src/core/ext/filters/client_channel/resolver_registry.cc

/*
 *
 * Copyright 2015 gRPC authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

#include "src/core/ext/filters/client_channel/resolver_registry.h"

#include <string.h>

#include <grpc/support/alloc.h>
#include <grpc/support/log.h>
#include <grpc/support/string_util.h>

#define MAX_RESOLVERS 10
#define DEFAULT_RESOLVER_PREFIX_MAX_LENGTH 32

static grpc_resolver_factory* g_all_of_the_resolvers[MAX_RESOLVERS];
static int g_number_of_resolvers = 0;

static char g_default_resolver_prefix[DEFAULT_RESOLVER_PREFIX_MAX_LENGTH] =
    "dns:///";

void grpc_resolver_registry_init() {}

void grpc_resolver_registry_shutdown(void) {
  for (int i = 0; i < g_number_of_resolvers; i++) {
    grpc_resolver_factory_unref(g_all_of_the_resolvers[i]);
  }
  // FIXME(ctiller): this should live in grpc_resolver_registry_init,
  // however that would have the client_channel plugin call this AFTER we start
  // registering resolvers from third party plugins, and so they'd never show
  // up.
  // We likely need some kind of dependency system for plugins.... what form
  // that takes is TBD.
  g_number_of_resolvers = 0;
}

void grpc_resolver_registry_set_default_prefix(
    const char* default_resolver_prefix) {
  const size_t len = strlen(default_resolver_prefix);
  GPR_ASSERT(len < DEFAULT_RESOLVER_PREFIX_MAX_LENGTH &&
             "default resolver prefix too long");
  GPR_ASSERT(len > 0 && "default resolver prefix can't be empty");
  // By the previous assert, default_resolver_prefix is safe to be copied with a
  // plain strcpy.
  strcpy(g_default_resolver_prefix, default_resolver_prefix);
}

void grpc_register_resolver_type(grpc_resolver_factory* factory) {
  int i;
  for (i = 0; i < g_number_of_resolvers; i++) {
    GPR_ASSERT(0 != strcmp(factory->vtable->scheme,
                           g_all_of_the_resolvers[i]->vtable->scheme));
  }
  GPR_ASSERT(g_number_of_resolvers != MAX_RESOLVERS);
  grpc_resolver_factory_ref(factory);
  g_all_of_the_resolvers[g_number_of_resolvers++] = factory;
}

static grpc_resolver_factory* lookup_factory(const char* name) {
  int i;

  for (i = 0; i < g_number_of_resolvers; i++) {
    if (0 == strcmp(name, g_all_of_the_resolvers[i]->vtable->scheme)) {
      return g_all_of_the_resolvers[i];
    }
  }
  return nullptr;
}

grpc_resolver_factory* grpc_resolver_factory_lookup(const char* name) {
  grpc_resolver_factory* f = lookup_factory(name);
  if (f) grpc_resolver_factory_ref(f);
  return f;
}

static grpc_resolver_factory* lookup_factory_by_uri(grpc_uri* uri) {
  if (!uri) return nullptr;
  return lookup_factory(uri->scheme);
}

static grpc_resolver_factory* resolve_factory(grpc_exec_ctx* exec_ctx,
                                              const char* target,
                                              grpc_uri** uri,
                                              char** canonical_target) {
  grpc_resolver_factory* factory = nullptr;

  GPR_ASSERT(uri != nullptr);
  *uri = grpc_uri_parse(exec_ctx, target, 1);
  factory = lookup_factory_by_uri(*uri);
  if (factory == nullptr) {
    grpc_uri_destroy(*uri);
    gpr_asprintf(canonical_target, "%s%s", g_default_resolver_prefix, target);
    *uri = grpc_uri_parse(exec_ctx, *canonical_target, 1);
    factory = lookup_factory_by_uri(*uri);
    if (factory == nullptr) {
      grpc_uri_destroy(grpc_uri_parse(exec_ctx, target, 0));
      grpc_uri_destroy(grpc_uri_parse(exec_ctx, *canonical_target, 0));
      gpr_log(GPR_ERROR, "don't know how to resolve '%s' or '%s'", target,
              *canonical_target);
    }
  }
  return factory;
}

grpc_resolver* grpc_resolver_create(grpc_exec_ctx* exec_ctx, const char* target,
                                    const grpc_channel_args* args,
                                    grpc_pollset_set* pollset_set,
                                    grpc_combiner* combiner) {
  grpc_uri* uri = nullptr;
  char* canonical_target = nullptr;
  grpc_resolver_factory* factory =
      resolve_factory(exec_ctx, target, &uri, &canonical_target);
  grpc_resolver* resolver;
  grpc_resolver_args resolver_args;
  memset(&resolver_args, 0, sizeof(resolver_args));
  resolver_args.uri = uri;
  resolver_args.args = args;
  resolver_args.pollset_set = pollset_set;
  resolver_args.combiner = combiner;
  resolver =
      grpc_resolver_factory_create_resolver(exec_ctx, factory, &resolver_args);
  grpc_uri_destroy(uri);
  gpr_free(canonical_target);
  return resolver;
}

char* grpc_get_default_authority(grpc_exec_ctx* exec_ctx, const char* target) {
  grpc_uri* uri = nullptr;
  char* canonical_target = nullptr;
  grpc_resolver_factory* factory =
      resolve_factory(exec_ctx, target, &uri, &canonical_target);
  char* authority = grpc_resolver_factory_get_default_authority(factory, uri);
  grpc_uri_destroy(uri);
  gpr_free(canonical_target);
  return authority;
}

char* grpc_resolver_factory_add_default_prefix_if_needed(
    grpc_exec_ctx* exec_ctx, const char* target) {
  grpc_uri* uri = nullptr;
  char* canonical_target = nullptr;
  resolve_factory(exec_ctx, target, &uri, &canonical_target);
  grpc_uri_destroy(uri);
  return canonical_target == nullptr ? gpr_strdup(target) : canonical_target;
}