bug#17976: 24.3; url-retrieve-synchronously doesn't fallback to IPv4

[Andreas Schwab <schwab@suse.de>]

Juliusz Chroboczek <jch@pps.univ-paris-diderot.fr> writes:

> My machine has both IPv6 and IPv4.  I'm accessing a server that has both
> IPv6 and IPv4, but whose web server listens on IPv4 only.  The web server
> is doing the right thing, sending RST upon IPv6 connection attempts.  Wget
> and telnet do the right thing, they fallback to IPv4:
>
>   $ telnet moule.informatique.univ-paris-diderot.fr 8080
>   Trying 2001:660:3301:8070::40...
>   Trying 194.254.199.40...
>   Connected to moule.informatique.univ-paris-diderot.fr.
>   Escape character is '^]'.
>
> On the other hand, url-retrieve-synchronously returns an empty string.
> Tcpdump shows that it's never even trying IPv4:
>
>   (with-current-buffer
>     (url-retrieve-synchronously
>      "http://moule.informatique.univ-paris-diderot.fr:8080")
>     (buffer-substring (point-min) (point-max)))
>   ""

I cannot reproduce that here.  Emacs is properly falling back to IPv4
and I get the expected contents from this command.

Andreas.

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."