avformat/http: add ff_http_get_shutdown_status api for check the status of shutdown

this function is used to get the previous shutdown status
when reusing the old connection in block mode.

Signed-off-by: Steven Liu <lq@chinaffmpeg.org>

libavformat/http.c

@@ -304,6 +304,22 @@ fail:
         return location_changed;
     return ff_http_averror(s->http_code, AVERROR(EIO));
 }
+int ff_http_get_shutdown_status(URLContext *h)
+{
+    int ret = 0;
+    HTTPContext *s = h->priv_data;
+
+    /* flush the receive buffer when it is write only mode */
+    char buf[1024];
+    int read_ret;
+    read_ret = ffurl_read(s->hd, buf, sizeof(buf));
+    if (read_ret < 0) {
+        ret = read_ret;
+    }
+
+    return ret;
+}
+
 
 int ff_http_do_new_request(URLContext *h, const char *uri)
 {