Encode method config table in channel args instead of in resolver result.

12 files changed, 137 insertions, 48 deletions

diff --git a/src/core/ext/client_config/client_channel.c b/src/core/ext/client_config/client_channel.c
index 73e62fcbbf..96c8c62c04 100644
--- a/src/core/ext/client_config/client_channel.c
+++ b/src/core/ext/client_config/client_channel.c
@@ -43,6 +43,7 @@
 #include <grpc/support/useful.h>
 
 #include "src/core/ext/client_config/lb_policy_registry.h"
+#include "src/core/ext/client_config/method_config.h"
 #include "src/core/ext/client_config/subchannel.h"
 #include "src/core/lib/channel/channel_args.h"
 #include "src/core/lib/channel/connected_channel.h"
@@ -70,15 +71,14 @@ typedef struct client_channel_channel_data {
   /** client channel factory */
   grpc_client_channel_factory *client_channel_factory;
 
-  /** mutex protecting client configuration, including all
-      variables below in this data structure */
+  /** mutex protecting all variables below in this data structure */
   gpr_mu mu;
-  /** currently active load balancer - guarded by mu */
+  /** currently active load balancer */
   grpc_lb_policy *lb_policy;
-  /** incoming resolver result - set by resolver.next(), guarded by mu */
-  grpc_resolver_result *incoming_resolver_result;
-  /** current resolver result */
-  grpc_resolver_result *current_resolver_result;
+  /** method config table */
+  grpc_method_config_table *method_config_table;
+  /** incoming resolver result - set by resolver.next() */
+  grpc_resolver_result *resolver_result;
   /** a list of closures that are all waiting for config to come in */
   grpc_closure_list waiting_for_config_closures;
   /** resolver callback */
@@ -176,23 +176,23 @@ static void on_resolver_result_changed(grpc_exec_ctx *exec_ctx, void *arg,
   channel_data *chand = arg;
   grpc_lb_policy *lb_policy = NULL;
   grpc_lb_policy *old_lb_policy;
+  grpc_method_config_table *method_config_table = NULL;
   grpc_connectivity_state state = GRPC_CHANNEL_TRANSIENT_FAILURE;
   bool exit_idle = false;
   grpc_error *state_error = GRPC_ERROR_CREATE("No load balancing policy");
 
-  if (chand->incoming_resolver_result != NULL) {
+  if (chand->resolver_result != NULL) {
     grpc_lb_policy_args lb_policy_args;
     lb_policy_args.server_name =
-        grpc_resolver_result_get_server_name(chand->incoming_resolver_result);
+        grpc_resolver_result_get_server_name(chand->resolver_result);
     lb_policy_args.addresses =
-        grpc_resolver_result_get_addresses(chand->incoming_resolver_result);
-    lb_policy_args.additional_args = grpc_resolver_result_get_lb_policy_args(
-        chand->incoming_resolver_result);
+        grpc_resolver_result_get_addresses(chand->resolver_result);
+    lb_policy_args.additional_args =
+        grpc_resolver_result_get_lb_policy_args(chand->resolver_result);
     lb_policy_args.client_channel_factory = chand->client_channel_factory;
     lb_policy = grpc_lb_policy_create(
         exec_ctx,
-        grpc_resolver_result_get_lb_policy_name(
-            chand->incoming_resolver_result),
+        grpc_resolver_result_get_lb_policy_name(chand->resolver_result),
         &lb_policy_args);
     if (lb_policy != NULL) {
       GRPC_LB_POLICY_REF(lb_policy, "config_change");
@@ -200,11 +200,15 @@ 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);
     }
-    if (chand->current_resolver_result != NULL) {
-      grpc_resolver_result_unref(exec_ctx, chand->current_resolver_result);
+    const grpc_arg *channel_arg = grpc_channel_args_find(
+        lb_policy_args.additional_args, GRPC_ARG_SERVICE_CONFIG);
+    if (channel_arg != NULL) {
+      GPR_ASSERT(channel_arg->type == GRPC_ARG_POINTER);
+      method_config_table = grpc_method_config_table_ref(
+          (grpc_method_config_table *)channel_arg->value.pointer.p);
     }
-    chand->current_resolver_result = chand->incoming_resolver_result;
-    chand->incoming_resolver_result = NULL;
+    grpc_resolver_result_unref(exec_ctx, chand->resolver_result);
+    chand->resolver_result = NULL;
   }
 
   if (lb_policy != NULL) {
@@ -215,6 +219,10 @@ static void on_resolver_result_changed(grpc_exec_ctx *exec_ctx, void *arg,
   gpr_mu_lock(&chand->mu);
   old_lb_policy = chand->lb_policy;
   chand->lb_policy = lb_policy;
+  if (chand->method_config_table != NULL) {
+    grpc_method_config_table_unref(chand->method_config_table);
+  }
+  chand->method_config_table = method_config_table;
   if (lb_policy != NULL) {
     grpc_exec_ctx_enqueue_list(exec_ctx, &chand->waiting_for_config_closures,
                                NULL);
@@ -238,8 +246,7 @@ static void on_resolver_result_changed(grpc_exec_ctx *exec_ctx, void *arg,
       watch_lb_policy(exec_ctx, chand, lb_policy, state);
     }
     GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
-    grpc_resolver_next(exec_ctx, chand->resolver,
-                       &chand->incoming_resolver_result,
+    grpc_resolver_next(exec_ctx, chand->resolver, &chand->resolver_result,
                        &chand->on_resolver_result_changed);
     gpr_mu_unlock(&chand->mu);
   } else {
@@ -376,8 +383,8 @@ static void cc_destroy_channel_elem(grpc_exec_ctx *exec_ctx,
                                      chand->interested_parties);
     GRPC_LB_POLICY_UNREF(exec_ctx, chand->lb_policy, "channel");
   }
-  if (chand->current_resolver_result != NULL) {
-    grpc_resolver_result_unref(exec_ctx, chand->current_resolver_result);
+  if (chand->method_config_table != NULL) {
+    grpc_method_config_table_unref(chand->method_config_table);
   }
   grpc_connectivity_state_destroy(exec_ctx, &chand->state_tracker);
   grpc_pollset_set_destroy(chand->interested_parties);
@@ -512,11 +519,9 @@ static void subchannel_ready(grpc_exec_ctx *exec_ctx, void *arg,
     /* Get method config. */
 // FIXME: need to actually use the config data!
 // FIXME: think about refcounting vs. atomicity here
-    grpc_method_config_table* table = grpc_resolver_result_get_method_configs(
-        chand->current_resolver_result);
-    if (table != NULL) {
+    if (chand->method_config_table != NULL) {
       calld->method_config = grpc_method_config_table_get_method_config(
-          table, calld->path);
+          chand->method_config_table, calld->path);
     }
     /* Create call on subchannel. */
     grpc_subchannel_call *subchannel_call = NULL;
@@ -626,8 +631,7 @@ static bool pick_subchannel(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
   if (chand->resolver != NULL && !chand->started_resolving) {
     chand->started_resolving = true;
     GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
-    grpc_resolver_next(exec_ctx, chand->resolver,
-                       &chand->incoming_resolver_result,
+    grpc_resolver_next(exec_ctx, chand->resolver, &chand->resolver_result,
                        &chand->on_resolver_result_changed);
   }
   if (chand->resolver != NULL) {
@@ -836,7 +840,7 @@ void grpc_client_channel_finish_initialization(
       chand->exit_idle_when_lb_policy_arrives) {
     chand->started_resolving = true;
     GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
-    grpc_resolver_next(exec_ctx, resolver, &chand->incoming_resolver_result,
+    grpc_resolver_next(exec_ctx, resolver, &chand->resolver_result,
                        &chand->on_resolver_result_changed);
   }
   chand->client_channel_factory = client_channel_factory;
@@ -858,8 +862,7 @@ grpc_connectivity_state grpc_client_channel_check_connectivity_state(
       if (!chand->started_resolving && chand->resolver != NULL) {
         GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
         chand->started_resolving = true;
-        grpc_resolver_next(exec_ctx, chand->resolver,
-                           &chand->incoming_resolver_result,
+        grpc_resolver_next(exec_ctx, chand->resolver, &chand->resolver_result,
                            &chand->on_resolver_result_changed);
       }
     }
diff --git a/src/core/ext/client_config/method_config.c b/src/core/ext/client_config/method_config.c
index e3589153fb..989f776967 100644
--- a/src/core/ext/client_config/method_config.c
+++ b/src/core/ext/client_config/method_config.c
@@ -33,9 +33,11 @@
 
 #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 <grpc/support/time.h>
 
 #include "src/core/lib/transport/metadata.h"
 
@@ -212,3 +214,72 @@ grpc_method_config* grpc_method_config_table_get_method_config(
   }
   return grpc_method_config_ref(method_config);
 }
+
+static void* copy_arg(void* p) {
+  return grpc_method_config_table_ref(p);
+}
+
+static void destroy_arg(void* p) {
+  grpc_method_config_table_unref(p);
+}
+
+static int cmp_arg(void* p1, void* p2) {
+  grpc_method_config_table* t1 = p1;
+  grpc_method_config_table* t2 = p2;
+  for (size_t i = 0; i < GPR_ARRAY_SIZE(t1->entries); ++i) {
+    grpc_method_config_table_entry* e1 = &t1->entries[i];
+    grpc_method_config_table_entry* e2 = &t2->entries[i];
+    // Compare paths by hash value.
+    if (e1->path->hash < e2->path->hash) return -1;
+    if (e1->path->hash > e2->path->hash) return 1;
+    // Compare wait_for_ready.
+    const bool wait_for_ready1 =
+        e1->method_config->wait_for_ready == NULL
+        ? false : *e1->method_config->wait_for_ready;
+    const bool wait_for_ready2 =
+        e2->method_config->wait_for_ready == NULL
+        ? false : *e2->method_config->wait_for_ready;
+    if (wait_for_ready1 < wait_for_ready2) return -1;
+    if (wait_for_ready1 > wait_for_ready2) return 1;
+    // Compare timeout.
+    const gpr_timespec timeout1 =
+        e1->method_config->timeout == NULL
+        ? gpr_inf_past(GPR_CLOCK_MONOTONIC) : *e1->method_config->timeout;
+    const gpr_timespec timeout2 =
+        e2->method_config->timeout == NULL
+        ? gpr_inf_past(GPR_CLOCK_MONOTONIC) : *e2->method_config->timeout;
+    const int timeout_result = gpr_time_cmp(timeout1, timeout2);
+    if (timeout_result != 0) return timeout_result;
+    // Compare max_request_message_bytes.
+    const int32_t max_request_message_bytes1 =
+        e1->method_config->max_request_message_bytes == NULL
+        ? -1 : *e1->method_config->max_request_message_bytes;
+    const int32_t max_request_message_bytes2 =
+        e2->method_config->max_request_message_bytes == NULL
+        ? -1 : *e2->method_config->max_request_message_bytes;
+    if (max_request_message_bytes1 < max_request_message_bytes2) return -1;
+    if (max_request_message_bytes1 > max_request_message_bytes2) return 1;
+    // Compare max_response_message_bytes.
+    const int32_t max_response_message_bytes1 =
+        e1->method_config->max_response_message_bytes == NULL
+        ? -1 : *e1->method_config->max_response_message_bytes;
+    const int32_t max_response_message_bytes2 =
+        e2->method_config->max_response_message_bytes == NULL
+        ? -1 : *e2->method_config->max_response_message_bytes;
+    if (max_response_message_bytes1 < max_response_message_bytes2) return -1;
+    if (max_response_message_bytes1 > max_response_message_bytes2) return 1;
+  }
+  return 0;
+}
+
+static grpc_arg_pointer_vtable arg_vtable = {copy_arg, destroy_arg, cmp_arg};
+
+grpc_arg grpc_method_config_table_create_channel_arg(
+    grpc_method_config_table* table) {
+  grpc_arg arg;
+  arg.type = GRPC_ARG_POINTER;
+  arg.key = GRPC_ARG_SERVICE_CONFIG;
+  arg.value.pointer.p = grpc_method_config_table_ref(table);
+  arg.value.pointer.vtable = &arg_vtable;
+  return arg;
+}
diff --git a/src/core/ext/client_config/method_config.h b/src/core/ext/client_config/method_config.h
index 9490e296b2..2be0cd1006 100644
--- a/src/core/ext/client_config/method_config.h
+++ b/src/core/ext/client_config/method_config.h
@@ -35,6 +35,7 @@
 #include <stdbool.h>
 
 #include <grpc/impl/codegen/gpr_types.h>
+#include <grpc/impl/codegen/grpc_types.h>
 
 #include "src/core/lib/transport/metadata.h"
 
@@ -82,4 +83,8 @@ void grpc_method_config_table_add_method_config(
 grpc_method_config* grpc_method_config_table_get_method_config(
     grpc_method_config_table* table, grpc_mdstr* path);
 
+/// Returns a channel arg containing \a table.
+grpc_arg grpc_method_config_table_create_channel_arg(
+    grpc_method_config_table* table);
+
 #endif /* GRPC_CORE_EXT_CLIENT_CONFIG_METHOD_CONFIG_H */
diff --git a/src/core/ext/client_config/resolver_result.c b/src/core/ext/client_config/resolver_result.c
index 5c5ffb2635..16d124d205 100644
--- a/src/core/ext/client_config/resolver_result.c
+++ b/src/core/ext/client_config/resolver_result.c
@@ -49,13 +49,11 @@ struct grpc_resolver_result {
   grpc_lb_addresses* addresses;
   char* lb_policy_name;
   grpc_channel_args* lb_policy_args;
-  grpc_method_config_table* method_configs;
 };
 
 grpc_resolver_result* grpc_resolver_result_create(
     const char* server_name, grpc_lb_addresses* addresses,
-    const char* lb_policy_name, grpc_channel_args* lb_policy_args,
-    grpc_method_config_table* method_configs) {
+    const char* lb_policy_name, grpc_channel_args* lb_policy_args) {
   grpc_resolver_result* result = gpr_malloc(sizeof(*result));
   memset(result, 0, sizeof(*result));
   gpr_ref_init(&result->refs, 1);
@@ -63,7 +61,6 @@ grpc_resolver_result* grpc_resolver_result_create(
   result->addresses = addresses;
   result->lb_policy_name = gpr_strdup(lb_policy_name);
   result->lb_policy_args = lb_policy_args;
-  result->method_configs = grpc_method_config_table_ref(method_configs);
   return result;
 }
 
@@ -78,7 +75,6 @@ void grpc_resolver_result_unref(grpc_exec_ctx* exec_ctx,
     grpc_lb_addresses_destroy(result->addresses, NULL /* user_data_destroy */);
     gpr_free(result->lb_policy_name);
     grpc_channel_args_destroy(result->lb_policy_args);
-    grpc_method_config_table_unref(result->method_configs);
     gpr_free(result);
   }
 }
@@ -101,8 +97,3 @@ grpc_channel_args* grpc_resolver_result_get_lb_policy_args(
     grpc_resolver_result* result) {
   return result->lb_policy_args;
 }
-
-grpc_method_config_table* grpc_resolver_result_get_method_configs(
-    grpc_resolver_result* result) {
-  return result->method_configs;
-}
diff --git a/src/core/ext/client_config/resolver_result.h b/src/core/ext/client_config/resolver_result.h
index e6127f1d6d..707c8c2cf5 100644
--- a/src/core/ext/client_config/resolver_result.h
+++ b/src/core/ext/client_config/resolver_result.h
@@ -33,7 +33,6 @@
 #define GRPC_CORE_EXT_CLIENT_CONFIG_RESOLVER_RESULT_H
 
 #include "src/core/ext/client_config/lb_policy_factory.h"
-#include "src/core/ext/client_config/method_config.h"
 #include "src/core/lib/iomgr/resolve_address.h"
 
 // TODO(roth, ctiller): In the long term, we are considering replacing
@@ -52,8 +51,7 @@ typedef struct grpc_resolver_result grpc_resolver_result;
 /// Takes ownership of \a addresses, \a lb_policy_args.
 grpc_resolver_result* grpc_resolver_result_create(
     const char* server_name, grpc_lb_addresses* addresses,
-    const char* lb_policy_name, grpc_channel_args* lb_policy_args,
-    grpc_method_config_table* method_configs);
+    const char* lb_policy_name, grpc_channel_args* lb_policy_args);
 
 void grpc_resolver_result_ref(grpc_resolver_result* result);
 void grpc_resolver_result_unref(grpc_exec_ctx* exec_ctx,
@@ -67,7 +65,5 @@ const char* grpc_resolver_result_get_lb_policy_name(
     grpc_resolver_result* result);
 grpc_channel_args* grpc_resolver_result_get_lb_policy_args(
     grpc_resolver_result* result);
-grpc_method_config_table* grpc_resolver_result_get_method_configs(
-    grpc_resolver_result* result);
 
 #endif /* GRPC_CORE_EXT_CLIENT_CONFIG_RESOLVER_RESULT_H */
diff --git a/src/core/ext/lb_policy/grpclb/grpclb.c b/src/core/ext/lb_policy/grpclb/grpclb.c
index 8105c4415d..de3438be81 100644
--- a/src/core/ext/lb_policy/grpclb/grpclb.c
+++ b/src/core/ext/lb_policy/grpclb/grpclb.c
@@ -112,6 +112,7 @@
 #include "src/core/ext/client_config/parse_address.h"
 #include "src/core/ext/lb_policy/grpclb/grpclb.h"
 #include "src/core/ext/lb_policy/grpclb/load_balancer_api.h"
+#include "src/core/lib/channel/channel_args.h"
 #include "src/core/lib/iomgr/sockaddr.h"
 #include "src/core/lib/iomgr/sockaddr_utils.h"
 #include "src/core/lib/support/string.h"
@@ -285,6 +286,7 @@ typedef struct glb_lb_policy {
 
   const char *server_name;
   grpc_client_channel_factory *cc_factory;
+  grpc_channel_args *args;
 
   /** for communicating with the LB server */
   grpc_channel *lb_channel;
@@ -442,6 +444,7 @@ static grpc_lb_policy *create_rr(grpc_exec_ctx *exec_ctx,
   args.server_name = glb_policy->server_name;
   args.client_channel_factory = glb_policy->cc_factory;
   args.addresses = process_serverlist(serverlist);
+  args.additional_args = glb_policy->args;
 
   grpc_lb_policy *rr = grpc_lb_policy_create(exec_ctx, "round_robin", &args);
 
@@ -567,6 +570,7 @@ static grpc_lb_policy *glb_create(grpc_exec_ctx *exec_ctx,
    * Create a client channel over them to communicate with a LB service */
   glb_policy->server_name = gpr_strdup(args->server_name);
   glb_policy->cc_factory = args->client_channel_factory;
+  glb_policy->args = grpc_channel_args_copy(args->additional_args);
   GPR_ASSERT(glb_policy->cc_factory != NULL);
 
   /* construct a target from the addresses in args, given in the form
@@ -633,6 +637,7 @@ static void glb_destroy(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
   GPR_ASSERT(glb_policy->pending_picks == NULL);
   GPR_ASSERT(glb_policy->pending_pings == NULL);
   gpr_free((void *)glb_policy->server_name);
+  grpc_channel_args_destroy(glb_policy->args);
   grpc_channel_destroy(glb_policy->lb_channel);
   glb_policy->lb_channel = NULL;
   grpc_connectivity_state_destroy(exec_ctx, &glb_policy->state_tracker);
diff --git a/src/core/ext/lb_policy/pick_first/pick_first.c b/src/core/ext/lb_policy/pick_first/pick_first.c
index 466a0fdede..10030ef18b 100644
--- a/src/core/ext/lb_policy/pick_first/pick_first.c
+++ b/src/core/ext/lb_policy/pick_first/pick_first.c
@@ -470,6 +470,7 @@ static grpc_lb_policy *create_pick_first(grpc_exec_ctx *exec_ctx,
     sc_args.addr =
         (struct sockaddr *)(&args->addresses->addresses[i].address.addr);
     sc_args.addr_len = args->addresses->addresses[i].address.len;
+    sc_args.args = args->additional_args;
 
     grpc_subchannel *subchannel = grpc_client_channel_factory_create_subchannel(
         exec_ctx, args->client_channel_factory, &sc_args);
diff --git a/src/core/ext/lb_policy/round_robin/round_robin.c b/src/core/ext/lb_policy/round_robin/round_robin.c
index 037f180a9e..b6cfe8994d 100644
--- a/src/core/ext/lb_policy/round_robin/round_robin.c
+++ b/src/core/ext/lb_policy/round_robin/round_robin.c
@@ -633,6 +633,7 @@ static grpc_lb_policy *round_robin_create(grpc_exec_ctx *exec_ctx,
     sc_args.addr =
         (struct sockaddr *)(&args->addresses->addresses[i].address.addr);
     sc_args.addr_len = args->addresses->addresses[i].address.len;
+    sc_args.args = args->additional_args;
 
     grpc_subchannel *subchannel = grpc_client_channel_factory_create_subchannel(
         exec_ctx, args->client_channel_factory, &sc_args);
diff --git a/src/core/ext/resolver/dns/native/dns_resolver.c b/src/core/ext/resolver/dns/native/dns_resolver.c
index 879e26f7d9..e8ac1b12ae 100644
--- a/src/core/ext/resolver/dns/native/dns_resolver.c
+++ b/src/core/ext/resolver/dns/native/dns_resolver.c
@@ -181,7 +181,7 @@ static void dns_on_resolved(grpc_exec_ctx *exec_ctx, void *arg,
     }
     grpc_resolved_addresses_destroy(r->addresses);
     result = grpc_resolver_result_create(r->target_name, addresses,
-                                         r->lb_policy_name, NULL, NULL);
+                                         r->lb_policy_name, NULL);
   } else {
     gpr_timespec now = gpr_now(GPR_CLOCK_MONOTONIC);
     gpr_timespec next_try = gpr_backoff_step(&r->backoff_state, now);
diff --git a/src/core/ext/resolver/sockaddr/sockaddr_resolver.c b/src/core/ext/resolver/sockaddr/sockaddr_resolver.c
index 61be1b3c25..74d2015e5c 100644
--- a/src/core/ext/resolver/sockaddr/sockaddr_resolver.c
+++ b/src/core/ext/resolver/sockaddr/sockaddr_resolver.c
@@ -122,7 +122,7 @@ static void sockaddr_maybe_finish_next_locked(grpc_exec_ctx *exec_ctx,
     r->published = true;
     *r->target_result = grpc_resolver_result_create(
         "", grpc_lb_addresses_copy(r->addresses, NULL /* user_data_copy */),
-        r->lb_policy_name, NULL, NULL);
+        r->lb_policy_name, NULL);
     grpc_exec_ctx_sched(exec_ctx, r->next_completion, GRPC_ERROR_NONE, NULL);
     r->next_completion = NULL;
   }
diff --git a/src/core/lib/channel/channel_args.c b/src/core/lib/channel/channel_args.c
index 3a56b1ff20..bab6fcd9fa 100644
--- a/src/core/lib/channel/channel_args.c
+++ b/src/core/lib/channel/channel_args.c
@@ -272,6 +272,16 @@ int grpc_channel_args_compare(const grpc_channel_args *a,
   return 0;
 }
 
+const grpc_arg *grpc_channel_args_find(const grpc_channel_args *args,
+                                       const char *name) {
+  if (args != NULL) {
+    for (size_t i = 0; i < args->num_args; ++i) {
+      if (args->args[i].key == name) return &args->args[i];
+    }
+  }
+  return NULL;
+}
+
 int grpc_channel_arg_get_integer(grpc_arg *arg, grpc_integer_options options) {
   if (arg->type != GRPC_ARG_INTEGER) {
     gpr_log(GPR_ERROR, "%s ignored: it must be an integer", arg->key);
diff --git a/src/core/lib/channel/channel_args.h b/src/core/lib/channel/channel_args.h
index 586a296d1f..38fb4c55d4 100644
--- a/src/core/lib/channel/channel_args.h
+++ b/src/core/lib/channel/channel_args.h
@@ -89,6 +89,12 @@ uint32_t grpc_channel_args_compression_algorithm_get_states(
 int grpc_channel_args_compare(const grpc_channel_args *a,
                               const grpc_channel_args *b);
 
+/** Returns the value of argument \a name from \a args, or NULL if not found.
+    Note: \a name is matched using pointer equality, so it must be the
+    same instance of the string used to create the grpc_arg key. */
+const grpc_arg *grpc_channel_args_find(const grpc_channel_args *args,
+                                       const char *name);
+
 typedef struct grpc_integer_options {
   int default_value;  // Return this if value is outside of expected bounds.
   int min_value;