From 8da56e12c6f8bc1306d1c5db8818933a6ef013d3 Mon Sep 17 00:00:00 2001 From: Daniel Stenberg Date: Thu, 24 Jun 2010 23:19:27 +0200 Subject: [PATCH] multi_socket: re-use of same socket without notifying app When a hostname resolves to multiple IP addresses and the first one tried doesn't work, the socket for the second attempt may get dropped on the floor, causing the request to eventually time out. The issue is that when using kqueue (as on mac and bsd platforms) instead of select, the kernel removes the first fd from kqueue when it is closed (in trynextip, connect.c:503). Trynextip() then goes on to open a new socket, which gets assigned the same number as the one it just closed. Later in multi.c, socket_cb is not called because the fd is already in multi->sockhash, so the new socket is never added to kqueue. The correct fix is to ensure that socket_cb is called to remove the fd when trynextip() closes the socket, and again to re-add it after singleipsocket(). I'm not sure how to cleanly do that, but the attached patch works around the problem in an admittedly kludgy way by delaying the close to ensure that the newly-opened socket gets a different fd. Daniel's added comment: I didn't spot a way to easily do a nicer fix so I've proceeded with Ben's patch. Bug: http://curl.haxx.se/bug/view.cgi?id=3017819 Patch by: Ben Darnell --- lib/connect.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/lib/connect.c b/lib/connect.c index f917ed595..12e71278e 100644 --- a/lib/connect.c +++ b/lib/connect.c @@ -499,13 +499,18 @@ static bool trynextip(struct connectdata *conn, curl_socket_t sockfd; Curl_addrinfo *ai; - /* first close the failed socket */ - sclose(conn->sock[sockindex]); + /* First clean up after the failed socket. + Don't close it yet to ensure that the next IP's socket gets a different + file descriptor, which can prevent bugs when the curl_multi_socket_action + interface is used with certain select() replacements such as kqueue. */ + curl_socket_t fd_to_close = conn->sock[sockindex]; conn->sock[sockindex] = CURL_SOCKET_BAD; *connected = FALSE; - if(sockindex != FIRSTSOCKET) + if(sockindex != FIRSTSOCKET) { + sclose(fd_to_close); return TRUE; /* no next */ + } /* try the next address */ ai = conn->ip_addr->ai_next; @@ -516,10 +521,12 @@ static bool trynextip(struct connectdata *conn, /* store the new socket descriptor */ conn->sock[sockindex] = sockfd; conn->ip_addr = ai; + sclose(fd_to_close); return FALSE; } ai = ai->ai_next; } + sclose(fd_to_close); return TRUE; }