From 0c4b60f01044e097d30095ceb3b7c65e57126a8f Mon Sep 17 00:00:00 2001 From: John Ogness Date: Wed, 21 Dec 2011 13:22:03 +0100 Subject: [PATCH] udpsrc: drop dataless UDP packets It is allowed to send/receive UDP packets with no data. When such a packet is available, select() will return with success but ioctl(FIONREAD) will return 0. But a read() must still occur in order to clear off the UDP packet from the queue. This patch will read the dataless packet from the socket. If select() was woken for other reasons (and FIONREAD returns 0), this may result in a UDP packet getting accidentally dropped. But since UDP is not reliable, this is acceptable. NOTE: This patch fixes a nasty bug where sending a dataless UDP packet to a udpsrc instance will cause an infinite loop. https://bugzilla.gnome.org/show_bug.cgi?id=666644 Signed-off-by: John Ogness --- gst/udp/gstudpsrc.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/gst/udp/gstudpsrc.c b/gst/udp/gstudpsrc.c index ec644af00a..dce2c9981a 100644 --- a/gst/udp/gstudpsrc.c +++ b/gst/udp/gstudpsrc.c @@ -483,12 +483,20 @@ retry: IOCTL_SOCKET (udpsrc->sock.fd, FIONREAD, &readsize)) < 0)) goto ioctl_failed; - /* if we get here and there is nothing to read from the socket, the select got - * woken up by activity on the socket but it was not a read. We know someone - * will also do something with the socket so that we don't go into an infinite - * loop in the select(). */ + /* If we get here and the readsize is zero, then either select was woken up + * by activity that is not a read, or a poll error occurred, or a UDP packet + * was received that has no data. Since we cannot identify which case it is, + * we handle all of them. This could possibly lead to a UDP packet getting + * lost, but since UDP is not reliable, we can accept this. */ if (G_UNLIKELY (!readsize)) { + /* try to read a packet (and it will be ignored), + * in case a packet with no data arrived */ + recvfrom (udpsrc->sock.fd, (char *)&slen, 0, 0, &sa.sa, &slen); + + /* clear any error, in case a poll error occurred */ clear_error (udpsrc); + + /* poll again */ goto retry; }