This prevents ssh from asking for a password successfully.  Error reported
by Chetan Kunte.

Easiest test: give it an invalid hostname.

Reported by Chetan Kunte.

If your machine is a firewall/router, it affects whether people behind the
router can use your sshuttle connection - in the same way that it affects
whether they can route *anything* through you.  And thus, it should be set
by the admin, not by sshuttle.

sshuttle works fine for the local user either way.

(This also affects MacOS since it's a BSD variant.)

It turns out 'established' doesn't work the way I expected it to from
iptables; it's not stateful.  It just checks the TCP flags to see if the
connection *thinks* it's already established, and follows the rule if so.
That caused the first packet of each new connection to set sent to our
transproxy, but not the subsequent ones, so weird stuff happened.

With this change, any (matching) connection created *after* starting sshuttle
will get forwarded, but pre-existing ones - most importantly, sshuttle's own
ssh connection - will not.

And with this (plus the previous commit), sshuttle works on MacOS, including
10.6!

If you 'telnet localhost 12300' weird things happen; someday we should
probably auto-detect and avoid that altogether.  But meanwhile, catch EPIPE
if it happens (it's irrelevant) and don't barf with a %d data type for a
value that can apparently sometimes be None.

It comes down to this:
   sysctl_set('net.inet.ip.scopedroute', 0)

I say "mostly" because actually it doesn't fix it; sshuttle doesn't know
what to do with the received connection, so there must be a minor bug
remaining somewhere.  I'll fix that next.

Thanks to dkf <dfortunato@gmail.com> on the sshuttle mailing list for
suggesting the magic fix.  He points at this post in particular:
  http://discussions.apple.com/thread.jspa?messageID=11558355&#11558355
that gave him the necessary clue.

as of bup commit bup-0.19-2-gce2ace5.

If the ~/.sshuttle.hosts file does not exist, it triggers the following
error:

       Traceback (most recent call last):
         File "./sshuttle", line 80, in <module>
           sys.exit(hostwatch.hw_main(extra))
         File "/home/def/p/sshuttle/hostwatch.py", line 246, in hw_main
           read_host_cache()
         File "/home/def/p/sshuttle/hostwatch.py", line 41, in read_host_cache
           if e.errno == errno.ENOENT:
       NameError: global name 'errno' is not defined

(This only happened if you run 'sshuttle --hostwatch' from the command line
directly, without passing it through assembler.py.)

That only really stops --auto-nets from working; it's mostly harmless
otherwise.  And apparently some locked-down shared hosts don't let you get
the list of routes.

This has new support for default values in square brackets, so let's use
that.

Reported by Jason Axelson.

Also, add 127.0.0.0/8 to the default list of excludes.  If you want to route
0/0, you almost certainly *don't* want to route localhost to the remote ssh
server's localhost!

Thanks to Edward for the suggestion.

Failing to write to the log sucks, but not as much as failing to clean up
just because stderr disappeared.  So let's catch any IOError exception from
log() and just ignore it.

This should fix a problem reported by Camille Moncelier, which is that
sshuttle firewall entries stick around if your tty dies strangely (eg. your
X server aborts for some reason).

Search the entire python sys.path, not just the directory that argv[0] is
in.  That way if you symlink the sshuttle binary into (for example) ~/bin,
it'll be able to work correctly.

If the server is going to delay us, we'd at least like to know that.

Use try/(try/except)/finally instead.  There was only once case of this.

Thanks to Wayne Scott and nisc for pointing this out.

Pointed out by nisc on github.  If people use an unusual umask or have funny
permissions on /etc/hosts, sshuttle would screw it up.

We also use hardlinks to atomically backup the original /etc/hosts to
/etc/hosts.sbak the first time, rather than manually copying it.  Not sure
why I didn't think of that before.

The list of active sessions might tell us about some hostnames on the local
networks, which we can then add to our subnet list.

Now if you use --auto-hosts (-H), the client will ask the server to spawn a
hostwatcher to add names.  That, in turn, will send names back to the
server, which sends them back to the client, which sends them to the
firewall subprocess, which will write them to /etc/hosts.  Whew!

Only the firewall process can write to /etc/hosts, of course, because only
he's running as root.

Since the name discovery process is kind of slow, we cache the names in
~/.sshuttle.hosts on the remote server.

Right now, most of the names are discovered using nmblookup and smbclient,
as well as by reading the existing entries in /etc/hosts.  What would really
be nice would be to query active directory or mdns somehow... but I don't
really know how those work, so this is what you get for now :)  It's pretty
neat, at least.

This tries to discover local hostnames and prints them to stdout.  Will be
used by the server for auto-hostname tracking.

With this rule, we don't interfere with already-established (or incoming)
connections to routes that we're about to take over.  This is what
happens by default in Linux/iptables.

Now if you do

	./sshuttle -Nr username@myservername

It'll automatically route the "local" subnets (ie., stuff in the routing
table) from myservername.  This is (hopefully a reasonable default setting
for most people.

Reported by Wayne Scott.

Instead, grab our source code, send it over the link, and have python eval
it and then start the server.py main() function.

Strangely, there's now *less* horrible stuff in ssh.py, because we no longer
have to munge around with the PATH environment variable.  And this
significantly reduces the setup required to get sshuttle going.

Based on a suggestion from Wayne Scott.

Since we "almost" support ipfw on MacOS (which I guess might mean FreeBSD
too), the name should be a bit more generic.

Basic forwarding now works on MacOS, assuming you set up ipfw correctly
(ha ha).  I wasted a few hours today trying to figure this out, and I'm *so
very close*, but unfortunately it just didn't work.  Think you can figure it
out?

Related changes:
- don't die if iptables is unavailable
- BSD uses getsockname() instead of SO_ORIGINAL_DST
- non-blocking connect() returns EISCONN once it's connected
- you can't setsockopt IP_TTL more than once

Feature requested by Wayne Scott and Ed Maste.

As requested by a user.

It looked okay in markdown, but some of the text lines were a bit too long.

Oops, got those mixed up with some random other markup format.

If you ran sshuttle from /home/apenwarr/sshuttle/sshuttle, we would
automatically add /home/apenwarr/sshuttle to the PATH before trying to
execute sshuttle on the remote machine.  That way, if you install it in the
same place on two computers, the client would still be able to start the
server.

Someone reported, though, that if they installed the client in
/home/apenwarr/sshuttle/shuttle, and the server in /root/sshuttle/sshuttle,
then used "-r root@servername", it wasn't able to find the program.

Similar problems would happen if you're apenwarr at home and averyp at work.

So what we now do is add *two* directories to the PATH:
/home/apenwarr/sshuttle and $HOME/sshuttle, where $HOME is the value of
$HOME on the *server*, not the client.  So it'll find it in either place.

If the server was having trouble starting, we would print a lot of
unnecessary stuff from iptables.  We shouldn't even have bothered *starting*
iptables if the server was dead anyway.

If we can't communicate with the parent process, he's probably died
unexpectedly; just shut down and don't bother people about it.