lavf/avio: add a ffio_realloc_buf API for AVIO buffer realloc

Add new API ffio_realloc_buf for AVIO buffer realloc.
Signed-off-by: Zhongxing Jiang <tomajsjiang@tencent.com>

libavformat/avio_internal.h

@@ -86,6 +86,15 @@ int ffio_read_size(AVIOContext *s, unsigned char *buf, int size);
 /** @warning must be called before any I/O */
 int ffio_set_buf_size(AVIOContext *s, int buf_size);
 
+/**
+ * Reallocate a given buffer for AVIOContext.
+ *
+ * @param s the AVIOContext to realloc.
+ * @param buf_size required new buffer size.
+ * @return 0 on success, a negative AVERROR on failure.
+ */
+int ffio_realloc_buf(AVIOContext *s, int buf_size);
+
 /**
  * Ensures that the requested seekback buffer size will be available
  *

libavformat/aviobuf.c

@@ -1096,6 +1096,37 @@ int ffio_set_buf_size(AVIOContext *s, int buf_size)
     return 0;
 }
 
+int ffio_realloc_buf(AVIOContext *s, int buf_size)
+{
+    uint8_t *buffer;
+    int data_size;
+
+    if (!s->buffer_size)
+        return ffio_set_buf_size(s, buf_size);
+
+    if (buf_size <= s->buffer_size)
+        return 0;
+
+    buffer = av_malloc(buf_size);
+    if (!buffer)
+        return AVERROR(ENOMEM);
+
+    data_size = s->write_flag ? (s->buf_ptr - s->buffer) : (s->buf_end - s->buf_ptr);
+    if (data_size > 0)
+        memcpy(buffer, s->write_flag ? s->buffer : s->buf_ptr, data_size);
+    av_free(s->buffer);
+    s->buffer = buffer;
+    s->orig_buffer_size = buf_size;
+    s->buffer_size = buf_size;
+    s->buf_ptr = s->write_flag ? (s->buffer + data_size) : s->buffer;
+    if (s->write_flag)
+        s->buf_ptr_max = s->buffer + data_size;
+
+    s->buf_end = s->write_flag ? (s->buffer + s->buffer_size) : (s->buf_ptr + data_size);
+
+    return 0;
+}
+
 static int url_resetbuf(AVIOContext *s, int flags)
 {
     av_assert1(flags == AVIO_FLAG_WRITE || flags == AVIO_FLAG_READ);