});
      }, sub {
         my ($fh) = @_;
         # could call $fh->bind etc. here

         15
      };

Example: connect to a UNIX domain socket.

   tcp_connect "unix/", "/tmp/.X11-unix/X0", sub {
      ...
   }

=cut

sub tcp_connect($$$;$) {
   my ($host, $port, $connect, $prepare) = @_;

   # see http://cr.yp.to/docs/connect.html for some background
   # also http://advogato.org/article/672.html

   my %state = ( fh => undef );

   # name/service to type/sockaddr resolution
   resolve_sockaddr $host, $port, 0, 0, 0, sub {
      my @target = @_;

      $state{next} = sub {
         return unless exists $state{fh};

         my $target = shift @target
            or do {
               %state = ();
               return $connect->();
            };

         my ($domain, $type, $proto, $sockaddr) = @$target;

         # socket creation
         socket $state{fh}, $domain, $type, $proto
            or return $state{next}();

         fh_nonblocking $state{fh}, 1;
         
         my $timeout = $prepare && $prepare->($state{fh});

         $timeout ||= 30 if AnyEvent::WIN32;

         $state{to} = AnyEvent->timer (after => $timeout, cb => sub {
            $! = &Errno::ETIMEDOUT;
            $state{next}();
         }) if $timeout;

         # called when the connect was successful, which,
         # in theory, could be the case immediately (but never is in practise)
         my $connected = sub {
            delete $state{ww};
            delete $state{to};

            # we are connected, or maybe there was an error
            if (my $sin = getpeername $state{fh}) {
               my ($port, $host) = unpack_sockaddr $sin;

               my $guard = guard {
                  %state = ();
               };

               $connect->($state{fh}, format_address $host, $port, sub {
                  $guard->cancel;
                  $state{next}();
               });
            } else {
               # dummy read to fetch real error code
               sysread $state{fh}, my $buf, 1 if $! == &Errno::ENOTCONN;
               $state{next}();
            }
         };

         # now connect       
         if (connect $state{fh}, $sockaddr) {
            $connected->();
         } elsif ($! == &Errno::EINPROGRESS # POSIX
                  || $! == &Errno::EWOULDBLOCK
                  # WSAEINPROGRESS intentionally not checked - it means something else entirely
                  || $! == AnyEvent::Util::WSAEINVAL # not convinced, but doesn't hurt
                  || $! == AnyEvent::Util::WSAEWOULDBLOCK) {
            $state{ww} = AnyEvent->io (fh => $state{fh}, poll => 'w', cb => $connected);
         } else {
            $state{next}();
         }
      };

      $! = &Errno::ENXIO;
      $state{next}();
   };

   defined wantarray && guard { %state = () }
}