@@ -203,6 +203,11 @@ int url_fdopen(ByteIOContext *s, URLContext *h);

 /** @warning must be called before any I/O */

 int url_setbufsize(ByteIOContext *s, int buf_size);

+/** Reset the buffer for reading or writing.

+ * @note Will drop any data currently in the buffer without transmitting it.

+ * @param flags URL_RDONLY to set up the buffer for reading, or URL_WRONLY

+ *        to set up the buffer for writing. */

+int url_resetbuf(ByteIOContext *s, int flags);

 /** @note when opened as read/write, the buffers are only used for

    writing */

@@ -38,11 +38,7 @@ int init_put_byte(ByteIOContext *s,

     s->buffer = buffer;

     s->buffer_size = buffer_size;

     s->buf_ptr = buffer;

-    s->write_flag = write_flag;

-    if (!s->write_flag)

-        s->buf_end = buffer;

-    else

-        s->buf_end = buffer + buffer_size;

+    url_resetbuf(s, write_flag ? URL_WRONLY : URL_RDONLY);

     s->opaque = opaque;

     s->write_packet = write_packet;

     s->read_packet = read_packet;

@@ -534,10 +530,23 @@ int url_setbufsize(ByteIOContext *s, int buf_size)

     s->buffer = buffer;

     s->buffer_size = buf_size;

     s->buf_ptr = buffer;

-    if (!s->write_flag)

-        s->buf_end = buffer;

-    else

-        s->buf_end = buffer + buf_size;

+    url_resetbuf(s, s->write_flag ? URL_WRONLY : URL_RDONLY);

+    return 0;

+}

+

+int url_resetbuf(ByteIOContext *s, int flags)

+{

+    URLContext *h = s->opaque;

+    if ((flags & URL_RDWR) || (h && h->flags != flags && !h->flags & URL_RDWR))

+        return AVERROR(EINVAL);

+

+    if (flags & URL_WRONLY) {

+        s->buf_end = s->buffer + s->buffer_size;

+        s->write_flag = 1;

+    } else {

+        s->buf_end = s->buffer;

+        s->write_flag = 0;

+    }

     return 0;

 }