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.

Previous versions depended on having 'sudo' in your PATH.  Now that we can
feel safe that --iptables will clean up properly when you exit, and it
doesn't need to authenticate twice, the advantages of sudo aren't strictly
needed.  Good old 'su' is a reasonable fallback - and everybody has it,
which is nice.

Unfortunately su doesn't let you redirect stdin, so I had to play a stupid
fd trick to make it work.

When it happens, it's probably because the client died and the server hasn't
noticed yet.

Now the sudo iptables subprocess persists for the entire life of sshuttle.
The benefits of this are:

- no need to authenticate again at shutdown (failure of which could cause us
  to not clean up iptables)

- if the main process dies unexpectedly, iptables still gets cleaned up

- the password prompt can happen *before* starting the ssh/server process,
  which means it'll stand out and the password prompt won't be overwritten.

Once again, the buffering gets mixed up with the selecting.  Seems to be the
story of my life.

It seems ssh is kind of stupid and uses a really big SO_SNDBUF (hundreds of
kbytes).  Thus, we can't depend on the socket's output buffer to limit our
latency down to something reasonable.  Instead, limit the amount of data we
can send in a single round trip.

Otherwise a single busy stream can ruin it for everybody.