Disable SRV and TXT lookups for localhost

src/core/ext/filters/client_channel/resolver/dns/c_ares/dns_resolver_ares.cc

@@ -465,11 +465,16 @@ static grpc_error* blocking_resolve_address_ares(
 static grpc_address_resolver_vtable ares_resolver = {
     grpc_resolve_address_ares, blocking_resolve_address_ares};
 
+static bool should_use_ares(const char* resolver_env) {
+  return resolver_env != nullptr && gpr_stricmp(resolver_env, "ares") == 0;
+}
+
 void grpc_resolver_dns_ares_init() {
   char* resolver_env = gpr_getenv("GRPC_DNS_RESOLVER");
   /* TODO(zyc): Turn on c-ares based resolver by default after the address
      sorter and the CNAME support are added. */
-  if (resolver_env != nullptr && gpr_stricmp(resolver_env, "ares") == 0) {
+  if (should_use_ares(resolver_env)) {
+    gpr_log(GPR_DEBUG, "Using ares dns resolver");
     address_sorting_init();
     grpc_error* error = grpc_ares_init();
     if (error != GRPC_ERROR_NONE) {
@@ -489,7 +494,7 @@ void grpc_resolver_dns_ares_init() {
 
 void grpc_resolver_dns_ares_shutdown() {
   char* resolver_env = gpr_getenv("GRPC_DNS_RESOLVER");
-  if (resolver_env != nullptr && gpr_stricmp(resolver_env, "ares") == 0) {
+  if (should_use_ares(resolver_env)) {
     address_sorting_shutdown();
     grpc_ares_cleanup();
   }

src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.cc

@@ -510,6 +510,28 @@ static bool resolve_as_ip_literal_locked(
   return out;
 }
 
+static bool target_matches_localhost_inner(const char* name, char** host,
+                                           char** port) {
+  if (!gpr_split_host_port(name, host, port)) {
+    gpr_log(GPR_INFO, "Unable to split host and port for name: %s", name);
+    return false;
+  }
+  if (gpr_stricmp(*host, "localhost") == 0) {
+    return true;
+  } else {
+    return false;
+  }
+}
+
+static bool target_matches_localhost(const char* name) {
+  char* host = nullptr;
+  char* port = nullptr;
+  bool out = target_matches_localhost_inner(name, &host, &port);
+  gpr_free(host);
+  gpr_free(port);
+  return out;
+}
+
 static grpc_ares_request* grpc_dns_lookup_ares_locked_impl(
     const char* dns_server, const char* name, const char* default_port,
     grpc_pollset_set* interested_parties, grpc_closure* on_done,
@@ -536,6 +558,13 @@ static grpc_ares_request* grpc_dns_lookup_ares_locked_impl(
     GRPC_CLOSURE_SCHED(on_done, GRPC_ERROR_NONE);
     return r;
   }
+  // Don't query for SRV and TXT records if the target is "localhost", so
+  // as to cut down on lookups over the network, especially in tests:
+  // https://github.com/grpc/proposal/pull/79
+  if (target_matches_localhost(name)) {
+    check_grpclb = false;
+    r->service_config_json_out = nullptr;
+  }
   // Look up name using c-ares lib.
   grpc_dns_lookup_ares_continue_after_check_localhost_and_ip_literals_locked(
       r, dns_server, name, default_port, interested_parties, check_grpclb,

test/core/client_channel/resolvers/dns_resolver_connectivity_test.cc

@@ -76,7 +76,10 @@ static grpc_ares_request* my_dns_lookup_ares_locked(
   } else {
     gpr_mu_unlock(&g_mu);
     *addresses = grpc_core::MakeUnique<grpc_core::ServerAddressList>();
-    (*addresses)->emplace_back(nullptr, 0, nullptr);
+    grpc_resolved_address dummy_resolved_address;
+    memset(&dummy_resolved_address, 0, sizeof(dummy_resolved_address));
+    dummy_resolved_address.len = 123;
+    (*addresses)->emplace_back(dummy_resolved_address, nullptr);
   }
   GRPC_CLOSURE_SCHED(on_done, error);
   return nullptr;

test/core/end2end/fuzzers/api_fuzzer.cc

@@ -342,7 +342,10 @@ static void finish_resolve(void* arg, grpc_error* error) {
       *r->addrs = addrs;
     } else if (r->addresses != nullptr) {
       *r->addresses = grpc_core::MakeUnique<grpc_core::ServerAddressList>();
-      (*r->addresses)->emplace_back(nullptr, 0, nullptr);
+      grpc_resolved_address dummy_resolved_address;
+      memset(&dummy_resolved_address, 0, sizeof(dummy_resolved_address));
+      dummy_resolved_address.len = 0;
+      (*r->addresses)->emplace_back(dummy_resolved_address, nullptr);
     }
     GRPC_CLOSURE_SCHED(r->on_done, GRPC_ERROR_NONE);
   } else {

test/core/iomgr/resolve_address_posix_test.cc

@@ -27,6 +27,8 @@
 #include <grpc/support/sync.h>
 #include <grpc/support/time.h>
 
+#include "src/core/lib/gpr/env.h"
+#include "src/core/lib/gpr/string.h"
 #include "src/core/lib/gpr/useful.h"
 #include "src/core/lib/gprpp/thd.h"
 #include "src/core/lib/iomgr/executor.h"
@@ -163,8 +165,15 @@ int main(int argc, char** argv) {
 
   {
     grpc_core::ExecCtx exec_ctx;
-    test_unix_socket();
-    test_unix_socket_path_name_too_long();
+    char* resolver_env = gpr_getenv("GRPC_DNS_RESOLVER");
+    // c-ares resolver doesn't support UDS (ability for native DNS resolver
+    // to handle this is only expected to be used by servers, which
+    // unconditionally use the native DNS resolver).
+    if (resolver_env == nullptr || gpr_stricmp(resolver_env, "native") == 0) {
+      test_unix_socket();
+      test_unix_socket_path_name_too_long();
+    }
+    gpr_free(resolver_env);
   }
 
   grpc_shutdown();