example-bot: attempt at returning encrypted messages

Signed-off-by: Maxime “pep” Buquet <pep@bouah.net>

examples/echo_client.py

@@ -36,6 +36,8 @@ class EchoBot(ClientXMPP):
     slixmpp repository.
     """
 
+    eme_ns = 'eu.siacs.conversations.axolotl'
+
     def __init__(self, jid, password):
         ClientXMPP.__init__(self, jid, password)
 
@@ -140,9 +142,30 @@ class EchoBot(ClientXMPP):
     async def encrypted_reply(self, original_msg, body) -> None:
         """Helper to reply with encrypted messages"""
 
-        # TODO: Send the message encrypted.
-        return await self.plain_reply(msg, body)
+        mto = original_msg['from']
+        mtype = original_msg['type']
+        msg = self.make_message(mto=mto, mtype=mtype)
+        msg['eme']['namespace'] = self.eme_ns
+        msg['eme']['name'] = self['xep_0380'].mechanisms[self.eme_ns]
 
+        while True:
+            try:
+                # `encrypt_message` excepts the plaintext to be sent, a list of
+                # bare JIDs to encrypt to, and optionally a dict of problems to
+                # expect per bare JID.
+                recipients = [mto]
+                encrypt = await self['xep_0384'].encrypt_message(body, recipients)
+                msg.append(encrypt)
+                return msg.send()
+            except UndecidedException as exn:
+                # The library prevents us from sending a message to an
+                # untrusted/undecided barejid, so we need to make a decision here.
+                # This is where you prompt your user to ask what to do.
+                self['xep_0384'].trust(exn.bare_jid, exn.device, exn.ik)
+            except Exception as exn:
+                break
+
+        return None
 
 if __name__ == '__main__':
     # Setup the command line arguments.