Drop AI_ADDRCONFIG when resolving TCP addresses

When a system is completely offline (no interface has an IP address but 'lo'),
xcb could not connect to localhost via TCP, e.g. connections with
DISPLAY=127.0.0.1:0 fail.

AI_ADDRCONFIG will only return IPv4 addresses if the system has an IPv4
address configured (likewise for IPv6). This also takes place when
resolving localhost (or 127.0.0.0/8 or ::1). Also, as per RFC 3493,
loopback addresses are not considered as valid addresses when
determining whether to return IPv4 or IPv6 addresses.

As per mailing-list discussion on the xcb list started with message
20110813215405.5818a0c1@x200, the AI_ADDRCONFIG flag is there for historical
reasons:

    In the old days, the "default on-link" assumption in IPv6 made the flag vey
    much indispensable for dual-stack hosts on IPv4-only networks. Without it,
    there would be long timeouts trying non-existent IPv6 connectivity. Nowadays,
    this assumption has been flagged as historic bad practice by IETF, and hosts
    should have been updated to not make it anymore.

    Then AI_ADDRCONFIG became mostly cosmetic: it avoids phony "Protocol family
    not supported" or "Host unreachable" errors while trying to connect to a dual-
    stack mode from a host with no support for source address selection.

    Nowadays, on up-to-date systems, this flag is completely useless. Then again,
    I understood only the very latest MacOS release is "up-to-date" with this
    definition.

diff --git a/src/xcb_util.c b/src/xcb_util.c
index fde4f85..1bde7b7 100644 (file)
--- a/src/xcb_util.c
+++ b/src/xcb_util.c
@@ -277,9 +277,6 @@ static int _xcb_open_tcp(const char *host, char *protocol, const unsigned short
        host = "localhost";
 
     memset(&hints, 0, sizeof(hints));
-#ifdef AI_ADDRCONFIG
-    hints.ai_flags |= AI_ADDRCONFIG;
-#endif
 #ifdef AI_NUMERICSERV
     hints.ai_flags |= AI_NUMERICSERV;
 #endif