Allow fetching service config via grpc_channel_get_info().

include/grpc/impl/codegen/grpc_types.h

@@ -473,6 +473,9 @@ typedef struct {
   /* If non-NULL, will be set to point to a string indicating the LB
    * policy name.  Caller takes ownership. */
   char **lb_policy_name;
+  /* If non-NULL, will be set to point to a string containing the
+   * service config used by the channel in JSON form. */
+  char **service_config_json;
 } grpc_channel_info;
 
 typedef struct grpc_resource_quota grpc_resource_quota;

src/core/ext/client_channel/client_channel.c

@@ -144,6 +144,8 @@ 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() */
@@ -250,6 +252,7 @@ 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) {
     // Find LB policy name.
@@ -305,8 +308,9 @@ static void on_resolver_result_changed(grpc_exec_ctx *exec_ctx, void *arg,
         grpc_channel_args_find(chand->resolver_result, GRPC_ARG_SERVICE_CONFIG);
     if (channel_arg != NULL) {
       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(channel_arg->value.string);
+          grpc_service_config_create(service_config_json);
       if (service_config != NULL) {
         method_params_table = grpc_service_config_create_method_config_table(
             service_config, method_parameters_create_from_json,
@@ -334,6 +338,10 @@ 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(chand->method_params_table);
   }
@@ -469,6 +477,11 @@ 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);
 }
 
@@ -512,6 +525,7 @@ 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(chand->method_params_table);
   }

test/core/client_channel/lb_policies_test.c

@@ -43,6 +43,7 @@
 
 #include "src/core/ext/client_channel/client_channel.h"
 #include "src/core/ext/client_channel/lb_policy_registry.h"
+#include "src/core/lib/channel/channel_args.h"
 #include "src/core/lib/channel/channel_stack.h"
 #include "src/core/lib/support/string.h"
 #include "src/core/lib/surface/channel.h"
@@ -642,21 +643,43 @@ static void test_pending_calls(size_t concurrent_calls) {
 }
 
 static void test_get_channel_info() {
-  grpc_channel *channel = grpc_insecure_channel_create(
-      "test:127.0.0.1:1234?lb_policy=round_robin", NULL, NULL);
+  grpc_channel *channel =
+      grpc_insecure_channel_create("ipv4:127.0.0.1:1234", NULL, NULL);
   // Ensures that resolver returns.
   grpc_channel_check_connectivity_state(channel, true /* try_to_connect */);
-  // Use grpc_channel_get_info() to get LB policy name.
-  char *lb_policy_name = NULL;
+  // First, request no fields.  This is a no-op.
   grpc_channel_info channel_info;
+  memset(&channel_info, 0, sizeof(channel_info));
+  grpc_channel_get_info(channel, &channel_info);
+  // Request LB policy name.
+  char *lb_policy_name = NULL;
   channel_info.lb_policy_name = &lb_policy_name;
   grpc_channel_get_info(channel, &channel_info);
   GPR_ASSERT(lb_policy_name != NULL);
-  GPR_ASSERT(strcmp(lb_policy_name, "round_robin") == 0);
+  GPR_ASSERT(strcmp(lb_policy_name, "pick_first") == 0);
   gpr_free(lb_policy_name);
-  // Try again without requesting anything.  This is a no-op.
-  channel_info.lb_policy_name = NULL;
+  // Request service config, which does not exist, so we'll get nothing back.
+  memset(&channel_info, 0, sizeof(channel_info));
+  char *service_config_json = "dummy_string";
+  channel_info.service_config_json = &service_config_json;
+  grpc_channel_get_info(channel, &channel_info);
+  GPR_ASSERT(service_config_json == NULL);
+  // Recreate the channel such that it has a service config.
+  grpc_channel_destroy(channel);
+  grpc_arg arg;
+  arg.type = GRPC_ARG_STRING;
+  arg.key = GRPC_ARG_SERVICE_CONFIG;
+  arg.value.string = "{\"lb_policy_name\": \"round_robin\"}";
+  grpc_channel_args *args = grpc_channel_args_copy_and_add(NULL, &arg, 1);
+  channel = grpc_insecure_channel_create("ipv4:127.0.0.1:1234", args, NULL);
+  grpc_channel_args_destroy(args);
+  // Ensures that resolver returns.
+  grpc_channel_check_connectivity_state(channel, true /* try_to_connect */);
+  // Now request the service config again.
   grpc_channel_get_info(channel, &channel_info);
+  GPR_ASSERT(service_config_json != NULL);
+  GPR_ASSERT(strcmp(service_config_json, arg.value.string) == 0);
+  gpr_free(service_config_json);
   // Clean up.
   grpc_channel_destroy(channel);
 }