Grpc-web: Server stream does not detect client's disconnection

[osechet]

In my application, the client requests data that is returned through a stream. But if the client crashes, the server keeps writing into the stream without any error.

[MarcusLongmuir]

Thanks for raising. Can you provide a repro please?

[atamgp]

Hi, I have the same problem. In the stream example a servers pushes and ends the stream. But in this context (which i also have) the server has many clients and sends endless. Clients come and go.
Current behaviour is indeed that when clients are killed the server still sends without getting an error

err := stream.Send(rate)

It should give an error even when a client abruptly gets killed with no clean Close()

Thanks for fixing..

[jsmouret]

Starting from the example server, replace the method in https://github.com/improbable-eng/grpc-web/blob/master/example/go/exampleserver/exampleserver.go with:

func (s *bookService) QueryBooks(bookQuery *library.QueryBooksRequest, stream library.BookService_QueryBooksServer) error {
    for {
        grpclog.Info("sending to", stream)
        err := stream.Send(books[0])
        if err != nil {
            grpclog.Error("got error", err, "from", stream)
            break
        }
        time.Sleep(time.Second)
    }
    grpclog.Info("done with", stream)
    return nil
}

The idea is to send a message every second.

The output from the server looks like:

exampleserver: 2017/11/28 03:29:06 Starting server. http port: 9090, with TLS: false
exampleserver: 2017/11/28 03:29:14 sending to&{0xc0421b4180}
exampleserver: 2017/11/28 03:29:15 sending to&{0xc0421b4180}
exampleserver: 2017/11/28 03:29:16 sending to&{0xc0421b4180}
exampleserver: 2017/11/28 03:29:17 sending to&{0xc0421b4180}  # Reloading the webpage
exampleserver: 2017/11/28 03:29:17 sending to&{0xc0421d8180}  # Note that there are now 2 different clients
exampleserver: 2017/11/28 03:29:18 sending to&{0xc0421b4180}
exampleserver: 2017/11/28 03:29:18 sending to&{0xc0421d8180}
exampleserver: 2017/11/28 03:29:19 sending to&{0xc0421b4180}  # Reloading again
exampleserver: 2017/11/28 03:29:19 sending to&{0xc0421d8180}  # 3 clients and no errors
exampleserver: 2017/11/28 03:29:19 sending to&{0xc04222a280}
exampleserver: 2017/11/28 03:29:20 sending to&{0xc0421b4180}
exampleserver: 2017/11/28 03:29:20 sending to&{0xc0421d8180}
exampleserver: 2017/11/28 03:29:20 sending to&{0xc04222a280}
exampleserver: 2017/11/28 03:29:21 sending to&{0xc0421b4180}
exampleserver: 2017/11/28 03:29:21 sending to&{0xc0421d8180}
exampleserver: 2017/11/28 03:29:21 sending to&{0xc04222a280}
exampleserver: 2017/11/28 03:29:22 sending to&{0xc0421b4180}
exampleserver: 2017/11/28 03:29:22 sending to&{0xc0421d8180}
exampleserver: 2017/11/28 03:29:22 sending to&{0xc04222a280}

Thank you

[jsmouret]

Workaround is to check the stream context:

err = stream.Context().Err()
if err != nil {
    break
}

[easyCZ]

Closing due to inactivity. Please comment if you'd like to revisit this issue.

[lukaszx0]

The workaround provided by @jsmouret does indeed work, but shouldn't err := stream.Send(e); return error when browser closed connection and there's nothing to write to as stream should be closed at this point? Reproducing it should be very simple using @jsmouret ticker example on server side and opening a browser tab which opens the stream and then closing the tab - server will continue writing to stream, without rising an error unless you'll check Context() explicit.

@easyCZ thoughts?

[raliste]

Anything like http CloseNotify?

[Virtual-felix]

I have the exact same issue but I would like to handle it in the proxy server, in which I don't have access to the stream handler so I can't put this work around.
I tried to create a grpc.StreamServerInterceptor, in which I wrapped the grpc.ServerStream in a wrapper that override the method SendMsg, I wanted to get the context from this method and do something but the context doesn't return any errors even if the client has crashed or closed the tab.
Any suggestions ?