transit: tolerate non-ascii bad handshake

I think somebody was port-scanning the server (or pointed some
non-wormhole client at it), and caused some exceptions in the logs.
These are still bad handshakes, but should be logged normally instead of
throwing exceptions.

src/wormhole/server/transit_server.py

@@ -60,7 +60,7 @@ class TransitConnection(protocol.Protocol):
         self._token_buffer += data
         buf = self._token_buffer
         wanted = len("please relay \n")+32*2
-        if len(buf) < wanted-1 and "\n" in buf:
+        if len(buf) < wanted-1 and b"\n" in buf:
             self.transport.write(b"bad handshake\n")
             log.msg("transit handshake early failure")
             return self.disconnect()

src/wormhole/test/test_server.py

@@ -1159,6 +1159,26 @@ class Transit(ServerBase, unittest.TestCase):
 
         a1.transport.loseConnection()
 
+    @defer.inlineCallbacks
+    def test_binary_handshake(self):
+        ep = clientFromString(reactor, self.transit)
+        a1 = yield connectProtocol(ep, Accumulator())
+
+        binary_bad_handshake = b"\x00\x01\xe0\x0f\n\xff"
+        # the embedded \n makes the server trigger early, before the full
+        # expected handshake length has arrived. A non-wormhole client
+        # writing non-ascii junk to the transit port used to trigger a
+        # UnicodeDecodeError when it tried to coerce the incoming handshake
+        # to unicode, due to the ("\n" in buf) check. This was fixed to use
+        # (b"\n" in buf). This exercises the old failure.
+        a1.transport.write(binary_bad_handshake)
+
+        exp = b"bad handshake\n"
+        yield a1.waitForBytes(len(exp))
+        self.assertEqual(a1.data, exp)
+
+        a1.transport.loseConnection()
+
     @defer.inlineCallbacks
     def test_impatience(self):
         ep = clientFromString(reactor, self.transit)