Merge pull request #17470 from apolcyn/cares_default_prep

Avoid SRV and TXT lookups for localhost

2 files changed, 36 insertions, 2 deletions

diff --git a/src/core/ext/filters/client_channel/resolver/dns/c_ares/dns_resolver_ares.cc b/src/core/ext/filters/client_channel/resolver/dns/c_ares/dns_resolver_ares.cc
index c8425ae336..fc83fc4488 100644
--- a/src/core/ext/filters/client_channel/resolver/dns/c_ares/dns_resolver_ares.cc
+++ b/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();
   }
diff --git a/src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.cc b/src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.cc
index 1b1c2303da..6897756769 100644
--- a/src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.cc
+++ b/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,