TURN REST API: Error parsing API from Janus

[ehfd]

CC @fancycode

Issue number one: The TURN REST API capability provided by the signaling server is not well documented, when one must use TURN with Janus.

nextcloud-spreed-signaling/backend_server.go

Line 180 in 4e34e97

r.HandleFunc("/turn/credentials", b.setComonHeaders(b.getTurnCredentials)).Methods("GET")

Documentation should specify correctly that they should add the turn_rest_api option in Janus pointing to /turn/credentials for janus.jcfg in order to utilze turn_rest_api_key:

nat: {
    stun_server = "stun.myurl.invalid"
    stun_port = 3478
    full_trickle = true
    turn_rest_api = "http://localhost:8080/turn/credentials"
    turn_rest_api_key = "<REDACTED>"
}

Issue number two:

Directly accessing http://localhost:8080/turn/credentials?service=turn&api=<REDACTED>&key=<REDACTED>&username=example (same format as https://github.com/meetecho/janus-gateway/blob/dc8323741043a75537fb770d42ca37498a3d8947/src/turnrest.c#L140) results correctly in:

{"username":"1700000000:example","password":"<REDACTED>","ttl":86400,"uris":["turn:turn.myurl.invalid:3478?transport=udp","turn:turn.myurl.invalid:3478?transport=tcp"]}

But in Janus:

[ERR] [turnrest.c:janus_turnrest_request:198] Couldn't parse response: error on line 1: '[' or '{' expected near end of file
[WARN] [{REDACTED}] Failed to add some remote candidates (added 0, expected 1)

Therefore, the TURN REST API is not usable, possibly an empty response for some reason?

[fancycode]

If you increase the log level in Janus, you should see what was received:
https://github.com/meetecho/janus-gateway/blob/dc8323741043a75537fb770d42ca37498a3d8947/src/turnrest.c#L192-L194

[ehfd]

[5060505176029085] Peer advertised 'actpass' DTLS role, we'll be a DTLS client
[5060505176029085] There are 1 audio, 1 video and 1 data m-lines
[5060505176029085] Setting ICE locally: got OFFER
[5060505176029085] Creating ICE agent (ICE Full mode, controlled)
Sending request: http://localhost:8080/turn/credentials?service=turn&api={REDACTED}&key={REDACTED}&username=2103426825996819
Got 0 bytes from the TURN REST API server

[ERR] [turnrest.c:janus_turnrest_request:198] Couldn't parse response: error on line 1: '[' or '{' expected near end of file[5060505176029085] Adding 10.244.42.121 to the addresses to gather candidates for
[5060505176029085] Parsing m-line #0...
[5060505176029085] ICE ufrag (local):   vq7x

I modified nothing from the request with curl and wget to get the response from http://localhost:8080/turn/credentials?service=turn&api={REDACTED}&key={REDACTED}&username=2103426825996819 and received the adequate response:

{"username":"1737200889:2103426825996819","password":"{REDACTED}","ttl":86400,"uris":["{REDACTED}"]}

Even tried 127.0.0.1 instead of localhost with no avail...