Reintroduce DNS-based cases to dualstack_socket_test.c.

These were dropped before the initial release because they depended on
a hostname that was only resolvable inside Google.  The newer
unittest.grpc.io domain is publicly accessible.

Allow the tests to be skipped, just in case someone is running an
isolated machine, or a DNS resolver that doesn't permit external domains
to return loopback addresses.

1 files changed, 29 insertions, 0 deletions

diff --git a/test/core/end2end/dualstack_socket_test.c b/test/core/end2end/dualstack_socket_test.c
index fcc12952bf..7da80886e1 100644
--- a/test/core/end2end/dualstack_socket_test.c
+++ b/test/core/end2end/dualstack_socket_test.c
@@ -40,6 +40,7 @@
 #include <grpc/support/string_util.h>
 
 #include "src/core/support/string.h"
+#include "src/core/iomgr/resolve_address.h"
 #include "src/core/iomgr/socket_utils_posix.h"
 
 #include "test/core/end2end/cq_verifier.h"
@@ -263,6 +264,15 @@ void test_connect(const char *server_host, const char *client_host, int port,
   gpr_free(details);
 }
 
+int external_dns_works(const char *host) {
+  grpc_resolved_addresses *res = grpc_blocking_resolve_address(host, "80");
+  if (res != NULL) {
+    gpr_free(res);
+    return 1;
+  }
+  return 0;
+}
+
 int main(int argc, char **argv) {
   int do_ipv6 = 1;
 
@@ -308,6 +318,25 @@ int main(int argc, char **argv) {
       test_connect("::1", "ipv4:127.0.0.1", 0, 0);
       test_connect("127.0.0.1", "ipv6:[::1]", 0, 0);
     }
+
+    if (!external_dns_works("loopback46.unittest.grpc.io")) {
+      gpr_log(GPR_INFO, "Skipping tests that depend on *.unittest.grpc.io.");
+    } else {
+      test_connect("loopback46.unittest.grpc.io",
+                   "loopback4.unittest.grpc.io", 0, 1);
+      test_connect("loopback4.unittest.grpc.io",
+                   "loopback46.unittest.grpc.io", 0, 1);
+      if (do_ipv6) {
+        test_connect("loopback46.unittest.grpc.io",
+                     "loopback6.unittest.grpc.io", 0, 1);
+        test_connect("loopback6.unittest.grpc.io",
+                     "loopback46.unittest.grpc.io", 0, 1);
+        test_connect("loopback4.unittest.grpc.io",
+                     "loopback6.unittest.grpc.io", 0, 0);
+        test_connect("loopback6.unittest.grpc.io",
+                     "loopback4.unittest.grpc.io", 0, 0);
+      }
+    }
   }
 
   grpc_shutdown();