Make get_verifier() wait for _confirm to arrive

This improves the error behavior when --verify is used but there's a
WrongPasswordError: the mismatch is detected before the verifiers are
displayed or confirmation is requested.

It requires that the far end sends a "_confirm" message, which was
introduced in release 0.6.0. Use with older versions (if it doesn't
break for other reasons) will cause a hang.

This patch also deletes test_twisted.Basic.test_verifier_mismatch, since
both sides now detect this on their own. It changes
test_wrong_password() too, since we might now notice the error during
send_data (previously we'd only see it in get_data).

src/wormhole/test/test_twisted.py

@@ -109,11 +109,20 @@ class Basic(ServerBase, unittest.TestCase):
         # * w2 will send w2.PAKE, wait for (and get) w1.PAKE, compute a key,
         #   send w2.CONFIRM, then wait for w1.DATA.
         # * w1 will get w2.PAKE, compute a key, send w1.CONFIRM.
+        # * w1 might also get w2.CONFIRM, and may notice the error before it
+        #   sends w1.CONFIRM, in which case the wait=True will signal an
+        #   error inside _get_master_key() (inside send_data), and d1 will
+        #   errback.
+        #   * but w1 might not see w2.CONFIRM yet, in which case it won't
+        #     errback until we do w1.get_data()
         # * w2 gets w1.CONFIRM, notices the error, records it.
         # * w2 (waiting for w1.DATA) wakes up, sees the error, throws
         # * meanwhile w1 finishes sending its data. w2.CONFIRM may or may not
         #   have arrived by then
+        try:
             yield d1
+        except WrongPasswordError:
+            pass
 
         # When we ask w1 to get_data(), one of two things might happen:
         # * if w2.CONFIRM arrived already, it will have recorded the error.
@@ -167,21 +176,6 @@ class Basic(ServerBase, unittest.TestCase):
         self.assertEqual(dataY, b"data1")
         yield self.doBoth(w1.close(), w2.close())
 
-    @inlineCallbacks
-    def test_verifier_mismatch(self):
-        w1 = Wormhole(APPID, self.relayurl)
-        w2 = Wormhole(APPID, self.relayurl)
-        # we must disable confirmation messages, else the wormholes will
-        # figure out the mismatch by themselves and throw WrongPasswordError.
-        w1._send_confirm = w2._send_confirm = False
-        code = yield w1.get_code()
-        w2.set_code(code+"not")
-        res = yield self.doBoth(w1.get_verifier(), w2.get_verifier())
-        v1, v2 = res
-        self.failUnlessEqual(type(v1), type(b""))
-        self.failIfEqual(v1, v2)
-        yield self.doBoth(w1.close(), w2.close())
-
     @inlineCallbacks
     def test_errors(self):
         w1 = Wormhole(APPID, self.relayurl)

src/wormhole/twisted/transcribe.py

@@ -350,6 +350,15 @@ class Wormhole:
         if self._closed: raise UsageError
         if self._code is None: raise UsageError
         yield self._get_master_key()
+        # If the caller cares about the verifier, then they'll probably also
+        # willing to wait a moment to see the _confirm message. Each side
+        # sends this as soon as it sees the other's PAKE message. So the
+        # sender should see this hot on the heels of the inbound PAKE message
+        # (a moment after _get_master_key() returns). The receiver will see
+        # this a round-trip after they send their PAKE (because the sender is
+        # using wait=True inside _get_master_key, below: otherwise the sender
+        # might go do some blocking call).
+        yield self._msg_get(u"_confirm")
         returnValue(self._verifier)
 
     @inlineCallbacks
@@ -369,7 +378,7 @@ class Wormhole:
                 confkey = self.derive_key(u"wormhole:confirmation")
                 nonce = os.urandom(CONFMSG_NONCE_LENGTH)
                 confmsg = make_confmsg(confkey, nonce)
-                yield self._msg_send(u"_confirm", confmsg)
+                yield self._msg_send(u"_confirm", confmsg, wait=True)
 
     @inlineCallbacks
     def _msg_send(self, phase, body, wait=False):
@@ -396,6 +405,9 @@ class Wormhole:
             return self._signal_error(err)
         self._received_messages[phase] = body
         if phase == u"_confirm":
+            # TODO: we might not have a master key yet, if the caller wasn't
+            # waiting in _get_master_key() when a back-to-back pake+_confirm
+            # message pair arrived.
             confkey = self.derive_key(u"wormhole:confirmation")
             nonce = body[:CONFMSG_NONCE_LENGTH]
             if body != make_confmsg(confkey, nonce):