bugfix: still check request payload

[abel-von]

the ttrpc golang do not send flagNodata in the request even it is an empty request.

fix #221

[abel-von]

/cc @wllenyj

[wllenyj]

We don't have a test case to verify this ok yet. Previously I was doing compatibility test in my locally.
So some caution is needed.

Are there any compatibility issues between the current implementation and the Golang version?

[abel-von]

The ttrpc-rust checks if there is no data in the request by FLAG_NO_DATA set. but golang version do not set this flag even it has no data

 let no_data = (req_msg.header.flags & FLAG_NO_DATA) == FLAG_NO_DATA;

so even it is an empty request with no data, because golang version do not set FLAG_NO_DATA, we will send an empty message to the stream handler, which is not expected.

        if !no_data {
            // Fake the first data message.
            let msg = GenMessage {
                header: MessageHeader::new_data(stream_id, req.payload.len() as u32),

[wllenyj]

@Tim-Zhang Is there conflict this commit with the changes of #208 ?

[abel-von]

It seems golang version of ttrpc fix the empty payload by checking if the client stream is set. Shall rust version follow that logic?

[abel-von]

https://github.com/containerd/ttrpc/blob/v1.2.4/services.go#L147 @wllenyj @Tim-Zhang

[abel-von]

It seems we do not distinguish StreamingClient or StreamingServer in ttrpc-rust.