Hi,

I created a pull request ( https://github.com/curl/curl/pull/794 ) and
just wanted to give more information about it.

Some time ago I noticed zypper was failing intermittently when
connecting to the opensuse repositories. After some debugging I noticed
curl itself was failing intermittently (with any connection, not related
to opensuse servers). Finally I got some time to work on this and
noticed that curl always tried first an ipv6 connection and, since my
network is not ipv6 ready, it fell back to ipv4 as it should but then
some of these connections returned a "Network is unreachable" error
which was working fixed just by retrying (sometimes, a number of retries
was needed).

In the Curl_is_connected function there's a for loop that checks the
status of two sockets (entries 0 and 1 of conn->tempsock). Sometimes
conn->tempsock has one ipv6 socket, sometimes it has one ipv4 socket and
sometimes it contains both ipv6 and ipv4 sockets . In the last case, one
of the verifyconnect calls was setting error to 101 (Network is
unreachable) and then the ipv4 socket was checked, but it didn't change
the error value, so the error related to the ipv6 connection was returned.

I made it set error to 0 if Curl_socket_ready returned 0 for the ipv4
socket since that means there's still one connection to check and an
error shouldn't be returned.

I tried compiling curl with this patch and it fixed all the problems
with invalid "Network is unreachable" errors.

Greetings,

--
Antonio Larrosa
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