/** * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved. * SPDX-License-Identifier: Apache-2.0. */ #include #include #include #include #include #include #include #include #include #include #include #include #include const uint64_t NS_PER_SEC = 1000000000; const size_t AWS_DEFAULT_DNS_TTL = 30; int aws_host_address_copy(const struct aws_host_address *from, struct aws_host_address *to) { to->allocator = from->allocator; to->address = aws_string_new_from_string(to->allocator, from->address); to->host = aws_string_new_from_string(to->allocator, from->host); to->record_type = from->record_type; to->use_count = from->use_count; to->connection_failure_count = from->connection_failure_count; to->expiry = from->expiry; to->weight = from->weight; return AWS_OP_SUCCESS; } void aws_host_address_move(struct aws_host_address *from, struct aws_host_address *to) { to->allocator = from->allocator; to->address = from->address; to->host = from->host; to->record_type = from->record_type; to->use_count = from->use_count; to->connection_failure_count = from->connection_failure_count; to->expiry = from->expiry; to->weight = from->weight; AWS_ZERO_STRUCT(*from); } void aws_host_address_clean_up(struct aws_host_address *address) { if (address->address) { aws_string_destroy((void *)address->address); } if (address->host) { aws_string_destroy((void *)address->host); } AWS_ZERO_STRUCT(*address); } int aws_host_resolver_resolve_host( struct aws_host_resolver *resolver, const struct aws_string *host_name, aws_on_host_resolved_result_fn *res, const struct aws_host_resolution_config *config, void *user_data) { AWS_ASSERT(resolver->vtable && resolver->vtable->resolve_host); return resolver->vtable->resolve_host(resolver, host_name, res, config, user_data); } int aws_host_resolver_purge_cache(struct aws_host_resolver *resolver) { AWS_ASSERT(resolver->vtable && resolver->vtable->purge_cache); return resolver->vtable->purge_cache(resolver); } int aws_host_resolver_purge_cache_with_callback( struct aws_host_resolver *resolver, aws_simple_completion_callback *on_purge_cache_complete_callback, void *user_data) { AWS_PRECONDITION(resolver); AWS_PRECONDITION(resolver->vtable); if (!resolver->vtable->purge_cache_with_callback) { AWS_LOGF_ERROR(AWS_LS_IO_DNS, "purge_cache_with_callback function is not supported"); return aws_raise_error(AWS_ERROR_UNSUPPORTED_OPERATION); } return resolver->vtable->purge_cache_with_callback(resolver, on_purge_cache_complete_callback, user_data); } int aws_host_resolver_purge_host_cache( struct aws_host_resolver *resolver, const struct aws_host_resolver_purge_host_options *options) { AWS_PRECONDITION(resolver); AWS_PRECONDITION(resolver->vtable); if (!resolver->vtable->purge_host_cache) { AWS_LOGF_ERROR(AWS_LS_IO_DNS, "purge_host_cache function is not supported"); return aws_raise_error(AWS_ERROR_UNSUPPORTED_OPERATION); } return resolver->vtable->purge_host_cache(resolver, options); } int aws_host_resolver_record_connection_failure( struct aws_host_resolver *resolver, const struct aws_host_address *address) { AWS_ASSERT(resolver->vtable && resolver->vtable->record_connection_failure); return resolver->vtable->record_connection_failure(resolver, address); } /* * Used by both the resolver for its lifetime state as well as individual host entries for theirs. */ enum default_resolver_state { DRS_ACTIVE, DRS_SHUTTING_DOWN, }; struct default_host_resolver { struct aws_allocator *allocator; /* * Mutually exclusion for the whole resolver, includes all member data and all host_entry_table operations. Once * an entry is retrieved, this lock MAY be dropped but certain logic may hold both the resolver and the entry lock. * The two locks must be taken in that order. */ struct aws_mutex resolver_lock; /* host_name (aws_string*) -> host_entry* */ struct aws_hash_table host_entry_table; /* Hash table of listener entries per host name. We keep this decoupled from the host entry table to allow for * listeners to be added/removed regardless of whether or not a corresponding host entry exists. * * Any time the listener list in the listener entry becomes empty, we remove the entry from the table. This * includes when a resolver thread moves all of the available listeners to its local list. */ /* host_name (aws_string*) -> host_listener_entry* */ struct aws_hash_table listener_entry_table; enum default_resolver_state state; /* * Tracks the number of launched resolution threads that have not yet invoked their shutdown completion * callback. */ uint32_t pending_host_entry_shutdown_completion_callbacks; /* * Function to use to query current time. Overridable in construction options. */ aws_io_clock_fn *system_clock_fn; struct aws_event_loop_group *event_loop_group; }; struct host_entry { /* immutable post-creation */ struct aws_allocator *allocator; struct aws_host_resolver *resolver; struct aws_thread resolver_thread; const struct aws_string *host_name; int64_t resolve_frequency_ns; struct aws_host_resolution_config resolution_config; /* synchronized data and its lock */ struct aws_mutex entry_lock; struct aws_condition_variable entry_signal; struct aws_cache *aaaa_records; struct aws_cache *a_records; struct aws_cache *failed_connection_aaaa_records; struct aws_cache *failed_connection_a_records; struct aws_linked_list pending_resolution_callbacks; uint32_t resolves_since_last_request; uint64_t last_resolve_request_timestamp_ns; enum default_resolver_state state; struct aws_array_list new_addresses; struct aws_array_list expired_addresses; aws_simple_completion_callback *on_host_purge_complete; void *on_host_purge_complete_user_data; }; /* * A host entry's caches hold things of this type. By using this and not the host_address directly, our * on_remove callbacks for the cache have access to the host_entry. We wouldn't need to do this if those * callbacks supported user data injection, but they don't and too many internal code bases already depend * on the public API. */ struct aws_host_address_cache_entry { struct aws_host_address address; struct host_entry *entry; }; int aws_host_address_cache_entry_copy( const struct aws_host_address_cache_entry *from, struct aws_host_address_cache_entry *to) { if (aws_host_address_copy(&from->address, &to->address)) { return AWS_OP_ERR; } to->entry = from->entry; return AWS_OP_SUCCESS; } static void s_shutdown_host_entry(struct host_entry *entry) { aws_mutex_lock(&entry->entry_lock); entry->state = DRS_SHUTTING_DOWN; /* * intentionally signal under the lock; we can't guarantee the resolver * is still around once the lock is released. */ aws_condition_variable_notify_all(&entry->entry_signal); aws_mutex_unlock(&entry->entry_lock); } struct host_purge_callback_options { struct aws_allocator *allocator; struct aws_ref_count ref_count; aws_simple_completion_callback *on_purge_cache_complete_callback; void *user_data; }; static void s_host_purge_callback_options_destroy(void *user_data) { struct host_purge_callback_options *options = user_data; options->on_purge_cache_complete_callback(options->user_data); aws_mem_release(options->allocator, options); } static struct host_purge_callback_options *s_host_purge_callback_options_new( struct aws_allocator *allocator, aws_simple_completion_callback *on_purge_cache_complete_callback, void *user_data) { struct host_purge_callback_options *purge_callback_options = aws_mem_calloc(allocator, 1, sizeof(struct host_purge_callback_options)); purge_callback_options->allocator = allocator; aws_ref_count_init( &purge_callback_options->ref_count, purge_callback_options, s_host_purge_callback_options_destroy); purge_callback_options->on_purge_cache_complete_callback = on_purge_cache_complete_callback; purge_callback_options->user_data = user_data; return purge_callback_options; } static void s_purge_cache_callback(void *user_data) { struct host_purge_callback_options *purge_callback_options = user_data; aws_ref_count_release(&purge_callback_options->ref_count); } /* * resolver lock must be held before calling this function */ static void s_clear_default_resolver_entry_table_synced(struct default_host_resolver *resolver) { struct aws_hash_table *table = &resolver->host_entry_table; for (struct aws_hash_iter iter = aws_hash_iter_begin(table); !aws_hash_iter_done(&iter); aws_hash_iter_next(&iter)) { struct host_entry *entry = iter.element.value; s_shutdown_host_entry(entry); } aws_hash_table_clear(table); } static int s_resolver_purge_cache(struct aws_host_resolver *resolver) { struct default_host_resolver *default_host_resolver = resolver->impl; aws_mutex_lock(&default_host_resolver->resolver_lock); s_clear_default_resolver_entry_table_synced(default_host_resolver); aws_mutex_unlock(&default_host_resolver->resolver_lock); return AWS_OP_SUCCESS; } static void s_purge_host_cache_callback_task(struct aws_task *task, void *arg, enum aws_task_status status) { (void)status; struct host_purge_callback_options *options = arg; aws_mem_release(options->allocator, task); aws_ref_count_release(&options->ref_count); } static void s_sechdule_purge_cache_callback_async( struct default_host_resolver *default_host_resolver, struct host_purge_callback_options *purge_callback_options) { struct aws_task *task = aws_mem_calloc(default_host_resolver->allocator, 1, sizeof(struct aws_task)); aws_task_init(task, s_purge_host_cache_callback_task, purge_callback_options, "async_purge_host_callback_task"); struct aws_event_loop *loop = aws_event_loop_group_get_next_loop(default_host_resolver->event_loop_group); AWS_FATAL_ASSERT(loop != NULL); aws_event_loop_schedule_task_now(loop, task); } static int s_resolver_purge_cache_with_callback( struct aws_host_resolver *resolver, aws_simple_completion_callback *on_purge_cache_complete_callback, void *user_data) { if (!on_purge_cache_complete_callback) { return s_resolver_purge_cache(resolver); } struct default_host_resolver *default_host_resolver = resolver->impl; aws_mutex_lock(&default_host_resolver->resolver_lock); struct aws_hash_table *table = &default_host_resolver->host_entry_table; struct host_purge_callback_options *purge_callback_options = s_host_purge_callback_options_new( default_host_resolver->allocator, on_purge_cache_complete_callback, user_data); /* purge all cache */ for (struct aws_hash_iter iter = aws_hash_iter_begin(table); !aws_hash_iter_done(&iter); aws_hash_iter_next(&iter)) { struct host_entry *entry = iter.element.value; /* acquire a refernce to wait for the callback to trigger */ aws_ref_count_acquire(&purge_callback_options->ref_count); aws_mutex_lock(&entry->entry_lock); entry->on_host_purge_complete = s_purge_cache_callback; entry->on_host_purge_complete_user_data = purge_callback_options; entry->state = DRS_SHUTTING_DOWN; aws_mutex_unlock(&entry->entry_lock); } aws_hash_table_clear(table); aws_mutex_unlock(&default_host_resolver->resolver_lock); /* release the original reference async */ s_sechdule_purge_cache_callback_async(default_host_resolver, purge_callback_options); return AWS_OP_SUCCESS; } static void s_cleanup_default_resolver(struct aws_host_resolver *resolver) { struct default_host_resolver *default_host_resolver = resolver->impl; aws_event_loop_group_release(default_host_resolver->event_loop_group); aws_hash_table_clean_up(&default_host_resolver->host_entry_table); aws_hash_table_clean_up(&default_host_resolver->listener_entry_table); aws_mutex_clean_up(&default_host_resolver->resolver_lock); aws_simple_completion_callback *shutdown_callback = resolver->shutdown_options.shutdown_callback_fn; void *shutdown_completion_user_data = resolver->shutdown_options.shutdown_callback_user_data; aws_mem_release(resolver->allocator, resolver); /* invoke shutdown completion finally */ if (shutdown_callback != NULL) { shutdown_callback(shutdown_completion_user_data); } } static void resolver_destroy(struct aws_host_resolver *resolver) { struct default_host_resolver *default_host_resolver = resolver->impl; bool cleanup_resolver = false; aws_mutex_lock(&default_host_resolver->resolver_lock); AWS_FATAL_ASSERT(default_host_resolver->state == DRS_ACTIVE); s_clear_default_resolver_entry_table_synced(default_host_resolver); default_host_resolver->state = DRS_SHUTTING_DOWN; if (default_host_resolver->pending_host_entry_shutdown_completion_callbacks == 0) { cleanup_resolver = true; } aws_mutex_unlock(&default_host_resolver->resolver_lock); if (cleanup_resolver) { s_cleanup_default_resolver(resolver); } } struct pending_callback { aws_on_host_resolved_result_fn *callback; void *user_data; struct aws_linked_list_node node; }; static void s_clear_address_list(struct aws_array_list *address_list) { for (size_t i = 0; i < aws_array_list_length(address_list); ++i) { struct aws_host_address *address = NULL; aws_array_list_get_at_ptr(address_list, (void **)&address, i); aws_host_address_clean_up(address); } aws_array_list_clear(address_list); } static void s_clean_up_host_entry(struct host_entry *entry) { if (entry == NULL) { return; } /* * This can happen if the resolver's final reference drops while an unanswered query is pending on an entry. * * You could add an assertion that the resolver is in the shut down state if this condition hits but that * requires additional locking just to make the assert. */ if (!aws_linked_list_empty(&entry->pending_resolution_callbacks)) { aws_raise_error(AWS_IO_DNS_HOST_REMOVED_FROM_CACHE); } while (!aws_linked_list_empty(&entry->pending_resolution_callbacks)) { struct aws_linked_list_node *resolution_callback_node = aws_linked_list_pop_front(&entry->pending_resolution_callbacks); struct pending_callback *pending_callback = AWS_CONTAINER_OF(resolution_callback_node, struct pending_callback, node); pending_callback->callback( entry->resolver, entry->host_name, AWS_IO_DNS_HOST_REMOVED_FROM_CACHE, NULL, pending_callback->user_data); aws_mem_release(entry->allocator, pending_callback); } aws_cache_destroy(entry->aaaa_records); aws_cache_destroy(entry->a_records); aws_cache_destroy(entry->failed_connection_a_records); aws_cache_destroy(entry->failed_connection_aaaa_records); aws_string_destroy((void *)entry->host_name); s_clear_address_list(&entry->new_addresses); aws_array_list_clean_up(&entry->new_addresses); s_clear_address_list(&entry->expired_addresses); aws_array_list_clean_up(&entry->expired_addresses); aws_mem_release(entry->allocator, entry); } static void s_on_host_entry_shutdown_completion(void *user_data) { struct host_entry *entry = user_data; struct aws_host_resolver *resolver = entry->resolver; struct default_host_resolver *default_host_resolver = resolver->impl; s_clean_up_host_entry(entry); bool cleanup_resolver = false; aws_mutex_lock(&default_host_resolver->resolver_lock); --default_host_resolver->pending_host_entry_shutdown_completion_callbacks; if (default_host_resolver->state == DRS_SHUTTING_DOWN && default_host_resolver->pending_host_entry_shutdown_completion_callbacks == 0) { cleanup_resolver = true; } aws_mutex_unlock(&default_host_resolver->resolver_lock); if (cleanup_resolver) { s_cleanup_default_resolver(resolver); } } static int s_copy_address_into_array_list(struct aws_host_address *address, struct aws_array_list *address_list) { /* * This is the worst. * * We have to copy the cache address while we still have a write lock. Otherwise, connection failures * can sneak in and destroy our address by moving the address to/from the various lru caches. * * But there's no nice copy construction into an array list, so we get to * (1) Push a zeroed dummy element onto the array list * (2) Get its pointer * (3) Call aws_host_address_copy onto it. If that fails, pop the dummy element. */ struct aws_host_address dummy; AWS_ZERO_STRUCT(dummy); if (aws_array_list_push_back(address_list, &dummy)) { return AWS_OP_ERR; } struct aws_host_address *dest_copy = NULL; aws_array_list_get_at_ptr(address_list, (void **)&dest_copy, aws_array_list_length(address_list) - 1); AWS_FATAL_ASSERT(dest_copy != NULL); if (aws_host_address_copy(address, dest_copy)) { aws_array_list_pop_back(address_list); return AWS_OP_ERR; } return AWS_OP_SUCCESS; } static uint64_t s_get_system_time_for_default_resolver(struct aws_host_resolver *resolver) { struct default_host_resolver *default_resolver = resolver->impl; uint64_t timestamp = 0; (*default_resolver->system_clock_fn)(×tamp); return timestamp; } /* this only ever gets called after resolution has already run. We expect that the entry's lock has been acquired for writing before this function is called and released afterwards. */ static inline void process_records( struct host_entry *host_entry, struct aws_cache *records, struct aws_cache *failed_records) { struct aws_host_resolver *resolver = host_entry->resolver; uint64_t timestamp = s_get_system_time_for_default_resolver(resolver); size_t record_count = aws_cache_get_element_count(records); size_t expired_records = 0; /* since this only ever gets called after resolution has already run, we're in a dns outage * if everything is expired. Leave an element so we can keep trying. */ for (size_t index = 0; index < record_count && expired_records < record_count - 1; ++index) { struct aws_host_address_cache_entry *lru_element_entry = aws_lru_cache_use_lru_element(records); if (lru_element_entry->address.expiry < timestamp) { AWS_LOGF_DEBUG( AWS_LS_IO_DNS, "static: purging expired record %s for %s", lru_element_entry->address.address->bytes, lru_element_entry->address.host->bytes); expired_records++; aws_cache_remove(records, lru_element_entry->address.address); } } record_count = aws_cache_get_element_count(records); AWS_LOGF_TRACE(AWS_LS_IO_DNS, "static: remaining record count for host %d", (int)record_count); /* if we don't have any known good addresses, take the least recently used, but not expired address with a history * of spotty behavior and upgrade it for reuse. If it's expired, leave it and let the resolve fail. Better to fail * than accidentally give a kids' app an IP address to somebody's adult website when the IP address gets rebound to * a different endpoint. The moral of the story here is to not disable SSL verification! */ if (!record_count) { size_t failed_count = aws_cache_get_element_count(failed_records); for (size_t index = 0; index < failed_count; ++index) { struct aws_host_address_cache_entry *lru_element_entry = aws_lru_cache_use_lru_element(failed_records); if (timestamp >= lru_element_entry->address.expiry) { continue; } struct aws_host_address_cache_entry *to_add = aws_mem_calloc(host_entry->allocator, 1, sizeof(struct aws_host_address_cache_entry)); if (to_add == NULL) { continue; } if (aws_host_address_cache_entry_copy(lru_element_entry, to_add) || aws_cache_put(records, to_add->address.address, to_add)) { aws_host_address_clean_up(&to_add->address); aws_mem_release(host_entry->allocator, to_add); continue; } /* * Promoting an address from failed to good should trigger the new address callback */ s_copy_address_into_array_list(&lru_element_entry->address, &host_entry->new_addresses); AWS_LOGF_INFO( AWS_LS_IO_DNS, "static: promoting spotty record %s for %s back to good list", lru_element_entry->address.address->bytes, lru_element_entry->address.host->bytes); aws_cache_remove(failed_records, lru_element_entry->address.address); /* we only want to promote one per process run.*/ break; } } } static int s_resolver_purge_host_cache( struct aws_host_resolver *resolver, const struct aws_host_resolver_purge_host_options *options) { AWS_PRECONDITION(resolver); if (options == NULL) { AWS_LOGF_ERROR(AWS_LS_IO_DNS, "Cannot purge host cache; options structure is NULL."); return aws_raise_error(AWS_ERROR_INVALID_ARGUMENT); } struct default_host_resolver *default_host_resolver = resolver->impl; AWS_LOGF_INFO(AWS_LS_IO_DNS, "id=%p: purging record for %s", (void *)resolver, options->host->bytes); aws_mutex_lock(&default_host_resolver->resolver_lock); struct aws_hash_element *element = NULL; aws_hash_table_find(&default_host_resolver->host_entry_table, options->host, &element); /* Success if entry doesn't exist in cache. */ if (element == NULL) { aws_mutex_unlock(&default_host_resolver->resolver_lock); if (options->on_host_purge_complete_callback != NULL) { /* Schedule completion callback asynchronouly */ struct host_purge_callback_options *purge_callback_options = s_host_purge_callback_options_new( default_host_resolver->allocator, options->on_host_purge_complete_callback, options->user_data); s_sechdule_purge_cache_callback_async(default_host_resolver, purge_callback_options); } return AWS_OP_SUCCESS; } struct host_entry *host_entry = element->value; AWS_FATAL_ASSERT(host_entry); /* Setup the on_host_purge_complete callback. */ aws_mutex_lock(&host_entry->entry_lock); AWS_FATAL_ASSERT(!host_entry->on_host_purge_complete); AWS_FATAL_ASSERT(!host_entry->on_host_purge_complete_user_data); host_entry->on_host_purge_complete = options->on_host_purge_complete_callback; host_entry->on_host_purge_complete_user_data = options->user_data; aws_mutex_unlock(&host_entry->entry_lock); s_shutdown_host_entry(host_entry); aws_hash_table_remove_element(&default_host_resolver->host_entry_table, element); aws_mutex_unlock(&default_host_resolver->resolver_lock); return AWS_OP_SUCCESS; } static int resolver_record_connection_failure( struct aws_host_resolver *resolver, const struct aws_host_address *address) { struct default_host_resolver *default_host_resolver = resolver->impl; AWS_LOGF_INFO( AWS_LS_IO_DNS, "id=%p: recording failure for record %s for %s, moving to bad list", (void *)resolver, address->address->bytes, address->host->bytes); aws_mutex_lock(&default_host_resolver->resolver_lock); struct aws_hash_element *element = NULL; if (aws_hash_table_find(&default_host_resolver->host_entry_table, address->host, &element)) { aws_mutex_unlock(&default_host_resolver->resolver_lock); return AWS_OP_ERR; } struct host_entry *host_entry = NULL; if (element != NULL) { host_entry = element->value; AWS_FATAL_ASSERT(host_entry); } if (host_entry) { struct aws_host_address_cache_entry *cached_address_entry = NULL; aws_mutex_lock(&host_entry->entry_lock); aws_mutex_unlock(&default_host_resolver->resolver_lock); struct aws_cache *address_table = address->record_type == AWS_ADDRESS_RECORD_TYPE_AAAA ? host_entry->aaaa_records : host_entry->a_records; struct aws_cache *failed_table = address->record_type == AWS_ADDRESS_RECORD_TYPE_AAAA ? host_entry->failed_connection_aaaa_records : host_entry->failed_connection_a_records; aws_cache_find(address_table, address->address, (void **)&cached_address_entry); struct aws_host_address_cache_entry *address_entry_copy = NULL; if (cached_address_entry) { address_entry_copy = aws_mem_calloc(resolver->allocator, 1, sizeof(struct aws_host_address_cache_entry)); if (!address_entry_copy || aws_host_address_cache_entry_copy(cached_address_entry, address_entry_copy)) { goto error_host_entry_cleanup; } /* * This will trigger an expiration callback since the good caches add the removed address to the * host_entry's expired list, via the cache's on_delete callback */ if (aws_cache_remove(address_table, cached_address_entry->address.address)) { goto error_host_entry_cleanup; } address_entry_copy->address.connection_failure_count += 1; if (aws_cache_put(failed_table, address_entry_copy->address.address, address_entry_copy)) { goto error_host_entry_cleanup; } } else { if (aws_cache_find(failed_table, address->address, (void **)&cached_address_entry)) { goto error_host_entry_cleanup; } if (cached_address_entry) { cached_address_entry->address.connection_failure_count += 1; } } aws_mutex_unlock(&host_entry->entry_lock); return AWS_OP_SUCCESS; error_host_entry_cleanup: if (address_entry_copy) { aws_host_address_clean_up(&address_entry_copy->address); aws_mem_release(resolver->allocator, address_entry_copy); } aws_mutex_unlock(&host_entry->entry_lock); return AWS_OP_ERR; } aws_mutex_unlock(&default_host_resolver->resolver_lock); return AWS_OP_SUCCESS; } /* * A bunch of convenience functions for the host resolver background thread function */ static struct aws_host_address_cache_entry *s_find_cached_address_entry_aux( struct aws_cache *primary_records, struct aws_cache *fallback_records, const struct aws_string *address) { struct aws_host_address_cache_entry *found = NULL; aws_cache_find(primary_records, address, (void **)&found); if (found == NULL) { aws_cache_find(fallback_records, address, (void **)&found); } return found; } /* * Looks in both the good and failed connection record sets for a given host record */ static struct aws_host_address_cache_entry *s_find_cached_address_entry( struct host_entry *entry, const struct aws_string *address, enum aws_address_record_type record_type) { switch (record_type) { case AWS_ADDRESS_RECORD_TYPE_AAAA: return s_find_cached_address_entry_aux(entry->aaaa_records, entry->failed_connection_aaaa_records, address); case AWS_ADDRESS_RECORD_TYPE_A: return s_find_cached_address_entry_aux(entry->a_records, entry->failed_connection_a_records, address); default: return NULL; } } static struct aws_host_address_cache_entry *s_get_lru_address_entry_aux( struct aws_cache *primary_records, struct aws_cache *fallback_records) { struct aws_host_address_cache_entry *address_entry = aws_lru_cache_use_lru_element(primary_records); if (address_entry == NULL) { aws_lru_cache_use_lru_element(fallback_records); } return address_entry; } /* * Looks in both the good and failed connection record sets for the LRU host record */ static struct aws_host_address_cache_entry *s_get_lru_address( struct host_entry *entry, enum aws_address_record_type record_type) { switch (record_type) { case AWS_ADDRESS_RECORD_TYPE_AAAA: return s_get_lru_address_entry_aux(entry->aaaa_records, entry->failed_connection_aaaa_records); case AWS_ADDRESS_RECORD_TYPE_A: return s_get_lru_address_entry_aux(entry->a_records, entry->failed_connection_a_records); default: return NULL; } } static void s_update_address_cache( struct host_entry *host_entry, struct aws_array_list *address_list, uint64_t new_expiration) { AWS_PRECONDITION(host_entry); AWS_PRECONDITION(address_list); for (size_t i = 0; i < aws_array_list_length(address_list); ++i) { struct aws_host_address *fresh_resolved_address = NULL; aws_array_list_get_at_ptr(address_list, (void **)&fresh_resolved_address, i); struct aws_host_address_cache_entry *address_to_cache_entry = s_find_cached_address_entry( host_entry, fresh_resolved_address->address, fresh_resolved_address->record_type); if (address_to_cache_entry) { address_to_cache_entry->address.expiry = new_expiration; AWS_LOGF_TRACE( AWS_LS_IO_DNS, "static: updating expiry for %s for host %s to %llu", address_to_cache_entry->address.address->bytes, host_entry->host_name->bytes, (unsigned long long)new_expiration); } else { address_to_cache_entry = aws_mem_calloc(host_entry->allocator, 1, sizeof(struct aws_host_address_cache_entry)); aws_host_address_move(fresh_resolved_address, &address_to_cache_entry->address); address_to_cache_entry->address.expiry = new_expiration; address_to_cache_entry->entry = host_entry; struct aws_cache *address_table = address_to_cache_entry->address.record_type == AWS_ADDRESS_RECORD_TYPE_AAAA ? host_entry->aaaa_records : host_entry->a_records; if (aws_cache_put(address_table, address_to_cache_entry->address.address, address_to_cache_entry)) { AWS_LOGF_ERROR( AWS_LS_IO_DNS, "static: could not add new address to host entry cache for host '%s' in " "s_update_address_cache.", host_entry->host_name->bytes); continue; } AWS_LOGF_DEBUG( AWS_LS_IO_DNS, "static: new address resolved %s for host %s caching", address_to_cache_entry->address.address->bytes, host_entry->host_name->bytes); struct aws_host_address new_address_copy; if (aws_host_address_copy(&address_to_cache_entry->address, &new_address_copy)) { AWS_LOGF_ERROR( AWS_LS_IO_DNS, "static: could not copy address for new-address list for host '%s' in s_update_address_cache.", host_entry->host_name->bytes); continue; } if (aws_array_list_push_back(&host_entry->new_addresses, &new_address_copy)) { aws_host_address_clean_up(&new_address_copy); AWS_LOGF_ERROR( AWS_LS_IO_DNS, "static: could not push address to new-address list for host '%s' in s_update_address_cache.", host_entry->host_name->bytes); continue; } } } } static void s_copy_address_into_callback_set( struct aws_host_address_cache_entry *entry, struct aws_array_list *callback_addresses, const struct aws_string *host_name) { if (entry != NULL) { if (s_copy_address_into_array_list(&entry->address, callback_addresses)) { AWS_LOGF_ERROR( AWS_LS_IO_DNS, "static: failed to vend address %s for host %s to caller", entry->address.address->bytes, host_name->bytes); return; } entry->address.use_count += 1; AWS_LOGF_TRACE( AWS_LS_IO_DNS, "static: vending address %s for host %s to caller", entry->address.address->bytes, host_name->bytes); } } static bool s_host_entry_finished_pred(void *user_data) { struct host_entry *entry = user_data; return entry->state == DRS_SHUTTING_DOWN; } static bool s_host_entry_finished_or_pending_request_pred(void *user_data) { struct host_entry *entry = user_data; return entry->state == DRS_SHUTTING_DOWN || !aws_linked_list_empty(&entry->pending_resolution_callbacks); } static const uint64_t AWS_MINIMUM_WAIT_BETWEEN_DNS_QUERIES_NS = 100000000; /* 100 ms */ static void aws_host_resolver_thread(void *arg) { struct host_entry *host_entry = arg; uint64_t max_no_solicitation_interval = aws_timestamp_convert( aws_max_u64(1, host_entry->resolution_config.max_ttl), AWS_TIMESTAMP_SECS, AWS_TIMESTAMP_NANOS, NULL); uint64_t wait_between_resolves_interval = aws_min_u64(max_no_solicitation_interval, host_entry->resolve_frequency_ns); uint64_t shutdown_only_wait_time = AWS_MINIMUM_WAIT_BETWEEN_DNS_QUERIES_NS; uint64_t request_interruptible_wait_time = 0; if (wait_between_resolves_interval > shutdown_only_wait_time) { request_interruptible_wait_time = wait_between_resolves_interval - shutdown_only_wait_time; } struct aws_linked_list listener_list; aws_linked_list_init(&listener_list); struct aws_linked_list listener_destroy_list; aws_linked_list_init(&listener_destroy_list); bool keep_going = true; struct aws_array_list address_list; AWS_ZERO_STRUCT(address_list); struct aws_array_list new_address_list; AWS_ZERO_STRUCT(new_address_list); struct aws_array_list expired_address_list; AWS_ZERO_STRUCT(expired_address_list); if (aws_array_list_init_dynamic(&address_list, host_entry->allocator, 4, sizeof(struct aws_host_address))) { goto done; } if (aws_array_list_init_dynamic(&new_address_list, host_entry->allocator, 4, sizeof(struct aws_host_address))) { goto done; } if (aws_array_list_init_dynamic(&expired_address_list, host_entry->allocator, 4, sizeof(struct aws_host_address))) { goto done; } while (keep_going) { /* resolve and then process each record */ int err_code = AWS_ERROR_SUCCESS; if (host_entry->resolution_config.impl( host_entry->allocator, host_entry->host_name, &address_list, host_entry->resolution_config.impl_data)) { err_code = aws_last_error(); } if (err_code == AWS_ERROR_SUCCESS) { AWS_LOGF_DEBUG( AWS_LS_IO_DNS, "static, resolving host %s successful, returned %d addresses", aws_string_c_str(host_entry->host_name), (int)aws_array_list_length(&address_list)); } else { AWS_LOGF_WARN( AWS_LS_IO_DNS, "static, resolving host %s failed, ec %d (%s)", aws_string_c_str(host_entry->host_name), err_code, aws_error_debug_str(err_code)); } uint64_t timestamp = s_get_system_time_for_default_resolver(host_entry->resolver); uint64_t new_expiry = timestamp + (host_entry->resolution_config.max_ttl * NS_PER_SEC); struct aws_linked_list pending_resolve_copy; aws_linked_list_init(&pending_resolve_copy); /* * Within the lock we * (1) Update the cache with the newly resolved addresses * (2) Process all held addresses looking for expired or promotable ones * (3) Prep for callback invocations */ aws_mutex_lock(&host_entry->entry_lock); if (!err_code) { s_update_address_cache(host_entry, &address_list, new_expiry); } /* * process and clean_up records in the entry. occasionally, failed connect records will be upgraded * for retry. */ process_records(host_entry, host_entry->aaaa_records, host_entry->failed_connection_aaaa_records); process_records(host_entry, host_entry->a_records, host_entry->failed_connection_a_records); aws_linked_list_swap_contents(&pending_resolve_copy, &host_entry->pending_resolution_callbacks); aws_mutex_unlock(&host_entry->entry_lock); /* * Clean up resolved addressed outside of the lock */ s_clear_address_list(&address_list); struct aws_host_address address_array[2]; AWS_ZERO_ARRAY(address_array); /* * Perform the actual subscriber notifications */ while (!aws_linked_list_empty(&pending_resolve_copy)) { struct aws_linked_list_node *resolution_callback_node = aws_linked_list_pop_front(&pending_resolve_copy); struct pending_callback *pending_callback = AWS_CONTAINER_OF(resolution_callback_node, struct pending_callback, node); struct aws_array_list callback_address_list; aws_array_list_init_static(&callback_address_list, address_array, 2, sizeof(struct aws_host_address)); aws_mutex_lock(&host_entry->entry_lock); s_copy_address_into_callback_set( s_get_lru_address(host_entry, AWS_ADDRESS_RECORD_TYPE_AAAA), &callback_address_list, host_entry->host_name); s_copy_address_into_callback_set( s_get_lru_address(host_entry, AWS_ADDRESS_RECORD_TYPE_A), &callback_address_list, host_entry->host_name); aws_mutex_unlock(&host_entry->entry_lock); size_t callback_address_list_size = aws_array_list_length(&callback_address_list); if (callback_address_list_size > 0) { AWS_LOGF_DEBUG( AWS_LS_IO_DNS, "static, invoking resolution callback for host %s with %d addresses", aws_string_c_str(host_entry->host_name), (int)callback_address_list_size); } else { AWS_LOGF_DEBUG( AWS_LS_IO_DNS, "static, invoking resolution callback for host %s with failure", aws_string_c_str(host_entry->host_name)); } if (callback_address_list_size > 0) { pending_callback->callback( host_entry->resolver, host_entry->host_name, AWS_OP_SUCCESS, &callback_address_list, pending_callback->user_data); } else { int error_code = (err_code != AWS_ERROR_SUCCESS) ? err_code : AWS_IO_DNS_QUERY_FAILED; pending_callback->callback( host_entry->resolver, host_entry->host_name, error_code, NULL, pending_callback->user_data); } s_clear_address_list(&callback_address_list); aws_mem_release(host_entry->allocator, pending_callback); } aws_mutex_lock(&host_entry->entry_lock); ++host_entry->resolves_since_last_request; /* * A long resolve frequency matched with a connection failure can induce a state of DNS starvation, where * additional resolution requests go into the queue but since there's no good records and the thread is sleeping * for a long time, nothing happens. * * While we could make the wait predicate also check the queue of requests, there is a worry that a * host that can't be resolved (user error, dns record removal, etc...) could lead to a "spammy" scenario * where the thread generates DNS requests extremely quickly, ie, the sleep becomes almost instant. * * We'd like to be able to express the wait here as something a bit more complex: * * "Wait until either (1) shutdown notice, or (2) a small amount of time has passed and there are pending * requests, or (3) the resolution interval has passed" * * While seemingly complicated, we can do this actually just by chaining two waits: * * (1) The first wait is for a short amount of time and only predicates on the shutdown notice * (2) The second wait is for the remaining frequency interval and predicates on either the shutdown notice * or a pending resolve request * * This leaves us with wait behavior where: * (1) Shutdown always fully interrupts and immediately causes the thread function to complete * (2) Absent shutdown, there is always a controllable, non-trivial sleep between resolves * (3) Starvation is avoided as pending requests can wake the resolver thread independent of resolution * frequency */ aws_condition_variable_wait_for_pred( &host_entry->entry_signal, &host_entry->entry_lock, shutdown_only_wait_time, s_host_entry_finished_pred, host_entry); if (request_interruptible_wait_time > 0) { aws_condition_variable_wait_for_pred( &host_entry->entry_signal, &host_entry->entry_lock, request_interruptible_wait_time, s_host_entry_finished_or_pending_request_pred, host_entry); } aws_mutex_unlock(&host_entry->entry_lock); /* * This is a bit awkward that we unlock the entry and then relock both the resolver and the entry, but it * is mandatory that -- in order to maintain the consistent view of the resolver table (entry exist => entry * is alive and can be queried) -- we have the resolver lock as well before making the decision to remove * the entry from the table and terminate the thread. */ struct default_host_resolver *resolver = host_entry->resolver->impl; aws_mutex_lock(&resolver->resolver_lock); aws_mutex_lock(&host_entry->entry_lock); uint64_t now = s_get_system_time_for_default_resolver(host_entry->resolver); /* * The only way we terminate the loop with pending queries is if the resolver itself has no more references * to it and is going away. In that case, the pending queries will be completed (with failure) by the * final clean up of this entry. */ if (aws_linked_list_empty(&host_entry->pending_resolution_callbacks) && host_entry->last_resolve_request_timestamp_ns + max_no_solicitation_interval < now) { host_entry->state = DRS_SHUTTING_DOWN; } keep_going = host_entry->state == DRS_ACTIVE; if (!keep_going) { aws_hash_table_remove(&resolver->host_entry_table, host_entry->host_name, NULL, NULL); } aws_array_list_swap_contents(&host_entry->new_addresses, &new_address_list); aws_array_list_swap_contents(&host_entry->expired_addresses, &expired_address_list); aws_mutex_unlock(&host_entry->entry_lock); aws_mutex_unlock(&resolver->resolver_lock); s_clear_address_list(&new_address_list); s_clear_address_list(&expired_address_list); } AWS_LOGF_DEBUG( AWS_LS_IO_DNS, "static: Either no requests have been made for an address for %s for the duration " "of the ttl, or this thread is being forcibly shutdown. Killing thread.", host_entry->host_name->bytes); done: AWS_FATAL_ASSERT(aws_array_list_length(&address_list) == 0); AWS_FATAL_ASSERT(aws_array_list_length(&new_address_list) == 0); AWS_FATAL_ASSERT(aws_array_list_length(&expired_address_list) == 0); aws_array_list_clean_up(&address_list); aws_array_list_clean_up(&new_address_list); aws_array_list_clean_up(&expired_address_list); /* trigger the purge complete callback */ if (host_entry->on_host_purge_complete != NULL) { host_entry->on_host_purge_complete(host_entry->on_host_purge_complete_user_data); } /* please don't fail */ aws_thread_current_at_exit(s_on_host_entry_shutdown_completion, host_entry); } static void on_cache_entry_removed_helper(struct aws_host_address_cache_entry *entry) { AWS_LOGF_DEBUG( AWS_LS_IO_DNS, "static: purging address %s for host %s from " "the cache due to cache eviction or shutdown", entry->address.address->bytes, entry->address.host->bytes); struct aws_allocator *allocator = entry->address.allocator; aws_host_address_clean_up(&entry->address); aws_mem_release(allocator, entry); } static void on_good_address_entry_removed(void *value) { struct aws_host_address_cache_entry *entry = value; if (entry == NULL) { return; } s_copy_address_into_array_list(&entry->address, &entry->entry->expired_addresses); on_cache_entry_removed_helper(entry); } static void on_failed_address_entry_removed(void *value) { struct aws_host_address_cache_entry *entry = value; on_cache_entry_removed_helper(entry); } /* * The resolver lock must be held before calling this function */ static inline int create_and_init_host_entry( struct aws_host_resolver *resolver, const struct aws_string *host_name, aws_on_host_resolved_result_fn *res, const struct aws_host_resolution_config *config, uint64_t timestamp, void *user_data) { struct host_entry *new_host_entry = aws_mem_calloc(resolver->allocator, 1, sizeof(struct host_entry)); if (!new_host_entry) { return AWS_OP_ERR; } new_host_entry->resolver = resolver; new_host_entry->allocator = resolver->allocator; new_host_entry->last_resolve_request_timestamp_ns = timestamp; new_host_entry->resolves_since_last_request = 0; new_host_entry->resolve_frequency_ns = (config->resolve_frequency_ns != 0) ? config->resolve_frequency_ns : NS_PER_SEC; new_host_entry->state = DRS_ACTIVE; bool thread_init = false; struct pending_callback *pending_callback = NULL; const struct aws_string *host_string_copy = aws_string_new_from_string(resolver->allocator, host_name); if (AWS_UNLIKELY(!host_string_copy)) { goto setup_host_entry_error; } new_host_entry->host_name = host_string_copy; new_host_entry->a_records = aws_cache_new_lru( new_host_entry->allocator, aws_hash_string, aws_hash_callback_string_eq, NULL, on_good_address_entry_removed, config->max_ttl); if (AWS_UNLIKELY(!new_host_entry->a_records)) { goto setup_host_entry_error; } new_host_entry->aaaa_records = aws_cache_new_lru( new_host_entry->allocator, aws_hash_string, aws_hash_callback_string_eq, NULL, on_good_address_entry_removed, config->max_ttl); if (AWS_UNLIKELY(!new_host_entry->aaaa_records)) { goto setup_host_entry_error; } new_host_entry->failed_connection_a_records = aws_cache_new_lru( new_host_entry->allocator, aws_hash_string, aws_hash_callback_string_eq, NULL, on_failed_address_entry_removed, config->max_ttl); if (AWS_UNLIKELY(!new_host_entry->failed_connection_a_records)) { goto setup_host_entry_error; } new_host_entry->failed_connection_aaaa_records = aws_cache_new_lru( new_host_entry->allocator, aws_hash_string, aws_hash_callback_string_eq, NULL, on_failed_address_entry_removed, config->max_ttl); if (AWS_UNLIKELY(!new_host_entry->failed_connection_aaaa_records)) { goto setup_host_entry_error; } if (aws_array_list_init_dynamic( &new_host_entry->new_addresses, new_host_entry->allocator, 4, sizeof(struct aws_host_address))) { goto setup_host_entry_error; } if (aws_array_list_init_dynamic( &new_host_entry->expired_addresses, new_host_entry->allocator, 4, sizeof(struct aws_host_address))) { goto setup_host_entry_error; } aws_linked_list_init(&new_host_entry->pending_resolution_callbacks); pending_callback = aws_mem_acquire(resolver->allocator, sizeof(struct pending_callback)); if (AWS_UNLIKELY(!pending_callback)) { goto setup_host_entry_error; } /*add the current callback here */ pending_callback->user_data = user_data; pending_callback->callback = res; aws_linked_list_push_back(&new_host_entry->pending_resolution_callbacks, &pending_callback->node); aws_mutex_init(&new_host_entry->entry_lock); new_host_entry->resolution_config = *config; aws_condition_variable_init(&new_host_entry->entry_signal); aws_thread_init(&new_host_entry->resolver_thread, resolver->allocator); thread_init = true; struct default_host_resolver *default_host_resolver = resolver->impl; if (AWS_UNLIKELY( aws_hash_table_put(&default_host_resolver->host_entry_table, host_string_copy, new_host_entry, NULL))) { goto setup_host_entry_error; } struct aws_thread_options thread_options = *aws_default_thread_options(); thread_options.join_strategy = AWS_TJS_MANAGED; thread_options.name = aws_byte_cursor_from_c_str("AwsHostResolver"); /* 15 characters is max for Linux */ if (aws_thread_launch( &new_host_entry->resolver_thread, aws_host_resolver_thread, new_host_entry, &thread_options)) { goto setup_host_entry_error; } ++default_host_resolver->pending_host_entry_shutdown_completion_callbacks; return AWS_OP_SUCCESS; setup_host_entry_error: if (thread_init) { aws_thread_clean_up(&new_host_entry->resolver_thread); } // If we registered a callback, clear it. So that we don’t trigger callback and return an error. if (!aws_linked_list_empty(&new_host_entry->pending_resolution_callbacks)) { aws_linked_list_remove(&pending_callback->node); } s_clean_up_host_entry(new_host_entry); return AWS_OP_ERR; } static int default_resolve_host( struct aws_host_resolver *resolver, const struct aws_string *host_name, aws_on_host_resolved_result_fn *res, const struct aws_host_resolution_config *config, void *user_data) { int result = AWS_OP_SUCCESS; AWS_LOGF_DEBUG(AWS_LS_IO_DNS, "id=%p: Host resolution requested for %s", (void *)resolver, host_name->bytes); uint64_t timestamp = s_get_system_time_for_default_resolver(resolver); struct default_host_resolver *default_host_resolver = resolver->impl; aws_mutex_lock(&default_host_resolver->resolver_lock); struct aws_hash_element *element = NULL; /* we don't care about the error code here, only that the host_entry was found or not. */ aws_hash_table_find(&default_host_resolver->host_entry_table, host_name, &element); struct host_entry *host_entry = NULL; if (element != NULL) { host_entry = element->value; AWS_FATAL_ASSERT(host_entry != NULL); } if (!host_entry) { AWS_LOGF_DEBUG( AWS_LS_IO_DNS, "id=%p: No cached entries found for %s starting new resolver thread.", (void *)resolver, host_name->bytes); result = create_and_init_host_entry(resolver, host_name, res, config, timestamp, user_data); aws_mutex_unlock(&default_host_resolver->resolver_lock); return result; } aws_mutex_lock(&host_entry->entry_lock); /* * We don't need to make any resolver side-affects in the remaining logic and it's impossible for the entry * to disappear underneath us while holding its lock, so its safe to release the resolver lock and let other * things query other entries. */ aws_mutex_unlock(&default_host_resolver->resolver_lock); host_entry->last_resolve_request_timestamp_ns = timestamp; host_entry->resolves_since_last_request = 0; struct aws_host_address_cache_entry *aaaa_entry = aws_lru_cache_use_lru_element(host_entry->aaaa_records); struct aws_host_address *aaaa_record = (aaaa_entry != NULL) ? &aaaa_entry->address : NULL; struct aws_host_address_cache_entry *a_entry = aws_lru_cache_use_lru_element(host_entry->a_records); struct aws_host_address *a_record = (a_entry != NULL) ? &a_entry->address : NULL; struct aws_host_address address_array[2]; AWS_ZERO_ARRAY(address_array); struct aws_array_list callback_address_list; aws_array_list_init_static(&callback_address_list, address_array, 2, sizeof(struct aws_host_address)); if ((aaaa_record || a_record)) { AWS_LOGF_DEBUG( AWS_LS_IO_DNS, "id=%p: cached entries found for %s returning to caller.", (void *)resolver, host_name->bytes); /* these will all need to be copied so that we don't hold the lock during the callback. */ if (aaaa_record) { struct aws_host_address aaaa_record_cpy; aws_host_address_copy(aaaa_record, &aaaa_record_cpy); aws_array_list_push_back(&callback_address_list, &aaaa_record_cpy); AWS_LOGF_TRACE( AWS_LS_IO_DNS, "id=%p: vending address %s for host %s to caller", (void *)resolver, aaaa_record->address->bytes, host_entry->host_name->bytes); } if (a_record) { struct aws_host_address a_record_cpy; aws_host_address_copy(a_record, &a_record_cpy); aws_array_list_push_back(&callback_address_list, &a_record_cpy); AWS_LOGF_TRACE( AWS_LS_IO_DNS, "id=%p: vending address %s for host %s to caller", (void *)resolver, a_record->address->bytes, host_entry->host_name->bytes); } aws_mutex_unlock(&host_entry->entry_lock); /* we don't want to do the callback WHILE we hold the lock someone may reentrantly call us. */ // TODO: Fire the callback asynchronously res(resolver, host_name, AWS_OP_SUCCESS, &callback_address_list, user_data); for (size_t i = 0; i < aws_array_list_length(&callback_address_list); ++i) { struct aws_host_address *address_ptr = NULL; aws_array_list_get_at_ptr(&callback_address_list, (void **)&address_ptr, i); aws_host_address_clean_up(address_ptr); } aws_array_list_clean_up(&callback_address_list); return result; } struct pending_callback *pending_callback = aws_mem_acquire(default_host_resolver->allocator, sizeof(struct pending_callback)); if (pending_callback != NULL) { pending_callback->user_data = user_data; pending_callback->callback = res; aws_linked_list_push_back(&host_entry->pending_resolution_callbacks, &pending_callback->node); /* * intentionally signal under the lock; similar to the shutdown case, we can't guarantee the resolver * is still around once the lock is released. */ aws_condition_variable_notify_all(&host_entry->entry_signal); } else { result = AWS_OP_ERR; } aws_mutex_unlock(&host_entry->entry_lock); return result; } static size_t default_get_host_address_count( struct aws_host_resolver *host_resolver, const struct aws_string *host_name, uint32_t flags) { struct default_host_resolver *default_host_resolver = host_resolver->impl; size_t address_count = 0; aws_mutex_lock(&default_host_resolver->resolver_lock); struct aws_hash_element *element = NULL; aws_hash_table_find(&default_host_resolver->host_entry_table, host_name, &element); if (element != NULL) { struct host_entry *host_entry = element->value; if (host_entry != NULL) { aws_mutex_lock(&host_entry->entry_lock); if ((flags & AWS_GET_HOST_ADDRESS_COUNT_RECORD_TYPE_A) != 0) { address_count += aws_cache_get_element_count(host_entry->a_records); } if ((flags & AWS_GET_HOST_ADDRESS_COUNT_RECORD_TYPE_AAAA) != 0) { address_count += aws_cache_get_element_count(host_entry->aaaa_records); } aws_mutex_unlock(&host_entry->entry_lock); } } aws_mutex_unlock(&default_host_resolver->resolver_lock); return address_count; } static struct aws_host_resolver_vtable s_vtable = { .purge_cache = s_resolver_purge_cache, .purge_cache_with_callback = s_resolver_purge_cache_with_callback, .resolve_host = default_resolve_host, .record_connection_failure = resolver_record_connection_failure, .get_host_address_count = default_get_host_address_count, .destroy = resolver_destroy, .purge_host_cache = s_resolver_purge_host_cache, }; static void s_aws_host_resolver_destroy(struct aws_host_resolver *resolver) { AWS_ASSERT(resolver->vtable && resolver->vtable->destroy); resolver->vtable->destroy(resolver); } struct aws_host_resolver *aws_host_resolver_new_default( struct aws_allocator *allocator, const struct aws_host_resolver_default_options *options) { AWS_FATAL_ASSERT(options != NULL); AWS_ASSERT(options->el_group); struct aws_host_resolver *resolver = NULL; struct default_host_resolver *default_host_resolver = NULL; if (!aws_mem_acquire_many( allocator, 2, &resolver, sizeof(struct aws_host_resolver), &default_host_resolver, sizeof(struct default_host_resolver))) { return NULL; } AWS_ZERO_STRUCT(*resolver); AWS_ZERO_STRUCT(*default_host_resolver); AWS_LOGF_INFO( AWS_LS_IO_DNS, "id=%p: Initializing default host resolver with %llu max host entries.", (void *)resolver, (unsigned long long)options->max_entries); resolver->vtable = &s_vtable; resolver->allocator = allocator; resolver->impl = default_host_resolver; default_host_resolver->event_loop_group = aws_event_loop_group_acquire(options->el_group); default_host_resolver->allocator = allocator; default_host_resolver->pending_host_entry_shutdown_completion_callbacks = 0; default_host_resolver->state = DRS_ACTIVE; aws_mutex_init(&default_host_resolver->resolver_lock); if (aws_hash_table_init( &default_host_resolver->host_entry_table, allocator, options->max_entries, aws_hash_string, aws_hash_callback_string_eq, NULL, NULL)) { goto on_error; } aws_ref_count_init(&resolver->ref_count, resolver, (aws_simple_completion_callback *)s_aws_host_resolver_destroy); if (options->shutdown_options != NULL) { resolver->shutdown_options = *options->shutdown_options; } if (options->system_clock_override_fn != NULL) { default_host_resolver->system_clock_fn = options->system_clock_override_fn; } else { default_host_resolver->system_clock_fn = aws_high_res_clock_get_ticks; } return resolver; on_error: s_cleanup_default_resolver(resolver); return NULL; } struct aws_host_resolver *aws_host_resolver_acquire(struct aws_host_resolver *resolver) { if (resolver != NULL) { aws_ref_count_acquire(&resolver->ref_count); } return resolver; } void aws_host_resolver_release(struct aws_host_resolver *resolver) { if (resolver != NULL) { aws_ref_count_release(&resolver->ref_count); } } size_t aws_host_resolver_get_host_address_count( struct aws_host_resolver *resolver, const struct aws_string *host_name, uint32_t flags) { return resolver->vtable->get_host_address_count(resolver, host_name, flags); } struct aws_host_resolution_config aws_host_resolver_init_default_resolution_config(void) { struct aws_host_resolution_config config = { .impl = aws_default_dns_resolve, .max_ttl = AWS_DEFAULT_DNS_TTL, .impl_data = NULL, .resolve_frequency_ns = NS_PER_SEC, }; return config; }