maintainer-feedback requested: [Bug 211430] devel/apr1: IPv6 to IPv4 fallback does not work in serf

[bugzilla-noreply at freebsd.org]

Don Lewis <truckman at FreeBSD.org> has reassigned Bugzilla Automation
<bugzilla at FreeBSD.org>'s request for maintainer-feedback to apache at FreeBSD.org:
Bug 211430: devel/apr1:  IPv6 to IPv4 fallback does not work in serf
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=211430



--- Description ---
Created attachment 173081
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=173081&action=edit
patch to modify apr1 poll() emulation to match behavior expected by serf.

serf depends on the poll emulation in apr returning a POLLERR event if a
non-blocking connect() attempt fails in order to trigger an IPv6 -> IPv4
fallback, or a fallback to another address for a multi-homed host.  On FreeBSD,
the poll emulation is done using kqueue, and the result returned by the poll()
emulation is POLLIN + POLLHUP.

connect(4,{ AF_INET6 [xxxx:xxxx:xxxx:xxxx::xxxx]:80 },28) ERR#36 'Operation now
in progress'
gettimeofday({ 1469515046.979614 },0x0) 	 = 0 (0x0)
kevent(3,{ 4,EVFILT_READ,EV_ADD,0x0,0x0,0x805491300 },1,0x0,0,0x0) = 0 (0x0)
kevent(3,{ 4,EVFILT_WRITE,EV_ADD,0x0,0x0,0x805491300 },1,0x0,0,0x0) = 0 (0x0)
kevent(3,0x0,0,{ 4,EVFILT_READ,EV_EOF,NOTE_LOWAT|0x3c,0x0,0x805491300
4,EVFILT_WRITE,EV_EOF,NOTE_LOWAT|0x3c,0x8000,0x805491300 },32,{ 0.500000000 })
= 2 (0x2)

When serf sees this, it calls read(), which then fails with ECONNREFUSED (or
whatever), which is not even a documented read() errno value.

read(4,0x80549c064,8000)			 ERR#61 'Connection refused'

What that occurs, serf closes the socket an any other addresses are not tried.

The attached patch modifies apr to return what serf expects in the case of a
non-blocking connect() failure.  Unfortunately, I did not see an easy way of
handling ETIMEDOUT since that error can either be caused by connect failing or
after the connection is established.  The poll emulation might need to
differentiate between those two cases.

This problem affects users of svn who don't have working IPv6 connectivity to
the FreeBSD svn servers.