Hold State not considered in _receiveReinvite(request)

[jschwinn]

Bug Report

Your environment

• JsSIP version: 3.13.8

Issue description

While testing, I've encountered the following scenario:

1. Call with 2-way audio is established.
2. JsSIP user initiates hold
3. JsSIP sends REINVITE with a=sendonly
4. JsSIP received OK with a=recvonly and sends ACK, hold state is confirmed and stable
5. Remote UA does a REFER with REPLACES to transfer the call to a conference. This is invisible to JsSIP as it occurs on the far side of a B2BUA. As a result, JsSIP received a REINVITE with a=sendrecv.
6. JsSIP sends OK with a=sendrecv, hold state is out of sync. RTCSession still thinks _localHold is true but 2-way audio is heard
7. JsSIP cannot initiate hold, even though 2-way audio is heard

In _receiveReinvite(), in the section "Request with SDP", this._mangleOffer() is only called if this._late_sdp is true. This issue could be fixed by calling _mangleOffer() when _late_sdp OR _localHold is true. Code block starting at line 2047 in RTCSession.js:

function sendAnswer(desc) {
    const extraHeaders = [`Contact: ${this._contact}`];

    this._handleSessionTimersInIncomingRequest(request, extraHeaders);

    if (this._late_sdp || this._localHold) {
        desc = this._mangleOffer(desc);
    }

    request.reply(200, null, extraHeaders, desc, () => {
        this._status = C.STATUS_WAITING_FOR_ACK;
        this._setInvite2xxTimer(request, desc);
        this._setACKTimer();
    });

    // If callback is given execute it.
    if (typeof data.callback === 'function') {
        data.callback();
    }
}

I'm going to test this change and will report back.

Thanks
Jamie

[jschwinn]

I confirmed that the change fixes the issue.

1. Call with 2-way audio is established.
2. JsSIP user initiates hold
3. JsSIP sends REINVITE with a=sendonly
4. JsSIP received OK with a=recvonly and sends ACK, hold state is confirmed and stable
5. JsSIP received a REINVITE with a=sendrecv
6. JsSIP sends OK with a=sendonly, _localHold is respected and audio cannot be heard
7. JsSIP is able to initiate unhold to reestablish 2-way audio

The alternative way to fix this bug would be call the following at the end of _receiveReinvite(request) after sendAnswer(desc)

this._localHold = false;
this._onunhold('local');

The latter fix is the more useful option for me, but I think the first option is also desirable. I will write a patch that makes the hold behavior configurable when REINVITE is received while on-hold.