Can't send message on negotiated DataChannel

[cuchaz]

Hello,

I've been trying to set up a connection over a data channel using a negotiated id, but I haven't had much success. The connection will open, but I'm unable to send data channel messages between the endpoints for some reason.

I often see these warnings in the log:

[... DEBUG rtc::peer_connection::handler::sctp] sctp data channel set threshold Low(0) for stream id 5
[... WARN  rtc::peer_connection::handler] SctpHandler.handle_write got error: Stream not existed

After digging through the rtc crates sources for a bit, I found that making a small change solves the issue. On this line:
https://github.com/webrtc-rs/rtc/blob/master/rtc-datachannel/src/data_channel/mod.rs#L74
negating the conditional (ie, pushing the DataChannelOpen on a negotiated channel) solves the issue and the two endpoints can exchange data channel messages with no problems.

Is this the right change to make in this case? Or would that change cause problems for non-negotiated channels?

Thanks,
Jeff

[rainliu]

You can submit PR to solve this issue. Don't worry about non-negotiated channels, if something is broken by this change, integration tests will catch it.

[rainliu]

After reviewed the code, if !config.negotiated is corrected logic for negotiated case.

The correct fix may follow pion's https://github.com/pion/webrtc/blob/87b7c3ec2bd36ffc5f6a7c274c3c3dd11166cee7/datachannel.go#L329, where isAlreadyNegotiated is used for data channel's OnOpen event.