From 58f0978581bf736ac6888fe3013f0c5ac88bfbdc Mon Sep 17 00:00:00 2001 From: Dmitry Volyntsev Date: Wed, 18 Jan 2012 13:46:37 +0400 Subject: [PATCH] rtsp: Use a random offset for trying to open UDP ports for RTP MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit This avoids (for all practical cases) the issue of reusing the same UDP port as for an earlier connection. If the remote doesn't know the previous session was closed, he might keep on sending packets to that port. If we always start off trying to open the same UDP port, we might get those packets intermixed with the new ones. This is occasionally an issue when testing RTSP stuff with DSS, perhaps also with other servers. Signed-off-by: Martin Storsjö --- libavformat/rtsp.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/libavformat/rtsp.c b/libavformat/rtsp.c index 0e56d37a1f..487e910c17 100644 --- a/libavformat/rtsp.c +++ b/libavformat/rtsp.c @@ -1105,7 +1105,7 @@ int ff_rtsp_make_setup_request(AVFormatContext *s, const char *host, int port, int lower_transport, const char *real_challenge) { RTSPState *rt = s->priv_data; - int rtx = 0, j, i, err, interleave = 0; + int rtx = 0, j, i, err, interleave = 0, port_off; RTSPStream *rtsp_st; RTSPMessageHeader reply1, *reply = &reply1; char cmd[2048]; @@ -1123,7 +1123,14 @@ int ff_rtsp_make_setup_request(AVFormatContext *s, const char *host, int port, /* XXX: we assume the same server is used for the control of each * RTSP stream */ - for (j = rt->rtp_port_min, i = 0; i < rt->nb_rtsp_streams; ++i) { + /* Choose a random starting offset within the first half of the + * port range, to allow for a number of ports to try even if the offset + * happens to be at the end of the random range. */ + port_off = av_get_random_seed() % ((rt->rtp_port_max - rt->rtp_port_min)/2); + /* even random offset */ + port_off -= port_off & 0x01; + + for (j = rt->rtp_port_min + port_off, i = 0; i < rt->nb_rtsp_streams; ++i) { char transport[2048]; /*