// ProxyStream performs a forward of a gRPC frontend stream to a backend.
func ProxyStream(director StreamDirector, logger grpclog.Logger, frontTrans transport.ServerTransport, frontStream *transport.Stream) {
backendTrans, backendStream, err := backendTransportStream(director, frontStream.Context())
if err != nil {
frontTrans.WriteStatus(frontStream, grpc.Code(err), grpc.ErrorDesc(err))
logger.Printf("proxy: Proxy.handleStream %v failed to allocate backend: %v", frontStream.Method(), err)
return
}
defer backendTrans.CloseStream(backendStream, nil)
// data coming from client call to backend
ingressPathChan := forwardDataFrames(frontStream, backendStream, backendTrans)
// custom header handling *must* be after some data is processed by the backend, otherwise there's a deadlock
headerMd, err := backendStream.Header()
if err == nil && len(headerMd) > 0 {
frontTrans.WriteHeader(frontStream, headerMd)
}
// data coming from backend back to client call
egressPathChan := forwardDataFrames(backendStream, frontStream, frontTrans)
// wait for both data streams to complete.
egressErr := <-egressPathChan
ingressErr := <-ingressPathChan
if egressErr != io.EOF || ingressErr != io.EOF {
logger.Printf("proxy: Proxy.handleStream %v failure during transfer ingres: %v egress: %v", frontStream.Method(), ingressErr, egressErr)
frontTrans.WriteStatus(frontStream, codes.Unavailable, fmt.Sprintf("problem in transfer ingress: %v egress: %v", ingressErr, egressErr))
return
}
// handle trailing metadata
trailingMd := backendStream.Trailer()
if len(trailingMd) > 0 {
frontStream.SetTrailer(trailingMd)
}
frontTrans.WriteStatus(frontStream, backendStream.StatusCode(), backendStream.StatusDesc())
}