multi: close the connection when h2=>h1 downgradingbagder/h1h2-downgrade-close

Otherwise libcurl is likely to reuse the connection again in the next
attempt since the connection reuse logic doesn't take downgrades into
account.

Reported-by: Anthony Ramine
Fixes #6788

1 files changed, 1 insertions, 0 deletions

diff --git a/lib/multi.c b/lib/multi.c
index f5bacc17c..5de479322 100644
--- a/lib/multi.c
+++ b/lib/multi.c
@@ -2158,6 +2158,7 @@ static CURLMcode multi_runsingle(struct Curl_multi *multi,
 
         if(!ret) {
           infof(data, "Downgrades to HTTP/1.1!\n");
+          connclose(data->conn, "Disconnect HTTP/2 for HTTP/1");
           data->state.httpwant = CURL_HTTP_VERSION_1_1;
           /* clear the error message bit too as we ignore the one we got */
           data->state.errorbuf = FALSE;