They very occasionally fail for the same reason:

  Instance of 'UnknownSignedPrekeyException'
  package:omemo_dart/src/omemo/sessionmanager.dart 185:7  OmemoSessionManager._addSessionFromKeyExchange
  ===== asynchronous gap ===========================
  package:omemo_dart/src/omemo/sessionmanager.dart 347:7  OmemoSessionManager.decryptMessage
  ===== asynchronous gap ===========================
  test/omemo_test.dart 254:24                             main.<fn>

Whenever we send a message to an unacked ratchet, we are not supposed to generate a new one but instead just send the old key exchange until we are acked. The message numbering prevents this from being an issue.

See the test Test by sending multiple messages back and forth in test/omemo_test.dart.

Edit: This bug does not seem to be triggered due to a bad ratchet since the Double Ratchet tests do not fail.

Unhandled exception:
Instance of 'InvalidMessageHMACException'
#0      decrypt (package:omemo_dart/src/double_ratchet/crypto.dart:44:5)
<asynchronous suspension>
#1      OmemoSessionManager.decryptMessage.<anonymous closure> (package:omemo_dart/src/omemo/sessionmanager.dart:329:22)
<asynchronous suspension>
#2      BasicLock.synchronized (package:synchronized/src/basic_lock.dart:33:16)
<asynchronous suspension>
#3      OmemoSessionManager.decryptMessage (package:omemo_dart/src/omemo/sessionmanager.dart:324:5)
<asynchronous suspension>
#4      OmemoEncryptionImplementation.decryptStanza (package:xmpp_omemo/src/transformers/message.dart:151:22)
<asynchronous suspension>
#5      OmemoMessageTransformer.transformToData (package:xmpp_omemo/src/transformers/message.dart:198:23)
<asynchronous suspension>
#6      MessageTransformerManager.transformToData (package:xmpp_im/src/transformers/manager.dart:92:22)
<asynchronous suspension>
#7      Stream.asyncMap.<anonymous closure>.add (dart:async/stream.dart:742:7)
<asynchronous suspension

From XEP-0384

Clients MUST NOT use a newly built session to transmit data without user intervention. [...] This rule does not apply to empty OMEMO messages (as per Sending a message) that are used purely to transfer key material, e.g. as part of heartbeat messages or automatic key exchange completion.

• [x] Allow fully deserialising
• [x] Allow fully serialising itself
• [x] Add a commit and load function to allow users to just subclass, override those two functions and use their preferred storage solution
  • This should, however, be optional to provide a memoryless backend
  • This allows us to store ratchets individually, preventing us from having to serialise the entire manager everytime a message is encrypted or decrypted

Replace the OmemoSessionManager interface. Closes #20.

Fixes:

• Build an abstraction over message sending #20.
• Implements heartbeat messages.
• Moves implementation experience from moxxmpp into the library

Message sending a bit more involved since we need to check for new ratchets, handle unacked ratchets and so on. So having this one being handled by omemo_dart would be a huge improvement.