[FFmpeg-devel] [PATCH 3/3] Deprecate url_exist() and replace all its uses, use url_check() instead.

[Stefano Sabatini]

The problem with url_exist() is that it tries to open a file in RDONLY
mode. If the file is a FIFO and there is a reading client, the open()
call will hang, and the ffmpeg process will get stuck.

Using url_check() with no access mode of ~0 check if the file simply
exists without attempting to open it, thus avoiding locks.

Fix issue #1663.
---
 ffmpeg.c               |    2 +-
 ffserver.c             |    4 ++--
 libavformat/avformat.h |    3 +++
 libavformat/avio.c     |    2 ++
 libavformat/avio.h     |    3 +++
 libavformat/img2.c     |    6 +++---
 6 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/ffmpeg.c b/ffmpeg.c
index d9812be..23cf46c 100644
--- a/ffmpeg.c
+++ b/ffmpeg.c
@@ -3763,7 +3763,7 @@ static void opt_output_file(const char *filename)
             (strchr(filename, ':') == NULL ||
              filename[1] == ':' ||
              av_strstart(filename, "file:", NULL))) {
-            if (url_exist(filename)) {
+            if (url_check(filename, 0) != AVERROR(ENOENT)) {
                 if (!using_stdin) {
                     fprintf(stderr,"File '%s' already exists. Overwrite ? [y/N] ", filename);
                     fflush(stderr);
diff --git a/ffserver.c b/ffserver.c
index d5d8417..c59c746 100644
--- a/ffserver.c
+++ b/ffserver.c
@@ -3669,7 +3669,7 @@ static void build_feed_streams(void)
     for(feed = first_feed; feed != NULL; feed = feed->next_feed) {
         int fd;
 
-        if (url_exist(feed->feed_filename)) {
+        if (url_check(feed->feed_filename, URL_RDONLY) > 0) {
             /* See if it matches */
             AVFormatContext *s;
             int matches = 0;
@@ -3742,7 +3742,7 @@ static void build_feed_streams(void)
                 unlink(feed->feed_filename);
             }
         }
-        if (!url_exist(feed->feed_filename)) {
+        if (url_check(feed->feed_filename, URL_RDONLY) <= 0) {
             AVFormatContext s1 = {0}, *s = &s1;
 
             if (feed->readonly) {
diff --git a/libavformat/avformat.h b/libavformat/avformat.h
index 0520530..581e6c6 100644
--- a/libavformat/avformat.h
+++ b/libavformat/avformat.h
@@ -54,6 +54,9 @@
 #ifndef FF_API_REGISTER_PROTOCOL
 #define FF_API_REGISTER_PROTOCOL  (LIBAVFORMAT_VERSION_MAJOR < 53)
 #endif
+#ifndef FF_API_URL_EXIST
+#define FF_API_URL_EXIST  (LIBAVFORMAT_VERSION_MAJOR < 53)
+#endif
 
 /**
  * I return the LIBAVFORMAT_VERSION_INT constant.  You got
diff --git a/libavformat/avio.c b/libavformat/avio.c
index ac23d59..befff21 100644
--- a/libavformat/avio.c
+++ b/libavformat/avio.c
@@ -276,6 +276,7 @@ int url_close(URLContext *h)
     return ret;
 }
 
+#if FF_API_URL_EXIST
 int url_exist(const char *filename)
 {
     URLContext *h;
@@ -284,6 +285,7 @@ int url_exist(const char *filename)
     url_close(h);
     return 1;
 }
+#endif
 
 int url_check(const char *url, int flags)
 {
diff --git a/libavformat/avio.h b/libavformat/avio.h
index db5f081..2a4d12e 100644
--- a/libavformat/avio.h
+++ b/libavformat/avio.h
@@ -159,11 +159,14 @@ int64_t url_seek(URLContext *h, int64_t pos, int whence);
  */
 int url_close(URLContext *h);
 
+#if FF_API_URL_EXIST
 /**
  * Return a non-zero value if the resource indicated by url
  * exists, 0 otherwise.
  */
+attribute_deprecated
 int url_exist(const char *url);
+#endif
 
 /**
  * Return a positive value if the resource indicated by url can be
diff --git a/libavformat/img2.c b/libavformat/img2.c
index 7c152cb..8ef70d8 100644
--- a/libavformat/img2.c
+++ b/libavformat/img2.c
@@ -129,11 +129,11 @@ static int find_image_range(int *pfirst_index, int *plast_index,
         if (av_get_frame_filename(buf, sizeof(buf), path, first_index) < 0){
             *pfirst_index =
             *plast_index = 1;
-            if(url_exist(buf))
+            if (url_check(buf, URL_RDONLY) != AVERROR(ENOENT))
                 return 0;
             return -1;
         }
-        if (url_exist(buf))
+        if (url_check(buf, URL_RDONLY) != AVERROR(ENOENT))
             break;
     }
     if (first_index == 5)
@@ -151,7 +151,7 @@ static int find_image_range(int *pfirst_index, int *plast_index,
             if (av_get_frame_filename(buf, sizeof(buf), path,
                                       last_index + range1) < 0)
                 goto fail;
-            if (!url_exist(buf))
+            if (url_check(buf, URL_RDONLY) == AVERROR(ENOENT))
                 break;
             range = range1;
             /* just in case... */
-- 
1.7.1