ICE gathering starts too early

[JesApp]

According to https://tools.ietf.org/html/draft-ietf-rtcweb-jsep-24#section-4.1.9 the ICE gathering process should only start after the local description has been set. However, in my application after calling rawrtc_peer_connection_create, the rawrtc_peer_connection_local_candidate_handler is called before the negotiation_needed_handler, which is where I set the local description and send an offer to the remote peer. Since I am using trickle ICE, the rawrtc_peer_connection_local_candidate_handler just sends the ICE candidates to the remote immediately.

This is a problem, because the remote needs to receive the offer as well as create and set the answer description locally, before remote ICE candidates can be added. (The remote is Firefox 60.0.1)

[lgrahl]

Mh, the gathering process is being started when applying the description, so I can't quite follow you. Can you provide a call graph of relevant RAWRTC functions and event handlers? A backtrace in key places should do.

[JesApp]

Here's the backtrace for the negotiation_needed_handler:

#0  negotiation_needed_handler (arg=0x1420a4 <client_info>) at /home/compiler/robot/src/data.c:122
#1  0x00032ed8 in rawrtc_peer_connection_create_data_channel (channelp=0x152f90, connection=0x152ee0, 
    parameters=0x153018, options=0x0, open_handler=0x167a8 <api_channel_open_handler>, 
    buffered_amount_low_handler=0x14cf4 <default_data_channel_buffered_amount_low_handler>, 
    error_handler=0x14d64 <default_data_channel_error_handler>, 
    close_handler=0x14dd4 <default_data_channel_close_handler>, 
    message_handler=0x168d8 <robot_api_message_handler>, arg=0x152f80)
    at /home/compiler/rawrtc/src/librawrtc/peer_connection.c:1510
#2  0x00015428 in initialise_client () at /home/compiler/robot/src/data.c:95
#3  0x00015278 in data_channel_setup () at /home/compiler/robot/src/data.c:62
#4  0x00017970 in main (argc=1, argv=0xbefffd64) at /home/compiler/robot/src/main.c:47

And here's one for the local_candidate_handler

#0  local_candidate_handler (candidate=0x171110, url=0x0, arg=0x1420a4 <client_info>)
    at /home/compiler/robot/src/data.c:171
#1  0x000314a0 in ice_gatherer_local_candidate_handler (ortc_candidate=0x15c930, url=0x0, arg=0x152ee0)
    at /home/compiler/rawrtc/src/librawrtc/peer_connection.c:377
#2  0x0002c55c in announce_candidate (gatherer=0x153080, re_candidate=0x170e98, url=0x0)
    at /home/compiler/rawrtc/src/librawrtc/ice_gatherer.c:272
#3  0x0002d10c in add_candidate (gatherer=0x153080, address=0xbefffa9c, protocol=RAWRTC_ICE_PROTOCOL_UDP, 
    tcp_type=ICE_TCP_ACTIVE) at /home/compiler/rawrtc/src/librawrtc/ice_gatherer.c:717
#4  0x0002d26c in interface_handler (interface=0x171c5c "wlan0", address=0xbefffa9c, arg=0x153080)
    at /home/compiler/rawrtc/src/librawrtc/ice_gatherer.c:777
#5  0x00050f84 in net_getifaddrs (ifh=0x2d18c <interface_handler>, arg=0x153080) at src/net/ifaddrs.c:56
#6  0x0004f958 in net_if_apply (ifh=0x2d18c <interface_handler>, arg=0x153080) at src/net/net.c:104
#7  0x0002d928 in rawrtc_ice_gatherer_gather (gatherer=0x153080, options=0x153050)
    at /home/compiler/rawrtc/src/librawrtc/ice_gatherer.c:1047
#8  0x000322f8 in rawrtc_peer_connection_set_local_description (connection=0x152ee0, description=0x1708a0)
    at /home/compiler/rawrtc/src/librawrtc/peer_connection.c:1004
#9  0x00015620 in negotiation_needed_handler (arg=0x1420a4 <client_info>) at /home/compiler/robot/src/data.c:131
#10 0x00032ed8 in rawrtc_peer_connection_create_data_channel (channelp=0x152f90, connection=0x152ee0, 
parameters=0x153018, options=0x0, open_handler=0x167a8 <api_channel_open_handler>, 
    buffered_amount_low_handler=0x14cf4 <default_data_channel_buffered_amount_low_handler>, 
    error_handler=0x14d64 <default_data_channel_error_handler>, 
    close_handler=0x14dd4 <default_data_channel_close_handler>, 
    message_handler=0x168d8 <robot_api_message_handler>, arg=0x152f80)
    at /home/compiler/rawrtc/src/librawrtc/peer_connection.c:1510
#11 0x00015428 in initialise_client () at /home/compiler/robot/src/data.c:95
#12 0x00015278 in data_channel_setup () at /home/compiler/robot/src/data.c:62
#13 0x00017970 in main (argc=1, argv=0xbefffd64) at /home/compiler/robot/src/main.c:47

So, if I'm reading this right set_local_description is what ends up calling local_candidate_handler which leads to local_candidate_handler finishing before negotiation_needed_handler and the ICE candidate being sent to the peer before the offer description.
Is this a bug in rawrtc or should I simply send out the offer first, before I set it locally?

[lgrahl]

I see. Yeah, this is a bug and I think we could queue a task to start the gathering process delayed (need to check if we can start the other transports regardless). This is not completely trivial to fix and I'm a little bit busy at the moment.

However, for now you should be able to send the offer directly after creating it. Just make sure you call set_local_description prior to calling set_remote_description. And maybe add a comment referencing this issue in the source code. 🙂