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Messenger Communication Protocol

Messenger communications adhere to a set protocol for transmitting messages. The protocol and structure of Messages are defined below. When the word 'Variable' is used, it indicates that the corresponding field has a 4-byte length field appended to the value.

Message

Messenger Messages are a TLV-type structure with an AES-encrypted value of variable length.

+----------------------+----------------------+-----------------------+-------------------------+
|     Message Type     |    Message Length    |   Initialization IV   |   AES Encrypted Value   |
+----------------------+----------------------+-----------------------+-------------------------+
|       4 bytes        |       4 bytes        |       16 bytes        |     Variable length     |
+----------------------+----------------------+-----------------------+-------------------------+

Values

There are several types of values so that Messenger can accomplish the task of establishing TCP connections and sending data.

InitiateForwarderClientReq

+-----------------------------+-----------------------------+-----------------------------+
|     Forwarder Client ID     |         IP Address          |            Port             |
+-----------------------------+-----------------------------+-----------------------------+
|          Variable           |          Variable           |          4 bytes            |
+-----------------------------+-----------------------------+-----------------------------+

InitiateForwarderClientRep

+-----------------------------+-----------------------------+-----------------------------+-----------------------------+-----------------------------+
|     Forwarder Client ID     |         Bind Address        |          Bind Port          |        Address Type         |           Reason            |
+-----------------------------+-----------------------------+-----------------------------+-----------------------------+-----------------------------+
|          Variable           |          Variable           |          4 bytes            |          4 bytes            |          4 bytes            |
+-----------------------------+-----------------------------+-----------------------------+-----------------------------+-----------------------------+

Send Data

+-----------------------------+-----------------------------+
|     Forwarder Client ID     |             Data            |
+-----------------------------+-----------------------------+
|          Variable           |          Variable           |
+-----------------------------+-----------------------------+

Check In

+-----------------------------+
|        Messenger ID         |
+-----------------------------+
|          Variable           |
+-----------------------------+

Communication Flows

Messenger is a client-server application, so there are local and remote versions of Messenger Clients that negotiate using the above message structures to achieve the task of initiating TCP clients and sending data to them locally and remotely. In the case of Local Remote Port Forwards or SOCKS5 Proxies, the local messenger client would be the Messenger Server. In the case of Remote Port Forwards, the local messenger client would be the Messenger Client.

General Connection Request and Data Propagation Negotiation

sequenceDiagram
    autonumber
    participant LTCP as Local TCP Client
    participant LMC as Local Messenger Client
    participant RMC as Remote Messenger Client
    participant RTCP as Remote TCP Client

    LTCP ->> LMC: Connect
    LMC ->> RMC: Send InitiateForwarderClientReq
    Note right of LMC: Enqueue Message if Messenger Client is Stateless or Disconnected.
    RMC ->> RTCP: Connect
    RMC ->> LMC: InitiateForwarderClientRep
    Note left of RMC: Reason field is set to a non-zero value if unsuccessful, otherwise zero. 
    LMC ->> LTCP: Receive data
    Note left of LMC: Receive if reason is zero, otherwise disconnect and remove Forwarder Client.
    LMC ->> RMC: Send SendData
    Note right of LMC: Enqueue Message if Messenger Client is Stateless or Disconnected.
    RMC ->> RTCP: Send data
    RMC ->> RTCP: Receive Data
    Note right of RMC: Receive if client connected, otherwise send empty SendData and delete Forwarder Client. 
    RMC ->> LMC: Send SendData
    Note right of LMC: Enqueue Message if Messenger Client is Stateless or Disconnected.
    LMC ->> LTCP: Send data
    Note left of LMC: Send if data exists otherwise, disconnect the socket and delete the Forwarder Client.
    LMC ->> LTCP: Receive data
    Note left of LMC: Repeat process from step 5 until disconnected, then send empty SendData and delete Forwarder Client.
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