Smarter listenport selection.

Now if we aren't given an explicit port, we always initiate the port search
at 12300 and count upward looking for an available port.

Normally the kernel will assign us a random port, but that's not ideal
in our case because we'd like to use the same port numbers whenever
possible; that avoids piling up crap inside iptables in the (hopefully
unlikely) event that we die without cleaning up correctly.

client.py

@@ -1,4 +1,4 @@
-import struct, socket, select, subprocess
+import struct, socket, select, subprocess, errno
 from ssnet import SockWrapper, Handler, Proxy
 from helpers import *
 
@@ -58,9 +58,28 @@ def main(listenip, remotename, subnets):
     log('Starting sshuttle proxy.\n')
     listener = socket.socket()
     listener.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
-    listener.bind(listenip)
+    if listenip[1]:
+        ports = [listenip[1]]
+    else:
+        ports = xrange(12300,65536)
+    last_e = None
+    bound = False
+    log('Binding:')
+    for port in ports:
+        log(' %d' % port)
+        try:
+            listener.bind((listenip[0], port))
+            bound = True
+            break
+        except socket.error, e:
+            last_e = e
+    log('\n')
+    if not bound:
+        assert(last_e)
+        raise last_e
     listener.listen(10)
-    log('Listening on %r.\n' % (listener.getsockname(),))
+    listenip = listener.getsockname()
+    log('Listening on %r.\n' % (listenip,))
 
     iptables_setup(listenip[1], subnets)