Merge pull request #11979 from apolcyn/ensure_cancel_with_status_memory_api

Add comment and test for API of a parameter to grpc_call_cancel_with_status

include/grpc/grpc.h

@@ -296,7 +296,11 @@ GRPCAPI grpc_call_error grpc_call_cancel(grpc_call *call, void *reserved);
     If a status has not been received for the call, set it to the status code
     and description passed in.
     Importantly, this function does not send status nor description to the
-    remote endpoint. */
+    remote endpoint.
+    Note that \a description doesn't need be a static string.
+    It doesn't need to be alive after the call to
+    grpc_call_cancel_with_status completes.
+    */
 GRPCAPI grpc_call_error grpc_call_cancel_with_status(grpc_call *call,
                                                      grpc_status_code status,
                                                      const char *description,

src/core/lib/surface/call.c

@@ -644,6 +644,8 @@ static void cancel_with_error(grpc_exec_ctx *exec_ctx, grpc_call *c,
 
 static grpc_error *error_from_status(grpc_status_code status,
                                      const char *description) {
+  // copying 'description' is needed to ensure the grpc_call_cancel_with_status
+  // guarantee that can be short-lived.
   return grpc_error_set_int(
       grpc_error_set_str(GRPC_ERROR_CREATE_FROM_COPIED_STRING(description),
                          GRPC_ERROR_STR_GRPC_MESSAGE,

test/core/end2end/tests/cancel_with_status.c

@@ -25,6 +25,7 @@
 #include <grpc/grpc.h>
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
+#include <grpc/support/string_util.h>
 #include <grpc/support/time.h>
 #include <grpc/support/useful.h>
 #include "src/core/lib/support/string.h"
@@ -138,7 +139,12 @@ static void simple_request_body(grpc_end2end_test_config config,
   error = grpc_call_start_batch(c, ops, num_ops, tag(1), NULL);
   GPR_ASSERT(GRPC_CALL_OK == error);
 
-  grpc_call_cancel_with_status(c, GRPC_STATUS_UNIMPLEMENTED, "xyz", NULL);
+  char *dynamic_string = gpr_strdup("xyz");
+  grpc_call_cancel_with_status(c, GRPC_STATUS_UNIMPLEMENTED,
+                               (const char *)dynamic_string, NULL);
+  // The API of \a description allows for it to be a dynamic/non-const
+  // string, test this guarantee.
+  gpr_free(dynamic_string);
 
   CQ_EXPECT_COMPLETION(cqv, tag(1), 1);
   cq_verify(cqv);