[PATCHv3] ident.c: add support for IPv6

[Elia Pinto <gitter.spiros@gmail.com>]

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: Elia Pinto <gitter.spiros@gmail.com>
Helped-by: Jeff King <peff@peff.net>
Helped-by: Eric Sunshine <sunshine@sunshineco.com>
---
This is the third version of the patch ($gmane/280488)
Changes from previous:

- Simplified the implementation, adding the new
function canonical_name (Jeff King) ($gmane/281479).
Fixed a new typo introduced in the second version.

Signed-off-by: Elia Pinto <gitter.spiros@gmail.com>
---
 ident.c | 32 +++++++++++++++++++++++++++-----
 1 file changed, 27 insertions(+), 5 deletions(-)

diff --git a/ident.c b/ident.c
index 5ff1aad..6695537 100644
--- a/ident.c
+++ b/ident.c
@@ -70,10 +70,33 @@ static int add_mailname_host(struct strbuf *buf)
 	return 0;
 }
 
+static int canonical_name(const char *host, struct strbuf *out)
+{
+       int status=-1;
+#ifndef NO_IPV6
+       struct addrinfo hints, *ai;
+       memset (&hints, '\0', sizeof (hints));
+       hints.ai_flags = AI_CANONNAME;
+       int gai = getaddrinfo(host, NULL, &hints, &ai);
+       if (!gai) {
+               if (ai && strchr(ai->ai_canonname, '.')) {
+                       strbuf_addstr(out, ai->ai_canonname);
+                       status=0;
+               }
+               freeaddrinfo(ai);
+       }
+#else
+       struct hostent *he = gethostbyname(buf);
+       if (he && strchr(he->h_name, '.')) {
+                       strbuf_addstr(out, he->h_name);
+                       status=0;
+       }
+#endif /* NO_IPV6 */
+}
+
 static void add_domainname(struct strbuf *out)
 {
 	char buf[1024];
-	struct hostent *he;
 
 	if (gethostname(buf, sizeof(buf))) {
 		warning("cannot get host name: %s", strerror(errno));
@@ -82,10 +105,9 @@ static void add_domainname(struct strbuf *out)
 	}
 	if (strchr(buf, '.'))
 		strbuf_addstr(out, buf);
-	else if ((he = gethostbyname(buf)) && strchr(he->h_name, '.'))
-		strbuf_addstr(out, he->h_name);
-	else
-		strbuf_addf(out, "%s.(none)", buf);
+	else {
+		 if (canonical_name(buf,out) != 0) strbuf_addf(out, "%s.(none)", buf);
+	}
 }
 
 static void copy_email(const struct passwd *pw, struct strbuf *email)
-- 
2.5.0