Refactor default host name resolution

Rephrase API's such that resolvers are constrained to be able to provide a
default host given just the text of the URI channel target.

This avoids needing to rewrite such details in the core library during
retries, and generally makes things much saner to debug.

2 files changed, 28 insertions, 4 deletions

diff --git a/src/core/surface/channel.c b/src/core/surface/channel.c
index e50251566d..7378929ca4 100644
--- a/src/core/surface/channel.c
+++ b/src/core/surface/channel.c
@@ -40,6 +40,7 @@
 #include <grpc/support/log.h>
 #include <grpc/support/string_util.h>
 
+#include "src/core/client_config/resolver_registry.h"
 #include "src/core/iomgr/iomgr.h"
 #include "src/core/support/string.h"
 #include "src/core/surface/call.h"
@@ -70,6 +71,7 @@ struct grpc_channel {
   grpc_mdstr *grpc_message_string;
   grpc_mdstr *path_string;
   grpc_mdstr *authority_string;
+  grpc_mdelem *default_authority;
   /** mdelem for grpc-status: 0 thru grpc-status: 2 */
   grpc_mdelem *grpc_status_elem[NUM_CACHED_STATUS_ELEMS];
 
@@ -134,10 +136,27 @@ grpc_channel *grpc_channel_create_from_filters(
         } else {
           channel->max_message_length = args->args[i].value.integer;
         }
+      } else if (0 == strcmp(args->args[i].key, GRPC_ARG_DEFAULT_AUTHORITY)) {
+        if (args->args[i].type != GRPC_ARG_STRING) {
+          gpr_log(GPR_ERROR, "%s: must be an string",
+                  GRPC_ARG_DEFAULT_AUTHORITY);
+        } else {
+          channel->default_authority = grpc_mdelem_from_strings(
+              mdctx, ":authority", args->args[i].value.string);
+        }
       }
     }
   }
 
+  if (channel->is_client && channel->default_authority == NULL) {
+    char *default_authority = grpc_get_default_authority(target);
+    if (default_authority) {
+      channel->default_authority = grpc_mdelem_from_strings(
+          channel->metadata_context, ":authority", default_authority);
+    }
+    gpr_free(default_authority);
+  }
+
   grpc_channel_stack_init(filters, num_filters, channel, args,
                           channel->metadata_context,
                           CHANNEL_STACK_FROM_CHANNEL(channel));
@@ -161,6 +180,8 @@ static grpc_call *grpc_channel_create_call_internal(
   send_metadata[num_metadata++] = path_mdelem;
   if (authority_mdelem != NULL) {
     send_metadata[num_metadata++] = authority_mdelem;
+  } else if (channel->default_authority != NULL) {
+    send_metadata[num_metadata++] = GRPC_MDELEM_REF(channel->default_authority);
   }
 
   return grpc_call_create(channel, parent_call, propagation_mask, cq, NULL,
@@ -251,6 +272,9 @@ static void destroy_channel(void *p, int ok) {
     }
     gpr_free(rc);
   }
+  if (channel->default_authority != NULL) {
+    GRPC_MDELEM_UNREF(channel->default_authority);
+  }
   grpc_mdctx_unref(channel->metadata_context);
   gpr_mu_destroy(&channel->registered_call_mu);
   gpr_free(channel->target);
diff --git a/src/core/surface/init.c b/src/core/surface/init.c
index d9044549f2..0d48cd42d7 100644
--- a/src/core/surface/init.c
+++ b/src/core/surface/init.c
@@ -86,11 +86,11 @@ void grpc_init(void) {
   if (++g_initializations == 1) {
     gpr_time_init();
     grpc_resolver_registry_init("dns:///");
-    grpc_register_resolver_type("dns", grpc_dns_resolver_factory_create());
-    grpc_register_resolver_type("ipv4", grpc_ipv4_resolver_factory_create());
-    grpc_register_resolver_type("ipv6", grpc_ipv6_resolver_factory_create());
+    grpc_register_resolver_type(grpc_dns_resolver_factory_create());
+    grpc_register_resolver_type(grpc_ipv4_resolver_factory_create());
+    grpc_register_resolver_type(grpc_ipv6_resolver_factory_create());
 #ifdef GPR_POSIX_SOCKET
-    grpc_register_resolver_type("unix", grpc_unix_resolver_factory_create());
+    grpc_register_resolver_type(grpc_unix_resolver_factory_create());
 #endif
     grpc_register_tracer("channel", &grpc_trace_channel);
     grpc_register_tracer("surface", &grpc_surface_trace);