impl: add client origin metadata for a failed async unary rpc (#14088)

* impl(internal): change the error message for a failed async unary rpc

* address comments

* update comment

* address comment

Author: alevenberg

google/cloud/completion_queue_test.cc

@@ -43,6 +43,7 @@ namespace {
 
 using ::google::cloud::testing_util::FakeCompletionQueueImpl;
 using ::google::cloud::testing_util::IsOk;
+using ::google::cloud::testing_util::StatusIs;
 using ::testing::Contains;
 using ::testing::HasSubstr;
 using ::testing::Not;
@@ -405,7 +406,11 @@ TEST(CompletionQueueTest, MakeRpcsAfterShutdown) {
           },
           r1, std::make_unique<grpc::ClientContext>())
           .then([](future<StatusOr<Response>> f) {
-            EXPECT_EQ(StatusCode::kCancelled, f.get().status().code());
+            auto status = f.get().status();
+            EXPECT_THAT(status, StatusIs(StatusCode::kCancelled));
+            auto const& metadata = status.error_info().metadata();
+            EXPECT_THAT(metadata,
+                        Contains(Pair("gl-cpp.error.origin", "client")));
           });
 
   Request r2;

google/cloud/internal/async_rpc_details.h

@@ -19,6 +19,7 @@
 #include "google/cloud/future.h"
 #include "google/cloud/grpc_error_delegate.h"
 #include "google/cloud/internal/call_context.h"
+#include "google/cloud/internal/make_status.h"
 #include "google/cloud/status_or.h"
 #include "google/cloud/version.h"
 #include "absl/functional/function_ref.h"
@@ -72,8 +73,11 @@ class AsyncUnaryRpcFuture : public AsyncGrpcOperation {
     ScopedCallContext scope(call_context_);
     if (!ok) {
       // `Finish()` always returns `true` for unary RPCs, so the only time we
-      // get `!ok` is after `Shutdown()` was called; treat that as "cancelled".
-      promise_.set_value(Status(StatusCode::kCancelled, "call cancelled"));
+      // get `!ok` is after `Shutdown()` was called; create a "cancelled"
+      // originating from the client.
+      promise_.set_value(internal::CancelledError(
+          "call cancelled",
+          GCP_ERROR_INFO().WithMetadata("gl-cpp.error.origin", "client")));
       return true;
     }
     if (!status_.ok()) {