implement connections:tcp=disabled

This enables an I2P-only node, which disables TCP entirely (instead of
mapping TCP to Tor, which was the only other option that
reveal-IP-address=False would allow).

closes ticket:2824

docs/configuration.rst

@@ -357,7 +357,7 @@ set the ``tub.location`` option described below.
       that defaults to AUTO)
 
     * ``[connections] tcp =`` is set to ``tcp`` (or left as the default),
-      rather than being set to ``tor``
+      rather than being set to ``tor`` or ``disabled``
 
 
 Connection Management
@@ -415,6 +415,12 @@ To hide the Tahoe node's IP address from the servers that it uses, set the
   [connections]
    tcp = tor
 
+You can also disable TCP hints entirely, which would be appropriate when
+running an I2P-only node::
+
+  [connections]
+   tcp = disabled
+
 (Note that I2P does not support connections to normal TCP ports, so
 ``[connections] tcp = i2p`` is invalid)
 

src/allmydata/node.py

@@ -296,6 +296,9 @@ class Node(service.MultiService):
         # then we remember the default mappings from tahoe.cfg
         self._default_connection_handlers = {"tor": "tor", "i2p": "i2p"}
         tcp_handler_name = self.get_config("connections", "tcp", "tcp").lower()
+        if tcp_handler_name == "disabled":
+            self._default_connection_handlers["tcp"] = None
+        else:
             if tcp_handler_name not in handlers:
                 raise ValueError("'tahoe.cfg [connections] tcp='"
                                  " uses unknown handler type '%s'"
@@ -308,7 +311,7 @@ class Node(service.MultiService):
             self._default_connection_handlers["tcp"] = tcp_handler_name
 
         if not self._reveal_ip:
-            if self._default_connection_handlers["tcp"] == "tcp":
+            if self._default_connection_handlers.get("tcp") == "tcp":
                 raise PrivacyError("tcp = tcp, must be set to 'tor'")
 
     def set_tub_options(self):

src/allmydata/test/test_connections.py

@@ -219,6 +219,8 @@ class Connections(unittest.TestCase):
         self.assertEqual(n._default_connection_handlers["tcp"], "tcp")
         self.assertEqual(n._default_connection_handlers["tor"], "tor")
         self.assertEqual(n._default_connection_handlers["i2p"], "i2p")
+        n.set_tub_options()
+        n._create_tub()
 
     def test_tor(self):
         n = FakeNode(BASECONFIG+"[connections]\ntcp = tor\n")
@@ -242,6 +244,15 @@ class Connections(unittest.TestCase):
         self.assertIn("'tahoe.cfg [connections] tcp='", str(e))
         self.assertIn("uses unknown handler type 'unknown'", str(e))
 
+    def test_tcp_disabled(self):
+        n = FakeNode(BASECONFIG+"[connections]\ntcp = disabled\n")
+        n.init_connections()
+        self.assertEqual(n._default_connection_handlers["tcp"], None)
+        self.assertEqual(n._default_connection_handlers["tor"], "tor")
+        self.assertEqual(n._default_connection_handlers["i2p"], "i2p")
+        n.set_tub_options()
+        n._create_tub()
+
 class Privacy(unittest.TestCase):
     def test_flag(self):
         n = FakeNode(BASECONFIG)
@@ -266,6 +277,14 @@ class Privacy(unittest.TestCase):
         e = self.assertRaises(PrivacyError, n.init_connections)
         self.assertEqual(str(e), "tcp = tcp, must be set to 'tor'")
 
+    def test_connections_tcp_disabled(self):
+        n = FakeNode(BASECONFIG+
+                     "[connections]\ntcp = disabled\n"+
+                     "[node]\nreveal-IP-address = false\n")
+        n.check_privacy()
+        n.init_connections() # passes privacy check
+        self.assertEqual(n._default_connection_handlers["tcp"], None)
+
     def test_tub_location_auto(self):
         n = FakeNode(BASECONFIG+"[node]\nreveal-IP-address = false\n")
         n._portnumfile = "missing"