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res_pjsip_session: Always produce offer on re-INVITE without SDP. 

When PJSIP receives a re-INVITE without an SDP offer the INVITE
session library will first call the on_create_offer callback and
if unavailable then use the active negotiated SDP as the offer.

In some cases this would result in a different SDP then was
previously used without an incremented SDP version number. The two
known cases are:

1. Sending an initial INVITE with a set of codecs and having the
remote side answer with a subset. The active negotiated SDP would
have the pruned list but would not have an incremented SDP version
number.

2. Using re-INVITE for unhold. We would modify the active negotiated
SDP but would not increment the SDP version.

To solve these, and potential other unknown cases, the on_create_offer
callback has now been implemented which produces a fresh offer with
incremented SDP version number. This better fits within the model
provided by the INVITE session library.

ASTERISK-28452

Change-Id: I2d81048d54edcb80fe38fdbb954a86f0a58281a1
This commit is contained in:
Joshua C. Colp 2021-02-16 14:33:07 -04:00 committed by George Joseph
parent 88461a23bb
commit 7acb6e2194
1 changed files with 62 additions and 53 deletions
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115
res/res_pjsip_session.c
View File

@ -2762,56 +2762,6 @@ static pj_bool_t session_reinvite_on_rx_request(pjsip_rx_data *rdata)
}
if (!sdp_info->sdp) {
const pjmedia_sdp_session *local;
int i;
ast_queue_unhold(session->channel);
pjmedia_sdp_neg_get_active_local(session->inv_session->neg, &local);
if (!local) {
return PJ_FALSE;
}
/*
* Some devices indicate hold with deferred SDP reinvites (i.e. no SDP in the reinvite).
* When hold is initially indicated, we
* - Receive an INVITE with no SDP
* - Send a 200 OK with SDP, indicating sendrecv in the media streams
* - Receive an ACK with SDP, indicating sendonly in the media streams
*
* At this point, the pjmedia negotiator saves the state of the media direction so that
* if we are to send any offers, we'll offer recvonly in the media streams. This is
* problematic if the device is attempting to unhold, though. If the device unholds
* by sending a reinvite with no SDP, then we will respond with a 200 OK with recvonly.
* According to RFC 3264, if an offerer offers recvonly, then the answerer MUST respond
* with sendonly or inactive. The result of this is that the stream is not off hold.
*
* Therefore, in this case, when we receive a reinvite while the stream is on hold, we
* need to be sure to offer sendrecv. This way, the answerer can respond with sendrecv
* in order to get the stream off hold. If this is actually a different purpose reinvite
* (like a session timer refresh), then the answerer can respond to our sendrecv with
* sendonly, keeping the stream on hold.
*/
for (i = 0; i < local->media_count; ++i) {
pjmedia_sdp_media *m = local->media[i];
pjmedia_sdp_attr *recvonly;
pjmedia_sdp_attr *inactive;
pjmedia_sdp_attr *sendonly;
recvonly = pjmedia_sdp_attr_find2(m->attr_count, m->attr, "recvonly", NULL);
inactive = pjmedia_sdp_attr_find2(m->attr_count, m->attr, "inactive", NULL);
sendonly = pjmedia_sdp_attr_find2(m->attr_count, m->attr, "sendonly", NULL);
if (recvonly || inactive || sendonly) {
pjmedia_sdp_attr *to_remove = recvonly ?: inactive ?: sendonly;
pjmedia_sdp_attr *sendrecv;
pjmedia_sdp_attr_remove(&m->attr_count, m->attr, to_remove);
sendrecv = pjmedia_sdp_attr_create(session->inv_session->pool, "sendrecv", NULL);
pjmedia_sdp_media_add_attr(m, sendrecv);
}
}
return PJ_FALSE;
}
@ -5222,12 +5172,70 @@ static void session_inv_on_rx_offer(pjsip_inv_session *inv, const pjmedia_sdp_se
SCOPE_EXIT_RTN("%s: create_local_sdp failed\n", ast_sip_session_get_name(session));
}
#if 0
static void session_inv_on_create_offer(pjsip_inv_session *inv, pjmedia_sdp_session **p_offer)
{
/* XXX STUB */
struct ast_sip_session *session = inv->mod_data[session_module.id];
const pjmedia_sdp_session *previous_sdp = NULL;
pjmedia_sdp_session *offer;
int i;
if (inv->neg) {
if (pjmedia_sdp_neg_was_answer_remote(inv->neg)) {
pjmedia_sdp_neg_get_active_remote(inv->neg, &previous_sdp);
} else {
pjmedia_sdp_neg_get_active_local(inv->neg, &previous_sdp);
}
}
offer = create_local_sdp(inv, session, previous_sdp);
if (!offer) {
return;
}
ast_queue_unhold(session->channel);
/*
* Some devices indicate hold with deferred SDP reinvites (i.e. no SDP in the reinvite).
* When hold is initially indicated, we
* - Receive an INVITE with no SDP
* - Send a 200 OK with SDP, indicating sendrecv in the media streams
* - Receive an ACK with SDP, indicating sendonly in the media streams
*
* At this point, the pjmedia negotiator saves the state of the media direction so that
* if we are to send any offers, we'll offer recvonly in the media streams. This is
* problematic if the device is attempting to unhold, though. If the device unholds
* by sending a reinvite with no SDP, then we will respond with a 200 OK with recvonly.
* According to RFC 3264, if an offerer offers recvonly, then the answerer MUST respond
* with sendonly or inactive. The result of this is that the stream is not off hold.
*
* Therefore, in this case, when we receive a reinvite while the stream is on hold, we
* need to be sure to offer sendrecv. This way, the answerer can respond with sendrecv
* in order to get the stream off hold. If this is actually a different purpose reinvite
* (like a session timer refresh), then the answerer can respond to our sendrecv with
* sendonly, keeping the stream on hold.
*/
for (i = 0; i < offer->media_count; ++i) {
pjmedia_sdp_media *m = offer->media[i];
pjmedia_sdp_attr *recvonly;
pjmedia_sdp_attr *inactive;
pjmedia_sdp_attr *sendonly;
recvonly = pjmedia_sdp_attr_find2(m->attr_count, m->attr, "recvonly", NULL);
inactive = pjmedia_sdp_attr_find2(m->attr_count, m->attr, "inactive", NULL);
sendonly = pjmedia_sdp_attr_find2(m->attr_count, m->attr, "sendonly", NULL);
if (recvonly || inactive || sendonly) {
pjmedia_sdp_attr *to_remove = recvonly ?: inactive ?: sendonly;
pjmedia_sdp_attr *sendrecv;
pjmedia_sdp_attr_remove(&m->attr_count, m->attr, to_remove);
sendrecv = pjmedia_sdp_attr_create(session->inv_session->pool, "sendrecv", NULL);
pjmedia_sdp_media_add_attr(m, sendrecv);
}
}
*p_offer = offer;
}
#endif
static void session_inv_on_media_update(pjsip_inv_session *inv, pj_status_t status)
{
@ -5356,6 +5364,7 @@ static pjsip_inv_callback inv_callback = {
.on_new_session = session_inv_on_new_session,
.on_tsx_state_changed = session_inv_on_tsx_state_changed,
.on_rx_offer = session_inv_on_rx_offer,
.on_create_offer = session_inv_on_create_offer,
.on_media_update = session_inv_on_media_update,
.on_redirected = session_inv_on_redirected,
};