Hi all, I've just post an issue [ARROW-13889] on jira as below. Maybe here is the right place to discuss. ---- I'm trying to implement Flight RPC on RPC framework with protobuf message support in distributed system.
However, the flight rpc is tied to grpc. Classes from grpc used in flight server are: 1. `grpc::ServerContext` used in grpc generated code in parameter, and used to generate `ServerCallContext`. 2. `grpc::Status` used in grpc generated code as return type. 3. `grpc::ServerReaderWriter` and `grpc::ServerReader` used in massive wrapped MessageReader/Writer classes. 1 & 2 are not coupled much with flight, while the third part is the tough work. Shall we introduce an interface class with same semantics to allow anyone implement the writing process to stream, such as `arrow::flight::ServerReaderWriter` and `arrow::flight::ServerReader`. So that, making a shim layer between `FlightServiceImpl` and `FlightServerBase` is possible to decouple flight from grpc, meanwhile taking advantage of its zero-copy messages. All message converting processes can be handled in the shim layer. For example, the function definition of `DoGet` can be `arrow::Status DoGet(ServerCallContext* context, const pb::Ticket* request, ServerWriter<pb::FlightData>* writer)`, which converts pb messages to flight's and call functions from actual business logic implementation from `FlightServerBase` as `Status DoGet(const ServerCallContext& context, const Ticket& request, std::unique_ptr<FlightDataStream>* stream)`. While, the client seems more complex, since the cookie stuff and others. If the idea above is possible, I'll have a exploration on client in depth. ---- The problem, what I'm really facing to, is that I cannot get the grpc generated service, which all zero copy operations are implemented, from the rpc framework which is wrapped from a grpc server running over TCP/TLS though. I need to decouple how the messages and streams are comming to FlightServerBase functions. As far as I've tried, in-process grpc is not an option for me to proxy traffic from wrapped rpc to original grpc flight server, since C++ implemention of in-process grpc, unlike Java, is serializing and deserializing pb messages all the time.
