Using GStreamer WebRTC example client with Cowboy WebSocket server: the client stuck in stage "Upgrading to WebSocket"

[akanashin]

Hello!
So, I was using GStreamer WebRTC client as a testing tool for building my own WebRTC/WebSocket video provider. The example performs media negotiation using WebSockets then it establishes WebRTC connection and receives audio/video data.

Now I'm developing WebSocket signalling server in Erlang with Cowboy.
I was able to communicate with the server with my C++ test programs. Connecting/upgrading/message exchange. Everything is OK.

However, example client is unable to work with my Cowboy server. It get stuck in stage "Upgrading to WebSocket".
At the same time the example client works perfectly with my C++ WebSocket server (I have full set of client/server applications written in C++, now I'm trying to rewrite Communication server in Erlang).

I'm not very familiar with example client, I only know that it is JS-based and using webpack 5.88.2. Internally, It starts "proxy" and then client connects to this proxy. Proxy somehow works with target HTTP/WebSocket server (my Cowboy server).
Also what I do know:

• example client detects that port is closed when I'm shutting down my Cowboy server - means it connects to appropriate address
• callbacks init/2 and websocket_init/1 are not called when example client is "Upgrading to WebSocket"

I've googled and AI-ed the situation. The most usable information was that the issue is somehow related to "CORS". That I need to enable it in Cowboy. However, instructions pointed to callback init/2 which is not even called, so I'm at a loss here.

Cowboy module is started with:

Dispatch = cowboy_router:compile([
		{'_', [
			{"/", ss2_ws, []}
		]}
	]),
	{ok, _} = cowboy:start_clear(http, [{port, 8445}], #{
		env => #{dispatch => Dispatch}
	}),

Console output from example client looks like:

[email protected] start
webpack serve

[webpack-dev-server] SSL certificate: .../WORK/webrtc-client-local.ss2/gstwebrtc-api/node_modules/.cache/webpack-dev-server/server.pem
[webpack-dev-server] [HPM] Proxy created: /webrtc -> ws://127.0.0.1:8445
[webpack-dev-server] Project is running at:
[webpack-dev-server] Loopback: https://localhost:9090/
[webpack-dev-server] On Your Network (IPv4): https://192.168.1.165:9090/
[webpack-dev-middleware] wait until bundle finished: /
asset gstwebrtc-api-a72514596bcc7c85d5d0.min.js 503 KiB [emitted] [immutable] (name: gstwebrtc-api)
asset index.html 9.26 KiB [emitted]
runtime modules 27.4 KiB 12 modules
modules by path ./node_modules/ 289 KiB
modules by path ./node_modules/webpack-dev-server/client/ 71.8 KiB 16 modules
modules by path ./node_modules/webrtc-adapter/src/js/ 89.9 KiB 11 modules
modules by path ./node_modules/webpack/hot/.js 5.3 KiB 4 modules
modules by path ./node_modules/html-entities/lib/.js 78.9 KiB 4 modules

• 3 modules
  modules by path ./src/*.js 92.3 KiB
  ./src/index.js 1.39 KiB [built] [code generated]
  ./src/gstwebrtc-api.js 12 KiB [built] [code generated]
  ./src/config.js 1.8 KiB [built] [code generated]
  ./src/com-channel.js 9.03 KiB [built] [code generated]
  ./src/session-state.js 1.18 KiB [built] [code generated]
  ./src/consumer-session.js 7.91 KiB [built] [code generated]
• 4 modules
  webpack 5.88.2 compiled successfully in 957 ms
  [webpack-dev-server] [HPM] Upgrading to WebSocket
  ....
  [webpack-dev-server] [HPM] Upgrading to WebSocket
  [webpack-dev-server] [HPM] Error occurred while proxying request localhost:9090/webrtc to undefined [ECONNREFUSED] (https://nodejs.org/api/errors.html#errors_common_system_errors)

Here I stopped Cowboy server and example client detected it.

I'm not very familiar with all the stuff here so I'd love to have some advises where to look at.

Much appreciated,
Thanks

[essen]

Hey, the best would be to use wireshark to capture the network data and check what it's doing under the hood.

[akanashin]

Thanks. Yes, it looks reasonable. Will check it.

[akanashin]

For future reference: the client wanted to open address "/webrtc" for some reason.
I've added endpoint for this address and this solved the issue.