libpeer does not work in Firefox, and takes ~40s to load in Chrome

[darkuranium]

I strongly suspect the two issues in the title are related, hence grouping them to the same ticket.

I've run into it during the course of implementing #53, and after some investigation, I believe I may have found a clue, which is related to another issue.

---

First, the other issue; (which lead to the clue; I'm putting it here because I believe it's part of the solution, even though it's not the entire one)
The following line in agent.c is a no-op:

  // remove last \n
  description[strlen(description)] = '\0';

Since strlen(description) is the length of the string, foo[strlen(foo)] will always be \0. I assume you meant strlen(description) - 1.

However, there is also a problem in ice_candidate_to_description(...), namely:

  snprintf(description, length, "a=candidate:%d %d %s %" PRIu32 " %d.%d.%d.%d %d typ %s\n",

... I'm pretty sure that should have been a \r\n, which would make the other line strlen(description) - 2.

In other words: (diff minimized for brevity)

--- a/src/ice.c
+++ b/src/ice.c
@@ ... @@ void ice_candidate_to_description(IceCandidate *candidate, char *description, in
-  snprintf(description, length, "a=candidate:%d %d %s %" PRIu32 " %d.%d.%d.%d %d typ %s\n",
+  snprintf(description, length, "a=candidate:%d %d %s %" PRIu32 " %d.%d.%d.%d %d typ %s\r\n",

--- a/src/agent.c
+++ b/src/agent.c
@@ ... @@ void agent_get_local_description(Agent *agent, char *description, int length) {
   // remove last \n
-  description[strlen(description)] = '\0';
+  description[strlen(description) - 2] = '\0';

---

Fixing the above issue reveals an error message in Firefox (as opposed to it simply dropping the connection after a few seconds):

Uncaught (in promise) DOMException: SIPCC Failed to parse SDP: SDP Parse Error on line 17: Warning: Invalid token ordering detected, token c= found after token a=
SDP Parse Error on line 29: Warning: Invalid token ordering detected, token c= found after token a=
SDP Parse Error on line 29: c= line specified twice at same level, parse failed.
SDP Parse Error on line 46: End of line beyond end of buffer.

... comparing with other (working) WebRTC implementations, it looks the c=... line must immediately follow the m=... line, whereas libpeer intermixes them:

libpeer (non-working)

...
m=application 50712 UDP/DTLS/SCTP webrtc-datachannel
a=mid:datachannel
a=sctp-port:5000
c=IN IP4 0.0.0.0
... (other a=... entries)

https://test.antmedia.io:5443/LiveApp/webrtc-test-tool.html (working)

...
m=application 9 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 0.0.0.0
... (other a=... entries)

I'll continue the investigation, but perhaps this'll be useful to someone in the meantime.

[darkuranium]

I got it working!

Above fixes lead me to the ultimate one, which is to add STUN_ATTR_TYPE_XOR_MAPPED_ADDRESS to STUN mappings. (I've implemented this in agent.c)

It's still not a full solution — it makes the prflx candidate work, but not host candidates. That might be a feature of Firefox though, as I have this vague memory that Firefox rejects all such candidates on LAN for privacy and/or security reasons. I'm not 100%, I'll have to investigate this further. But I do have a working solution now!

[darkuranium]

See #60