transfer: cap retries of "dead connections" to 5bagder/retrycount

When libcurl retries a connection due to it being "seemingly dead" or by
REFUSED_STREAM, it will now only do it up five times before giving up,
to avoid never-ending loops.

Reported-by: Dima Tisnek
Bug: https://curl.haxx.se/mail/lib-2020-03/0044.html

2 files changed, 7 insertions, 1 deletions

diff --git a/lib/transfer.c b/lib/transfer.c
index e76834eb3..d02baa4c3 100644
--- a/lib/transfer.c
+++ b/lib/transfer.c
@@ -1779,6 +1779,12 @@ CURLcode Curl_retry_request(struct connectdata *conn,
     retry = TRUE;
   }
   if(retry) {
+#define CONN_MAX_RETRIES 5
+    if(conn->retrycount++ >= CONN_MAX_RETRIES) {
+      failf(data, "Connection died, tried %d times before giving up",
+            CONN_MAX_RETRIES);
+      return CURLE_SEND_ERROR;
+    }
     infof(conn->data, "Connection died, retrying a fresh connect\n");
     *url = strdup(conn->data->change.url);
     if(!*url)
diff --git a/lib/urldata.h b/lib/urldata.h
index fbb8b645e..a0e71baca 100644
--- a/lib/urldata.h
+++ b/lib/urldata.h
@@ -1098,7 +1098,7 @@ struct connectdata {
   struct http_connect_state *connect_state; /* for HTTP CONNECT */
   struct connectbundle *bundle; /* The bundle we are member of */
   int negnpn; /* APLN or NPN TLS negotiated protocol, CURL_HTTP_VERSION* */
-
+  int retrycount; /* number of retries on a new connection */
 #ifdef USE_UNIX_SOCKETS
   char *unix_domain_socket;
   BIT(abstract_unix_socket);