Is it possible to make GRPC_OP_RECV_MESSAGE optional on client side

[Ram]

Team gRPC,

We've a scenario where a gRPC client sets up all the operations and does a grpc_call_start_batch(), something like this:

https://github.com/grpc/grpc/blob/master/test/core/end2end/tests/trailing_metadata.cc#L153
memset(ops, 0, sizeof(ops));
op = ops;
op->op = GRPC_OP_SEND_INITIAL_METADATA;
op->data.send_initial_metadata.count = 2;
....

<snip>

......

op->op = GRPC_OP_RECV_INITIAL_METADATA;
op->data.recv_initial_metadata.recv_initial_metadata = &initial_metadata_recv;
op->flags = 0;
op->reserved = nullptr;
op++;
op->op = GRPC_OP_RECV_MESSAGE;
op->data.recv_message.recv_message = &response_payload_recv;
op->flags = 0;
op->reserved = nullptr;
op++;

....

<snip>

......

error = grpc_call_start_batch(c, ops, static_cast<size_t>(op - ops), tag(1),
nullptr);

GPR_ASSERT(GRPC_CALL_OK == error);

In some scenarios, the server side sends only initial metadata whereas in some other scenarios it sends a message as well along with initial metadata and the client isn't aware of when one vs the other scenario happens.

Is it possible to wake up client (i.e., event posted on the completion queue) to respond to both scenarios? I tried digging around in test subdir, couldn't find my scenario https://github.com/grpc/grpc/tree/master/test 

Any pointers or alternative options on this will be of help, thank you!

Best, -Ram.

[Ram]

Any comments on the feasibility of this or other options to explore? Thank you.

[Michael Lumish]

The simplest way to handle this is to put the GRPC_OP_RECV_MESSAGE into a separate batch. You can wait for the batch with the metadata, then wait for the message batch. If the server ends the call without sending a message, the message batch will end with a null message.

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[Sivaram Kumar Battu]

Thank you Michael, will check if we can restructure the client to handle GRPC_OP_RECV_MESSAGE into a separate batch.

Best, -Ram.