修改Janus，支持datachannel通过rtp通道传输
Janus的datachannel支持的协议主要是：“DTLS/SCTP”、"UDP/DTLS/SCTP"，而RTP通道使用的是"UDP/TLS/RTP/SAVPF"，修改的思路包括SDP返回的修改，RTP数据包中提取datachannel包对应SSRC的包。
1、给janus_ice_stream结构体添加data的ssrc字段和初始化：
guint32 data_ssrc_peer;
guint32 data_ssrc, sequence_data;
int janus_sdp_process(void *ice_handle, janus_sdp *remote_sdp, gboolean update) 方法中增加如下逻辑：
if(!strcasecmp(m->proto, "UDP/DTLS/SCTP") || !strcasecmp(m->proto, "UDP/TLS/RTP/SAVPF")) {
stream->data_ssrc = janus_random_uint32(); /* FIXME Should we look for conflicts? */
stream->sequence_data = janus_random_uint32();
janus_flags_set(&handle->webrtc_flags, JANUS_ICE_HANDLE_WEBRTC_NEW_DATACHAN_SDP);
janus_flags_clear(&handle->webrtc_flags, JANUS_ICE_HANDLE_WEBRTC_DATA_CHANNELS);//[email protected] add
} else {
janus_flags_clear(&handle->webrtc_flags, JANUS_ICE_HANDLE_WEBRTC_NEW_DATACHAN_SDP);
}2、SDP返回数据：
m->fmts = g_list_append(m->fmts, g_strdup("109"));
janus_sdp_attribute *aa = janus_sdp_attribute_create("rtpmap", "109 google-data/90000");
m->attributes = g_list_append(m->attributes, aa);
m->ptypes = g_list_append(m->ptypes, GINT_TO_POINTER(109));
3、接收RTP数据函数janus_ice_cb_nice_recv中，增加对datachannel的数据处理的逻辑：
if (header->type == 109 || stream->data_ssrc_peer == packet_ssrc){
/* Pass the data to the responsible plugin */
janus_plugin *plugin = (janus_plugin *)handle->app;
if(plugin && plugin->incoming_data &&
!g_atomic_int_get(&handle->app_handle->stopped) &&
!g_atomic_int_get(&handle->destroyed)){
plugin->incoming_data(handle->app_handle, (char *)buf + RTP_HEADER_SIZE, buflen - RTP_HEADER_SIZE);
}
return;
}4、发送RTP数据时，使用RTP通道发送datachannel的数据：
void janus_plugin_relay_data(janus_plugin_session *plugin_session, char *buf, int len) {
if((plugin_session < (janus_plugin_session *)0x1000) || g_atomic_int_get(&plugin_session->stopped) || buf == NULL || len < 1)
return;
janus_ice_handle *handle = (janus_ice_handle *)plugin_session->gateway_handle;
if(!handle || janus_flags_is_set(&handle->webrtc_flags, JANUS_ICE_HANDLE_WEBRTC_STOP)
|| janus_flags_is_set(&handle->webrtc_flags, JANUS_ICE_HANDLE_WEBRTC_ALERT)){
return;
}
#ifdef HAVE_SCTP
if (janus_flags_is_set(&handle->webrtc_flags, JANUS_ICE_HANDLE_WEBRTC_NEW_DATACHAN_SDP)){
janus_ice_relay_data_withrtp(handle, buf, len);//relay daa with rtp only.
}else{
janus_ice_relay_data(handle, buf, len);
}
#else
JANUS_LOG(LOG_WARN, "Asked to relay data, but Data Channels support has not been compiled...\n");
#endif
}
void janus_ice_relay_data_withrtp(janus_ice_handle *handle, char *buf, int len) {
struct timeval now;
if(!handle || handle->queued_packets == NULL || buf == NULL || len < 1){
return;
}
/* Queue this packet */
janus_ice_queued_packet *pkt = g_malloc(sizeof(janus_ice_queued_packet));
pkt->data = g_malloc(RTP_HEADER_SIZE+len+SRTP_MAX_TAG_LEN+4);
janus_rtp_header *header = (janus_rtp_header *)pkt->data;
header->ssrc = (handle->stream->data_ssrc);
header->type = 109;
header->version = 2;
header->markerbit = 1;
header->extension = 0;
handle->stream->sequence_data++;
header->seq_number = (handle->stream->sequence_data + 100);
gettimeofday(&now,0);
header->timestamp = htonl(now.tv_sec);
memcpy((char *)pkt->data + RTP_HEADER_SIZE, buf, len);
pkt->length = RTP_HEADER_SIZE + len;
pkt->type = JANUS_ICE_PACKET_DATA_WITH_RTP;
pkt->control = FALSE;
pkt->encrypted = FALSE;
pkt->retransmission = FALSE;
pkt->added = janus_get_monotonic_time();
janus_ice_queue_packet(handle, pkt);
}
发送函数static gboolean janus_ice_outgoing_traffic_handle的逻辑中，对ssrc的处理需要修改为：
header->ssrc = htonl(video ? stream->video_ssrc : ((pkt->type == JANUS_ICE_PACKET_DATA_WITH_RTP)?stream->data_ssrc : stream->audio_ssrc));