Don't request IPv6 addresses if AI_ADDRCONFIG is specified and the system has no...

diff --git a/libc/netbsd/net/getaddrinfo.c b/libc/netbsd/net/getaddrinfo.c
index f2189fb..1233cb8 100644 (file)
--- a/libc/netbsd/net/getaddrinfo.c
+++ b/libc/netbsd/net/getaddrinfo.c
@@ -335,6 +335,36 @@ str2number(const char *p)
                return -1;
 }
 
+/* Determine whether IPv6 connectivity is available. */
+static int
+_have_ipv6() {
+       /*
+        * Connect a UDP socket to an global unicast IPv6 address. This will
+        * cause no network traffic, but will fail fast if the system has no or
+        * limited IPv6 connectivity (e.g., only a link-local address).
+        */
+       static const struct sockaddr_in6 sin6_test = {
+               /* family, port, flow label */
+               AF_INET6, 0, 0,
+               /* 2000:: */
+               {{{ 0x20, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }}},
+               /* scope ID */
+               0};
+       static const struct sockaddr *sa_test = (struct sockaddr *) &sin6_test;
+       int s = socket(PF_INET6, SOCK_DGRAM, IPPROTO_UDP);
+       if (s < 0)
+               return 0;
+       int ret;
+       do {
+               ret = connect(s, sa_test, sizeof(sin6_test));
+       } while (ret < 0 && errno == EINTR);
+       int have_ipv6 = (ret == 0);
+       do {
+               ret = close(s);
+       } while (ret < 0 && errno == EINTR);
+       return have_ipv6;
+}
+
 int
 getaddrinfo(const char *hostname, const char *servname,
     const struct addrinfo *hints, struct addrinfo **res)
@@ -1274,7 +1304,6 @@ _dns_getaddrinfo(void *rv, void   *cb_data, va_list ap)
 
        name = va_arg(ap, char *);
        pai = va_arg(ap, const struct addrinfo *);
-
        //fprintf(stderr, "_dns_getaddrinfo() name = '%s'\n", name);
 
        memset(&q, 0, sizeof(q));
@@ -1299,15 +1328,20 @@ _dns_getaddrinfo(void *rv, void *cb_data, va_list ap)
                /* prefer IPv6 */
                q.name = name;
                q.qclass = C_IN;
-               q.qtype = T_AAAA;
                q.answer = buf->buf;
                q.anslen = sizeof(buf->buf);
-               q.next = &q2;
-               q2.name = name;
-               q2.qclass = C_IN;
-               q2.qtype = T_A;
-               q2.answer = buf2->buf;
-               q2.anslen = sizeof(buf2->buf);
+               /* If AI_ADDRCONFIG, lookup IPv6 only if we have connectivity */
+               if (!(pai->ai_flags & AI_ADDRCONFIG) || _have_ipv6()) {
+                       q.qtype = T_AAAA;
+                       q.next = &q2;
+                       q2.name = name;
+                       q2.qclass = C_IN;
+                       q2.qtype = T_A;
+                       q2.answer = buf2->buf;
+                       q2.anslen = sizeof(buf2->buf);
+               } else {
+                       q.qtype = T_A;
+               }
                break;
        case AF_INET:
                q.name = name;