This memo provides information about how to implement a Websocket based communication between two devices as “extension” of the serial connection between an OOBD app and a dongle. Distribution of this memo is unlimited.

Copyright (C) OOBD Team (2014). All Rights Reserved.

The Name Kadaver comes from the german wording “Kabellose Daten- Verbindung” (Wireless Data Connection). It connects a OOBD app with a Dongle over the internet and let them talk to each other with a chat server in between

The connection from the App (called “Master”) and from the dongle (“Slave”) is made by Websocket connections (from now on simply called “the connection”). Both sides connect them self to that server, and the server then sends the communication back and forward.

The slave only provides the connection, so it shall be as simple as possible to be easily used by novice.

Both master and slave sending JSON messages to the server. The messages contain two properties:

• msg (Master) / receive (Slave): This is the text send to/from the dongle, coded in base64 (String)
• channel: The name of the channel with master and slave are both using (String)

The communication is initiated by the slave. The slave defines a name for the channel to use. This name can be random or e.g. the name of the Dongle, but it need to be unique for the time of the communication.

The slave then sends the above mentioned message to the server with this new channel name in channel and any value in reply. When reading the channel name out of the received JSON message, the Server assigns the channel to that websocket link.

Then the master needs to be informed about the channel name.

When then the master send it first message with that channel in channel and the dongle command in msg, then two things happen:

• the server assigns the channel name to the websocket link of the master
• the server then forwards the JSON message to the other clients with the same channel name (the slave)

After initialize the connection path, it's simple: Every message, which comes from one side is forwarded to the other and vice versa, identified by the channel name.

As this connectivity might be implemented on different platforms, the following requirements shall be seen to be mandatory to have a common look & feel and functionality

1. the Websocket Server URL shall be configurable and saveable in the settings
2. The user shall decide when doing the connection if he wants to do a local or remote connection
3. When doing the remote connection, he shall be able to enter the channel (which comes, as said, from the slave)

<graphviz dot> digraph finite_state_machine {

node [shape = box];
      n3  [ label = "(1)\nConnect to Webserver" ];
      n4  [ label = "(1a)\nDisplay Server settings\nfor correction & Retry" ];
      n5  [ label = "(2)\nCheck Bluetooth\nSocket Availability" ];
      n6  [ label = "(2a)\nInform User & Retry" ];
      n7  [ label = "(3)\nDo Bluetooth\nDongle Discovery\nNr. of Dongles found" ];
      n9  [ label = "(3a)\nInform User & Retry" ];
      n11 [ label = "(3b)\nDongle selection & Retry" ];
      n12 [ label = "(4)\nParing Dongle" ];
      n13  [ label = "(4a)\nInform User & Retry" ];
      n15  [ label = "(5)\nDisplay Channel\nNormal Operation" ];
      n16  [ label = "(99)\nEnd (Close Window)" ];

      n3 -> n4   [ label = "Error"  ];
      n3 -> n5   [ label = "Ok" color ="green" ];
      n4 -> n3   [ label = "Retry" ];
      n4 -> n16  [ label = "End" ];
      
      n5 -> n6   [ label = "Error" ];
      n5 -> n7   [ label = "Ok" color ="green" ];
      n6 -> n5   [ label = "Retry" ];
      n6 -> n16  [ label = "End" ];

      n7 -> n9 [ label = "0" ];
      
      n9 -> n7   [ label = "Retry" ];
      n9 -> n16  [ label = "End" ];
     
      n7 -> n11   [ label = ">1" ];
      n7 -> n12   [ label = "1" color ="green" ];
      n11 -> n12   [ label = "Pair" ];
      n11 -> n16  [ label = "End" ];

      n12 -> n13   [ label = "Error" ];
      n12 -> n15   [ label = "Ok" color ="green" ];
      n13 -> n12   [ label = "Retry" ];
      n13 -> n16  [ label = "End" ];
      
 

        n20  [ label = "User Settings" ];
        n21  [ label = "Webserver URL" ];
        n22  [ label = "Language" ];
   n20 -> n21 ; n20 -> n22 ;

} </graphviz>

to be defined

This RFC raises potential security issues. It's need to make sure that no issues can happen when somebody hijacks the data link

Steffen Koehler

Phone: +49 172 410 35 98

EMail:steffen@koehlers.de

Copyright (C) OOBD Team (2012). All Rights Reserved.

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