[grpc design] Never ending bidirectionnal stream use case

[David Audrain]

Hi, 

Our client application and our server will continuously exchange messages:

• Client may send a message containing a gps coordinate every 10 seconds to the server
• Server may send a message containing geolocalized information
• If there is nothing close the client gps position, server sends nothing
• If an incoming information appears close the client gps position, server push a message to the client

We plan to define our service like this:

service Information

  rpc GetInformation(stream ClientPosition) returns (stream GeoInformation);
}

From an implementation point of view, client and server will keep sending and receiving message forever.

They won't call grpc::ClientReaderWriter::WritesDone at any time, or may be only if  grpc::ClientReaderWriter::Write or grpc::ClientReaderWriter::Read return false.

We didn't see any such use case in C++ examples in the github gRPC repository. Stream based examples assumes that client or server will write a sequence of messages, indicate the sequence is finished, then read a sequence as a response. done. 

Is a never ending bidirectionnal stream a valid usage of gRPC ?

Thank you,

David

[David Audrain]

According to this documentation, this is a valid usage.