Added new --auto-hosts and --seed-hosts options to the client.

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.

client.py

@@ -1,4 +1,4 @@
-import struct, socket, select, subprocess, errno
+import struct, socket, select, subprocess, errno, re
 import helpers, ssnet, ssh
 from ssnet import SockWrapper, Handler, Proxy, Mux, MuxWrapper
 from helpers import *
@@ -76,6 +76,12 @@ class FirewallClient:
         if line != 'STARTED\n':
             raise Fatal('%r expected STARTED, got %r' % (self.argv, line))
 
+    def sethostip(self, hostname, ip):
+        assert(not re.search(r'[^-\w]', hostname))
+        assert(not re.search(r'[^0-9.]', ip))
+        self.pfile.write('HOST %s,%s\n' % (hostname, ip))
+        self.pfile.flush()
+
     def done(self):
         self.pfile.close()
         rv = self.p.wait()
@@ -83,7 +89,7 @@ class FirewallClient:
             raise Fatal('cleanup: %r returned %d' % (self.argv, rv))
 
 
-def _main(listener, fw, use_server, remotename, auto_nets):
+def _main(listener, fw, use_server, remotename, seed_hosts, auto_nets):
     handlers = []
     if use_server:
         if helpers.verbose >= 1:
@@ -122,6 +128,14 @@ def _main(listener, fw, use_server, remotename, auto_nets):
         fw.start()
     mux.got_routes = onroutes
 
+    def onhostlist(hostlist):
+        debug2('got host list: %r\n' % hostlist)
+        for line in hostlist.strip().split():
+            if line:
+                name,ip = line.split(',', 1)
+                fw.sethostip(name, ip)
+    mux.got_host_list = onhostlist
+
     def onaccept():
         sock,srcip = listener.accept()
         dstip = original_dst(sock)
@@ -139,6 +153,10 @@ def _main(listener, fw, use_server, remotename, auto_nets):
             outwrap = ssnet.connect_dst(dstip[0], dstip[1])
         handlers.append(Proxy(SockWrapper(sock, sock), outwrap))
     handlers.append(Handler([listener], onaccept))
+
+    if seed_hosts != None:
+        debug1('seed_hosts: %r\n' % seed_hosts)
+        mux.send(0, ssnet.CMD_HOST_REQ, '\n'.join(seed_hosts))
     
     while 1:
         if use_server:
@@ -165,7 +183,7 @@ def _main(listener, fw, use_server, remotename, auto_nets):
             mux.check_fullness()
 
 
-def main(listenip, use_server, remotename, auto_nets, subnets):
+def main(listenip, use_server, remotename, seed_hosts, auto_nets, subnets):
     debug1('Starting sshuttle proxy.\n')
     listener = socket.socket()
     listener.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
@@ -195,6 +213,7 @@ def main(listenip, use_server, remotename, auto_nets, subnets):
     fw = FirewallClient(listenip[1], subnets)
     
     try:
-        return _main(listener, fw, use_server, remotename, auto_nets)
+        return _main(listener, fw, use_server, remotename,
+                     seed_hosts, auto_nets)
     finally:
         fw.done()