avio: add a destructor for AVIOContext

Before this commit, AVIOContext is to be freed with a plain av_free(),
which prevents us from adding any deeper structure to it.

(cherry picked from commit 99684f3ae7)
Signed-off-by: James Almer <jamrial@gmail.com>

doc/APIchanges

@@ -15,6 +15,9 @@ libavutil:     2015-08-28
 
 API changes, most recent first:
 
+2017-09-01 - xxxxxxx - lavf 57.80.100 / 57.11.0 - avio.h
+  Add avio_context_free(). From now on it must be used for freeing AVIOContext.
+
 2017-08-08 - xxxxxxx - lavu 55.74.100 - pixdesc.h
   Add AV_PIX_FMT_FLAG_FLOAT pixel format flag.
 

libavformat/avio.h

@@ -467,6 +467,14 @@ AVIOContext *avio_alloc_context(
                   int (*write_packet)(void *opaque, uint8_t *buf, int buf_size),
                   int64_t (*seek)(void *opaque, int64_t offset, int whence));
 
+/**
+ * Free the supplied IO context and everything associated with it.
+ *
+ * @param s Double pointer to the IO context. This function will write NULL
+ * into s.
+ */
+void avio_context_free(AVIOContext **s);
+
 void avio_w8(AVIOContext *s, int b);
 void avio_write(AVIOContext *s, const unsigned char *buf, int size);
 void avio_wl64(AVIOContext *s, uint64_t val);

libavformat/aviobuf.c

@@ -143,6 +143,11 @@ AVIOContext *avio_alloc_context(
     return s;
 }
 
+void avio_context_free(AVIOContext **ps)
+{
+    av_freep(ps);
+}
+
 static void writeout(AVIOContext *s, const uint8_t *data, int len)
 {
     if (!s->error) {
@@ -1123,7 +1128,9 @@ int avio_close(AVIOContext *s)
     else
         av_log(s, AV_LOG_DEBUG, "Statistics: %"PRId64" bytes read, %d seeks\n", s->bytes_read, s->seek_count);
     av_opt_free(s);
-    av_free(s);
+
+    avio_context_free(&s);
+
     return ffurl_close(h);
 }
 
@@ -1356,7 +1363,9 @@ int avio_close_dyn_buf(AVIOContext *s, uint8_t **pbuffer)
     *pbuffer = d->buffer;
     size = d->size;
     av_free(d);
-    av_free(s);
+
+    avio_context_free(&s);
+
     return size - padding;
 }
 
@@ -1399,6 +1408,8 @@ int ffio_close_null_buf(AVIOContext *s)
 
     size = d->size;
     av_free(d);
-    av_free(s);
+
+    avio_context_free(&s);
+
     return size;
 }

libavformat/version.h

@@ -32,7 +32,7 @@
 // Major bumping may affect Ticket5467, 5421, 5451(compatibility with Chromium)
 // Also please add any ticket numbers that you believe might be affected here
 #define LIBAVFORMAT_VERSION_MAJOR  57
-#define LIBAVFORMAT_VERSION_MINOR  79
+#define LIBAVFORMAT_VERSION_MINOR  80
 #define LIBAVFORMAT_VERSION_MICRO 100
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \