Panic due to double channel close in Streamer.Stream()

[onitake]

In Streamer.Stream(), there is an inherent concurrency issue, because the Connection.Closed flag is used to determine if the Connection.Queue channel needs to be closed or not:

restreamer/streaming/streamer.go

Lines 334 to 336 in 6a701ca

	if !request.Connection.Closed {
	close(request.Connection.Queue)
	}

If someone closes the channel, the flag update is delayed, and a concurrent goroutine may try to close it again:

restreamer/streaming/connection.go

Line 132 in 6a701ca

conn.Closed = true

As quick&dirty workaround, recover() can be used, but it would be better to remove this flag and find a different way to signal closure and trigger cleanup.