[FFmpeg-devel] [PATCH] Fix buffer resizing after probe done.

[Artyom Lebedev]

I have this assert fired after probing done and frames are normally 
read: "av_assert0(len >= s->orig_buffer_size);". Buffer size after 
probing ended up with ~5MB, orig_buffer_size was 64K. This place looks 
like total mess, it definitely has a bug with incorrect len modification 
even if buffer was not resize (failure to do so was ignored as well). I 
did not get what is the purpose of "s->buf_ptr != dst" check as well as 
this assert itself, so I removed them, this code really needs some 
comments there.

>From 332b0059d75953868352eedbc866b112a81d7e9f Mon Sep 17 00:00:00 2001
From: Artyom Lebedev <vagran....@gmail.com>
Date: Wed, 19 Dec 2018 14:28:30 +0200
Subject: [PATCH] Fix buffer resizing after probe done.
To: ffmpeg-devel@ffmpeg.org
---
 libavformat/aviobuf.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
index b867fdd..48ab197 100644
--- a/libavformat/aviobuf.c
+++ b/libavformat/aviobuf.c
@@ -550,7 +550,7 @@ 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->buf_end - s->buffer + max_buffer_size <= s->buffer_size ?
                           s->buf_end : s->buffer;
     int len             = s->buffer_size - (dst - s->buffer);
 
@@ -570,16 +570,16 @@ static void fill_buffer(AVIOContext *s)
     }
 
     /* make buffer smaller in case it ended up large after probing */
-    if (s->read_packet && s->orig_buffer_size && s->buffer_size > s->orig_buffer_size) {
-        if (dst == s->buffer && s->buf_ptr != dst) {
-            int ret = ffio_set_buf_size(s, s->orig_buffer_size);
-            if (ret < 0)
-                av_log(s, AV_LOG_WARNING, "Failed to decrease buffer size\n");
+    if (s->read_packet && s->orig_buffer_size && s->buffer_size > s->orig_buffer_size &&
+        dst == s->buffer) {
 
+        int ret = ffio_set_buf_size(s, s->orig_buffer_size);
+        if (ret < 0) {
+            av_log(s, AV_LOG_WARNING, "Failed to decrease buffer size\n");
+        } else {
             s->checksum_ptr = dst = s->buffer;
+            len = s->orig_buffer_size;
         }
-        av_assert0(len >= s->orig_buffer_size);
-        len = s->orig_buffer_size;
     }
 
     len = read_packet_wrapper(s, dst, len);
-- 
2.7.4

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