[FFmpeg-devel] Patch libavformat/aviobuf.c fixes data loss on named pipe reads

[Rob Meyers]

Submitting a patch to fix a bug in ffmpeg found when reading data from a
named pipe. In our test, a pipe sending twelve bytes in two 6 byte messages
results in the first 10 bytes being lost. We found the problem was
introduced with this commit (2ca48e466675a8a3630061cd2c15325eab8eda97) on
June 30, 2013. In this code, the "dst" pointer is always set to s->buffer,
and earlier message bytes are overwritten by later ones when assembling a
packet from multiple small reads.


diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
index 0a7c39eacd..4e04cb79e0 100644
--- a/libavformat/aviobuf.c
+++ b/libavformat/aviobuf.c
@@ -519,9 +519,7 @@ void avio_write_marker(AVIOContext *s, int64_t time,
enum AVIODataMarkerType typ

 static void fill_buffer(AVIOContext *s)
 {
-    int max_buffer_size = s->max_packet_size ?
-                          s->max_packet_size : IO_BUFFER_SIZE;
-    uint8_t *dst        = s->buf_end - s->buffer + max_buffer_size <
s->buffer_size ?
+    uint8_t *dst        = !s->max_packet_size && s->buf_end - s->buffer <
s->buffer_size ?
                           s->buf_end : s->buffer;
     int len             = s->buffer_size - (dst - s->buffer);