[golang] replace/modify context in StreamServerInterceptor

[flazz...@gmail.com]

Hi,

I'm implementing a StreamServerInterceptor.

func StreamServerInterceptor(srv interface{}, ss grpc.ServerStream, info *grpc.StreamServerInfo, handler grpc.StreamHandler) error {

    // do some stuff, like attach a tracer to the context

    return handler(srv, ss)

}

I can read the inbound ctx from ss.Context() but I can't figure out a way to replace it on the stream with a derivative Context. The best I can thing of is to wrap ss with some other grpc.ServerStream that does what I want. Is this the canonical way to do this?

Thanks,

-Franco

[Qi Zhao]

Yes you can do that. And we recently add https://github.com/grpc/grpc-go/blob/master/tap/tap.go and you can also use that attach your stuff onto the context in the very early stage (so that ss.Context() gets the ctx you expect). But keep in mind they are still EXPERIMENTAL and might be subject to change later. 

Thanks,

-Franco

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Thanks,

-Qi

[Francesco Lazzarino]

Thanks Qi, I'll look into that.

If it helps anyone the wrapper looks like this:

type serverStreamWrapper struct {

ss  grpc.ServerStream

ctx context.Context

}

func (w serverStreamWrapper) Context() context.Context        { return w.ctx }

func (w serverStreamWrapper) RecvMsg(msg interface{}) error   { return w.ss.RecvMsg(msg) }

func (w serverStreamWrapper) SendMsg(msg interface{}) error   { return w.ss.SendMsg(msg) }

func (w serverStreamWrapper) SendHeader(md metadata.MD) error { return w.ss.SendHeader(md) }

func (w serverStreamWrapper) SetHeader(md metadata.MD) error  { return w.ss.SetHeader(md) }

func (w serverStreamWrapper) SetTrailer(md metadata.MD)       { w.ss.SetTrailer(md) }

[akkif...@gmail.com]

Even simpler:

type serverStreamWrapper struct {

grpc.ServerStream

ctx context.Context

}

func (w *serverStreamWrapper) Context() context.Context { return w.ctx }