static DWORD chunked_get_avail_data(data_stream_t *stream, http_request_t *req)
 {
-    /* Allow reading only from read buffer */
+    chunked_stream_t *chunked_stream = (chunked_stream_t*)stream;
+    DWORD res;
+
+    if(!chunked_stream->chunk_size || chunked_stream->chunk_size == ~0u) {
+        res = start_next_chunk(chunked_stream, req);
+        if(res != ERROR_SUCCESS)
+            return 0;
+    }