);
-
 #endif /* GRPC_CORE_LIB_TRANSPORT_MDSTR_HASH_TABLE_H */
diff --git a/src/core/lib/transport/service_config.c b/src/core/lib/transport/service_config.c
new file mode 100644
index 0000000000..552d3ec856
--- /dev/null
+++ b/src/core/lib/transport/service_config.c
@@ -0,0 +1,251 @@
+//
+// 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/lib/transport/service_config.h"
+
+#include <string.h>
+
+#include <grpc/impl/codegen/grpc_types.h>
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+#include <grpc/support/string_util.h>
+
+#include "src/core/lib/json/json.h"
+#include "src/core/lib/support/string.h"
+#include "src/core/lib/transport/mdstr_hash_table.h"
+
+// The main purpose of the code here is to parse the service config in
+// JSON form, which will look like this:
+//
+// {
+//   "loadBalancingPolicy": "string",  // optional
+//   "methodConfig": [  // array of one or more method_config objects
+//     {
+//       "name": [  // array of one or more name objects
+//         {
+//           "service": "string",  // required
+//           "method": "string",  // optional
+//         }
+//       ],
+//       // remaining fields are optional.
+//       // see https://developers.google.com/protocol-buffers/docs/proto3#json
+//       // for format details.
+//       "waitForReady": bool,
+//       "timeout": "duration_string",
+//       "maxRequestMessageBytes": "int64_string",
+//       "maxResponseMessageBytes": "int64_string",
+//     }
+//   ]
+// }
+
+struct grpc_service_config {
+  char* json_string;  // Underlying storage for json_tree.
+  grpc_json* json_tree;
+};
+
+grpc_service_config* grpc_service_config_create(const char* json_string) {
+  grpc_service_config* service_config = gpr_malloc(sizeof(*service_config));
+  service_config->json_string = gpr_strdup(json_string);
+  service_config->json_tree =
+      grpc_json_parse_string(service_config->json_string);
+  if (service_config->json_tree == NULL) {
+    gpr_log(GPR_INFO, "failed to parse JSON for service config");
+    gpr_free(service_config->json_string);
+    gpr_free(service_config);
+    return NULL;
+  }
+  return service_config;
+}
+
+void grpc_service_config_destroy(grpc_service_config* service_config) {
+  grpc_json_destroy(service_config->json_tree);
+  gpr_free(service_config->json_string);
+  gpr_free(service_config);
+}
+
+const char* grpc_service_config_get_lb_policy_name(
+    const grpc_service_config* service_config) {
+  const grpc_json* json = service_config->json_tree;
+  if (json->type != GRPC_JSON_OBJECT || json->key != NULL) return NULL;
+  const char* lb_policy_name = NULL;
+  for (grpc_json* field = json->child; field != NULL; field = field->next) {
+    if (field->key == NULL) return NULL;
+    if (strcmp(field->key, "loadBalancingPolicy") == 0) {
+      if (lb_policy_name != NULL) return NULL;  // Duplicate.
+      if (field->type != GRPC_JSON_STRING) return NULL;
+      lb_policy_name = field->value;
+    }
+  }
+  return lb_policy_name;
+}
+
+// Returns the number of names specified in the method config \a json.
+static size_t count_names_in_method_config_json(grpc_json* json) {
+  size_t num_names = 0;
+  for (grpc_json* field = json->child; field != NULL; field = field->next) {
+    if (field->key != NULL && strcmp(field->key, "name") == 0) ++num_names;
+  }
+  return num_names;
+}
+
+// Returns a path string for the JSON name object specified by \a json.
+// Returns NULL on error.  Caller takes ownership of result.
+static char* parse_json_method_name(grpc_json* json) {
+  if (json->type != GRPC_JSON_OBJECT) return NULL;
+  const char* service_name = NULL;
+  const char* method_name = NULL;
+  for (grpc_json* child = json->child; child != NULL; child = child->next) {
+    if (child->key == NULL) return NULL;
+    if (child->type != GRPC_JSON_STRING) return NULL;
+    if (strcmp(child->key, "service") == 0) {
+      if (service_name != NULL) return NULL;  // Duplicate.
+      if (child->value == NULL) return NULL;
+      service_name = child->value;
+    } else if (strcmp(child->key, "method") == 0) {
+      if (method_name != NULL) return NULL;  // Duplicate.
+      if (child->value == NULL) return NULL;
+      method_name = child->value;
+    }
+  }
+  if (service_name == NULL) return NULL;  // Required field.
+  char* path;
+  gpr_asprintf(&path, "/%s/%s", service_name,
+               method_name == NULL ? "*" : method_name);
+  return path;
+}
+
+// Parses the method config from \a json.  Adds an entry to \a entries for
+// each name found, incrementing \a idx for each entry added.
+// Returns false on error.
+static bool parse_json_method_config(
+    grpc_exec_ctx* exec_ctx, grpc_json* json,
+    void* (*create_value)(const grpc_json* method_config_json),
+    const grpc_mdstr_hash_table_vtable* vtable,
+    grpc_mdstr_hash_table_entry* entries, size_t* idx) {
+  // Construct value.
+  void* method_config = create_value(json);
+  if (method_config == NULL) return false;
+  // Construct list of paths.
+  bool success = false;
+  gpr_strvec paths;
+  gpr_strvec_init(&paths);
+  for (grpc_json* child = json->child; child != NULL; child = child->next) {
+    if (child->key == NULL) continue;
+    if (strcmp(child->key, "name") == 0) {
+      if (child->type != GRPC_JSON_ARRAY) goto done;
+      for (grpc_json* name = child->child; name != NULL; name = name->next) {
+        char* path = parse_json_method_name(name);
+        gpr_strvec_add(&paths, path);
+      }
+    }
+  }
+  if (paths.count == 0) goto done;  // No names specified.
+  // Add entry for each path.
+  for (size_t i = 0; i < paths.count; ++i) {
+    entries[*idx].key = grpc_mdstr_from_string(paths.strs[i]);
+    entries[*idx].value = vtable->copy_value(method_config);
+    entries[*idx].vtable = vtable;
+    ++*idx;
+  }
+  success = true;
+done:
+  vtable->destroy_value(exec_ctx, method_config);
+  gpr_strvec_destroy(&paths);
+  return success;
+}
+
+grpc_mdstr_hash_table* grpc_service_config_create_method_config_table(
+    grpc_exec_ctx* exec_ctx, const grpc_service_config* service_config,
+    void* (*create_value)(const grpc_json* method_config_json),
+    const grpc_mdstr_hash_table_vtable* vtable) {
+  const grpc_json* json = service_config->json_tree;
+  // Traverse parsed JSON tree.
+  if (json->type != GRPC_JSON_OBJECT || json->key != NULL) return NULL;
+  size_t num_entries = 0;
+  grpc_mdstr_hash_table_entry* entries = NULL;
+  for (grpc_json* field = json->child; field != NULL; field = field->next) {
+    if (field->key == NULL) return NULL;
+    if (strcmp(field->key, "methodConfig") == 0) {
+      if (entries != NULL) return NULL;  // Duplicate.
+      if (field->type != GRPC_JSON_ARRAY) return NULL;
+      // Find number of entries.
+      for (grpc_json* method = field->child; method != NULL;
+           method = method->next) {
+        num_entries += count_names_in_method_config_json(method);
+      }
+      // Populate method config table entries.
+      entries = gpr_malloc(num_entries * sizeof(grpc_mdstr_hash_table_entry));
+      size_t idx = 0;
+      for (grpc_json* method = field->child; method != NULL;
+           method = method->next) {
+        if (!parse_json_method_config(exec_ctx, method, create_value, vtable,
+                                      entries, &idx)) {
+          return NULL;
+        }
+      }
+      GPR_ASSERT(idx == num_entries);
+    }
+  }
+  // Instantiate method config table.
+  grpc_mdstr_hash_table* method_config_table = NULL;
+  if (entries != NULL) {
+    method_config_table = grpc_mdstr_hash_table_create(num_entries, entries);
+    // Clean up.
+    for (size_t i = 0; i < num_entries; ++i) {
+      GRPC_MDSTR_UNREF(exec_ctx, entries[i].key);
+      vtable->destroy_value(exec_ctx, entries[i].value);
+    }
+    gpr_free(entries);
+  }
+  return method_config_table;
+}
+
+void* grpc_method_config_table_get(grpc_exec_ctx* exec_ctx,
+                                   const grpc_mdstr_hash_table* table,
+                                   const grpc_mdstr* path) {
+  void* value = grpc_mdstr_hash_table_get(table, path);
+  // If we didn't find a match for the path, try looking for a wildcard
+  // entry (i.e., change "/service/method" to "/service/*").
+  if (value == NULL) {
+    const char* path_str = grpc_mdstr_as_c_string(path);
+    const char* sep = strrchr(path_str, '/') + 1;
+    const size_t len = (size_t)(sep - path_str);
+    char* buf = gpr_malloc(len + 2);  // '*' and NUL
+    memcpy(buf, path_str, len);
+    buf[len] = '*';
+    buf[len + 1] = '\0';
+    grpc_mdstr* wildcard_path = grpc_mdstr_from_string(buf);
+    gpr_free(buf);
+    value = grpc_mdstr_hash_table_get(table, wildcard_path);
+    GRPC_MDSTR_UNREF(exec_ctx, wildcard_path);
+  }
+  return value;
+}
diff --git a/src/core/lib/transport/service_config.h b/src/core/lib/transport/service_config.h
new file mode 100644
index 0000000000..f0897170fa
--- /dev/null
+++ b/src/core/lib/transport/service_config.h
@@ -0,0 +1,71 @@
+//
+// 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_LIB_TRANSPORT_SERVICE_CONFIG_H
+#define GRPC_CORE_LIB_TRANSPORT_SERVICE_CONFIG_H
+
+#include <grpc/impl/codegen/grpc_types.h>
+
+#include "src/core/lib/json/json.h"
+#include "src/core/lib/transport/mdstr_hash_table.h"
+
+typedef struct grpc_service_config grpc_service_config;
+
+grpc_service_config* grpc_service_config_create(const char* json_string);
+void grpc_service_config_destroy(grpc_service_config* service_config);
+
+/// Gets the LB policy name from \a service_config.
+/// Returns NULL if no LB policy name was specified.
+/// Caller does NOT take ownership.
+const char* grpc_service_config_get_lb_policy_name(
+    const grpc_service_config* service_config);
+
+/// Creates a method config table based on the data in \a json.
+/// The table's keys are request paths.  The table's value type is
+/// returned by \a create_value(), based on data parsed from the JSON tree.
+/// \a vtable provides methods used to manage the values.
+/// Returns NULL on error.
+grpc_mdstr_hash_table* grpc_service_config_create_method_config_table(
+    grpc_exec_ctx* exec_ctx, const grpc_service_config* service_config,
+    void* (*create_value)(const grpc_json* method_config_json),
+    const grpc_mdstr_hash_table_vtable* vtable);
+
+/// A helper function for looking up values in the table returned by
+/// \a grpc_service_config_create_method_config_table().
+/// Gets the method config for the specified \a path, which should be of
+/// the form "/service/method".
+/// Returns NULL if the method has no config.
+/// Caller does NOT own a reference to the result.
+void* grpc_method_config_table_get(grpc_exec_ctx* exec_ctx,
+                                   const grpc_mdstr_hash_table* table,
+                                   const grpc_mdstr* path);
+
+#endif /* GRPC_CORE_LIB_TRANSPORT_SERVICE_CONFIG_H */
diff --git a/src/cpp/client/channel_cc.cc b/src/cpp/client/channel_cc.cc
index 5f1d00d2b4..357d8317ad 100644
--- a/src/cpp/client/channel_cc.cc
+++ b/src/cpp/client/channel_cc.cc
@@ -48,6 +48,7 @@
 #include <grpc++/support/time.h>
 #include <grpc/grpc.h>
 #include <grpc/slice.h>
+#include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
 #include "src/core/lib/profiling/timers.h"
 
@@ -61,6 +62,35 @@ Channel::Channel(const grpc::string& host, grpc_channel* channel)
 
 Channel::~Channel() { grpc_channel_destroy(c_channel_); }
 
+namespace {
+
+grpc::string GetChannelInfoField(grpc_channel* channel,
+                                 grpc_channel_info* channel_info,
+                                 char*** channel_info_field) {
+  char* value = NULL;
+  memset(channel_info, 0, sizeof(*channel_info));
+  *channel_info_field = &value;
+  grpc_channel_get_info(channel, channel_info);
+  if (value == NULL) return "";
+  grpc::string result = value;
+  gpr_free(value);
+  return result;
+}
+
+}  // namespace
+
+grpc::string Channel::GetLoadBalancingPolicyName() const {
+  grpc_channel_info channel_info;
+  return GetChannelInfoField(c_channel_, &channel_info,
+                             &channel_info.lb_policy_name);
+}
+
+grpc::string Channel::GetServiceConfigJSON() const {
+  grpc_channel_info channel_info;
+  return GetChannelInfoField(c_channel_, &channel_info,
+                             &channel_info.service_config_json);
+}
+
 Call Channel::CreateCall(const RpcMethod& method, ClientContext* context,
                          CompletionQueue* cq) {
   const bool kRegistered = method.channel_tag() && context->authority().empty();
diff --git a/src/cpp/common/channel_arguments.cc b/src/cpp/common/channel_arguments.cc
index bc0b68b3e0..1fdd106130 100644
--- a/src/cpp/common/channel_arguments.cc
+++ b/src/cpp/common/channel_arguments.cc
@@ -148,6 +148,11 @@ void ChannelArguments::SetLoadBalancingPolicyName(
   SetString(GRPC_ARG_LB_POLICY_NAME, lb_policy_name);
 }
 
+void ChannelArguments::SetServiceConfigJSON(
+    const grpc::string& service_config_json) {
+  SetString(GRPC_ARG_SERVICE_CONFIG, service_config_json);
+}
+
 void ChannelArguments::SetInt(const grpc::string& key, int value) {
   grpc_arg arg;
   arg.type = GRPC_ARG_INTEGER;
diff --git a/src/python/grpcio/grpc_core_dependencies.py b/src/python/grpcio/grpc_core_dependencies.py
index 5affff10f5..bfd706a78b 100644
--- a/src/python/grpcio/grpc_core_dependencies.py
+++ b/src/python/grpcio/grpc_core_dependencies.py
@@ -181,8 +181,8 @@ CORE_SOURCE_FILES = [
   'src/core/lib/transport/mdstr_hash_table.c',
   'src/core/lib/transport/metadata.c',
   'src/core/lib/transport/metadata_batch.c',
-  'src/core/lib/transport/method_config.c',
   'src/core/lib/transport/pid_controller.c',
+  'src/core/lib/transport/service_config.c',
   'src/core/lib/transport/static_metadata.c',
   'src/core/lib/transport/timeout_encoding.c',
   'src/core/lib/transport/transport.c',
diff --git a/src/python/grpcio_tests/tests/interop/client.py b/src/python/grpcio_tests/tests/interop/client.py
index 4fbf58f7d9..afaa466254 100644
--- a/src/python/grpcio_tests/tests/interop/client.py
+++ b/src/python/grpcio_tests/tests/interop/client.py
@@ -43,11 +43,13 @@ from tests.interop import resources
 def _args():
   parser = argparse.ArgumentParser()
   parser.add_argument(
-      '--server_host', help='the host to which to connect', type=str)
+      '--server_host', help='the host to which to connect', type=str,
+      default="127.0.0.1")
   parser.add_argument(
       '--server_port', help='the port to which to connect', type=int)
   parser.add_argument(
-      '--test_case', help='the test case to execute', type=str)
+      '--test_case', help='the test case to execute', type=str,
+      default="large_unary")
   parser.add_argument(
       '--use_tls', help='require a secure connection', default=False,
       type=resources.parse_bool)
@@ -55,7 +57,7 @@ def _args():
       '--use_test_ca', help='replace platform root CAs with ca.pem',
       default=False, type=resources.parse_bool)
   parser.add_argument(
-      '--server_host_override',
+      '--server_host_override', default="foo.test.google.fr",
       help='the server host to which to claim to connect', type=str)
   parser.add_argument('--oauth_scope', help='scope for OAuth tokens', type=str)
   parser.add_argument(