[PATCHv2] ident.c: add support for IPv6

[Elia Pinto]

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 
Helped-by: Jeff King  
Helped-by: Eric Sunshine 
---
This is the second version of the patch ($gmane/280488)
Changes from previous:

- Simplified the implementation, avoiding the duplication of 
the function add_domainname (Jeff King) ($gmane/280512)

- Fixed a possible memory leak with getaddrinfo (Eric Sunshine)
  ($gmane/280507)


 ident.c | 26 ++
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/ident.c b/ident.c
index 5ff1aad..283e83f 100644
--- a/ident.c
+++ b/ident.c
@@ -73,7 +73,12 @@ static int add_mailname_host(struct strbuf *buf)
 static void add_domainname(struct strbuf *out)
 {
char buf[1024];
+#ifndef NO_IPV6
+   struct addrinfo hints, *ai;
+   int gai;
+#else
struct hostent *he;
+#endif /* NO_IPV6 */
 
if (gethostname(buf, sizeof(buf))) {
warning("cannot get host name: %s", strerror(errno));
@@ -82,10 +87,23 @@ 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{
+#ifndef NO_IPV6
+   memset (, '\0', sizeof (hints));
+   hints.ai_flags = AI_CANONNAME;
+   if (!(gai = getaddrinfo(buf, NULL, , )) && ai && 
strchr(ai->ai_canonname, '.')) 
+   strbuf_addstr(out, ai->ai_canonname);
+#else
+   if ((he = gethostbyname(buf)) && strchr(he->h_name, '.'))
+   strbuf_addstr(out, he->h_name);
+#endif /* NO_IPV6 */
+   else
+   strbuf_addf(out, "%s.(none)", buf);
+
+#ifndef NO_IPV6
+   if (gai) freeaddrinfo(ai);
+#endif /* NO_IPV6 */
+   }
 }
 
 static void copy_email(const struct passwd *pw, struct strbuf *email)
-- 
2.5.0

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Re: [PATCHv2] ident.c: add support for IPv6

[Jeff King]

On Thu, Nov 19, 2015 at 02:54:20PM +0100, Elia Pinto wrote:

> 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 
> Helped-by: Jeff King  
> Helped-by: Eric Sunshine 
> ---
> This is the second version of the patch ($gmane/280488)
> Changes from previous:
> 
> - Simplified the implementation, avoiding the duplication of 
> the function add_domainname (Jeff King) ($gmane/280512)
> 
> - Fixed a possible memory leak with getaddrinfo (Eric Sunshine)
>   ($gmane/280507)

Thanks, this looks much nicer than the last round. I still have a few
comments:

> diff --git a/ident.c b/ident.c
> index 5ff1aad..283e83f 100644
> --- a/ident.c
> +++ b/ident.c
> @@ -73,7 +73,12 @@ static int add_mailname_host(struct strbuf *buf)
>  static void add_domainname(struct strbuf *out)
>  {
>   char buf[1024];
> +#ifndef NO_IPV6
> + struct addrinfo hints, *ai;
> + int gai;
> +#else
>   struct hostent *he;
> +#endif /* NO_IPV6 */

Can we bump these declarations closer to the point of use? I think that
makes it easier to read, as the matching bits are all together.

So this:

> + else{
> +#ifndef NO_IPV6
> + memset (, '\0', sizeof (hints));
> + hints.ai_flags = AI_CANONNAME;
> + if (!(gai = getaddrinfo(buf, NULL, , )) && ai && 
> strchr(ai->ai_canonname, '.')) 
> + strbuf_addstr(out, ai->ai_canonname);
> +#else
> + if ((he = gethostbyname(buf)) && strchr(he->h_name, '.'))
> + strbuf_addstr(out, he->h_name);
> +#endif /* NO_IPV6 */

becomes:

  else {
  #ifndef NO_IPV6
struct addrinfo hints, *ai;
int gai;
if (!(gai = getaddrinfo()...))
  #else
struct hostent *he;
if ((he = gethostbyname()))
  #endif

> + else
> + strbuf_addf(out, "%s.(none)", buf);

This depends on both sides of the #if ending with a hanging "if" clause.
I guess that's OK in such a small function, but I do still wonder if we
can have a helper like:

  static void canonical_name(const char *host, struct strbuf *out)
  {
  #ifndef NO_IPV6
struct addrinfo hints, *ai;
int gai = getaddrinfo(host, NULL, , );
if (!gai && ai && strchr(ai->ai_canonname, '.')) {
strbuf_addstr(out, ai->ai_canonname);
freeaddrinfo(ai);
}
  #else
struct hostent *he = gethostbyname(buf);
if (he && strchr(he->h_name, '.'))
strbuf_addstr(out, he->h_name);
  }

  ...
  canonical_name(buf, out);
  if (!out.len)
strbuf_addf(out, "%s.(none)", buf);

(or possibly have an integer return value from canonical_name instead of
checking the strbuf length).

> +#ifndef NO_IPV6
> + if (gai) freeaddrinfo(ai);
> +#endif /* NO_IPV6 */

Should this be "if (!gai)"?

-Peff
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