imap-send: add support for IPv6

Add IPv6 support by implementing name resolution with the
protocol agnostic getaddrinfo(3) API. The old gethostbyname(3)
code is still available when git is compiled with NO_IPV6.

Signed-off-by: Benjamin Kramer <benny.kra@googlemail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

imap-send.c

@@ -982,9 +982,7 @@ static struct store *imap_open_store(struct imap_server_conf *srvc)
 	struct imap_store *ctx;
 	struct imap *imap;
 	char *arg, *rsp;
-	struct hostent *he;
-	struct sockaddr_in addr;
-	int s, a[2], preauth;
+	int s = -1, a[2], preauth;
 	pid_t pid;
 
 	ctx = xcalloc(sizeof(*ctx), 1);
@@ -1021,6 +1019,51 @@ static struct store *imap_open_store(struct imap_server_conf *srvc)
 
 		imap_info("ok\n");
 	} else {
+#ifndef NO_IPV6
+		struct addrinfo hints, *ai0, *ai;
+		int gai;
+		char portstr[6];
+
+		snprintf(portstr, sizeof(portstr), "%hu", srvc->port);
+
+		memset(&hints, 0, sizeof(hints));
+		hints.ai_socktype = SOCK_STREAM;
+		hints.ai_protocol = IPPROTO_TCP;
+
+		imap_info("Resolving %s... ", srvc->host);
+		gai = getaddrinfo(srvc->host, portstr, &hints, &ai);
+		if (gai) {
+			fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(gai));
+			goto bail;
+		}
+		imap_info("ok\n");
+
+		for (ai0 = ai; ai; ai = ai->ai_next) {
+			char addr[NI_MAXHOST];
+
+			s = socket(ai->ai_family, ai->ai_socktype,
+				   ai->ai_protocol);
+			if (s < 0)
+				continue;
+
+			getnameinfo(ai->ai_addr, ai->ai_addrlen, addr,
+				    sizeof(addr), NULL, 0, NI_NUMERICHOST);
+			imap_info("Connecting to [%s]:%s... ", addr, portstr);
+
+			if (connect(s, ai->ai_addr, ai->ai_addrlen) < 0) {
+				close(s);
+				s = -1;
+				perror("connect");
+				continue;
+			}
+
+			break;
+		}
+		freeaddrinfo(ai0);
+#else /* NO_IPV6 */
+		struct hostent *he;
+		struct sockaddr_in addr;
+
 		memset(&addr, 0, sizeof(addr));
 		addr.sin_port = htons(srvc->port);
 		addr.sin_family = AF_INET;
@@ -1040,7 +1083,12 @@ static struct store *imap_open_store(struct imap_server_conf *srvc)
 		imap_info("Connecting to %s:%hu... ", inet_ntoa(addr.sin_addr), ntohs(addr.sin_port));
 		if (connect(s, (struct sockaddr *)&addr, sizeof(addr))) {
 			close(s);
+			s = -1;
 			perror("connect");
+		}
+#endif
+		if (s < 0) {
+			fputs("Error: unable to connect to server.\n", stderr);
 			goto bail;
 		}