Improved error-handling / supplemented documention.

docs/transparent.rst

@@ -1,5 +1,6 @@
 .. _transparent:
 
+====================
 Transparent Proxying
 ====================
 
@@ -20,5 +21,20 @@ destination of the TCP connection.
 At the moment, mitmproxy supports transparent proxying on OSX Lion and above,
 and all current flavors of Linux.
 
+Fully transparent mode
+=======
+By default mitmproxy will use its own local ip address for its server-side connections.
+In case this isn't desired, the --spoof-source-address argument can be used to
+use the client's ip address for server-side connections.
+
+This mode does require root privileges though. There's a wrapper in the examples directory
+called 'mitmproxy_shim.c', which will enable you to use this mode with dropped priviliges.
+It can be used as follows:
+
+gcc examples/mitmproxy_shim.c -o mitmproxy_shim -lcap
+sudo chown root:root mitmproxy_shim
+sudo chmod u+s mitmproxy_shim
+./mitmproxy_shim $(which mitmproxy) -T --spoof-source-address
+
 .. _iptables: http://www.netfilter.org/
 .. _pf: https://en.wikipedia.org/wiki/PF_\(firewall\)

mitmproxy/cmdline.py

@@ -478,7 +478,7 @@ def proxy_options(parser):
     group.add_argument(
         "--spoof-source-address",
         action="store_true", dest="spoof_source_address",
-        help="Use client's IP for the server-side connection"
+        help="Use the client's IP for server-side connections"
     )
 
 def proxy_ssl_options(parser):

mitmproxy/protocol/base.py

@@ -117,9 +117,11 @@ class ServerConnectionMixin(object):
 
         self.server_conn = None
         if self.config.options.spoof_source_address:
-            self.server_conn = models.ServerConnection(server_address, (self.ctx.client_conn.address.host, 0), True)
+            self.server_conn = models.ServerConnection(
+                server_address, (self.ctx.client_conn.address.host, 0), True)
         else:
-            self.server_conn = models.ServerConnection(server_address, (self.config.options.listen_host, 0))
+            self.server_conn = models.ServerConnection(
+                server_address, (self.config.options.listen_host, 0))
 
         self.__check_self_connect()
 
@@ -162,10 +164,11 @@ class ServerConnectionMixin(object):
         self.channel.tell("serverdisconnect", self.server_conn)
 
         if self.config.options.spoof_source_address:
-            self.server_conn = models.ServerConnection(address, (self.ctx.client_conn.address.host, 0), True)
+            self.server_conn = models.ServerConnection(
+                address, (self.ctx.client_conn.address.host, 0), True)
         else:
-            self.server_conn = models.ServerConnection(address, (self.server_conn.source_address.host, 0))
+            self.server_conn = models.ServerConnection(
-
+                address, (self.server_conn.source_address.host, 0))
 
     def connect(self):
         """

netlib/exceptions.py

@@ -58,3 +58,6 @@ class InvalidCertificateException(TlsException):
 
 class Timeout(TcpException):
     pass
+
+class ProtocolException(NetlibException):
+    pass

netlib/tcp.py

@@ -731,10 +731,11 @@ class TCPClient(_Connection):
         try:
             connection = socket.socket(self.address.family, socket.SOCK_STREAM)
             if self.spoof_source_address:
-                if os.geteuid() != 0:
+                try:
-                    raise RuntimeError("Insufficient privileges to set socket option")
-                else:
                     connection.setsockopt(socket.SOL_IP, 19, 1)
+                except socket.error as e:
+                    raise exceptions.ProtocolException(
+                        "Failed to spoof the source address: " + e.strerror)
             if self.source_address:
                 connection.bind(self.source_address())
             connection.connect(self.address())
@@ -874,6 +875,7 @@ class BaseHandler(_Connection):
 
 
 class Counter:
+
     def __init__(self):
         self._count = 0
         self._lock = threading.Lock()