text: /*
   *
   * 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/ext/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 NULL;
  }
  
  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 NULL;
    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 = NULL;
  
    GPR_ASSERT(uri != NULL);
    *uri = grpc_uri_parse(exec_ctx, target, 1);
    factory = lookup_factory_by_uri(*uri);
    if (factory == NULL) {
      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 == NULL) {
        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 = NULL;
    char *canonical_target = NULL;
    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 = NULL;
    char *canonical_target = NULL;
    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 = NULL;
    char *canonical_target = NULL;
    resolve_factory(exec_ctx, target, &uri, &canonical_target);
    grpc_uri_destroy(uri);
    return canonical_target == NULL ? gpr_strdup(target) : canonical_target;
  }
  