Recorder

  • The recorder works by recording incoming, outgoing messages, the times at which nodes connected/disconnected, times at which itself stopped and started.
  • Each node has 2 recorders, one for each stack. The recorder has a key value database which has the time as the key and value as the message.
  • The message has a marker indicating the type of the message. The recorder has a can be queried to return messages in the order and with correct time apart between them. eg. if node had 3 messages at 15 sec, 20 sec and 25 sec, the recorder’s get_next method will return the first message the first time is called but it will not return the next message until 5 seconds have passed; it does not block, but just returns None.
  • The recorder records messages coming into verifyAndAppend for each stack.
  • During the replay, recorders are combined to for a CombinedRecorder is used for the replay.
  • Also during replay, the times of the Node are patched to match the actual time of the Node run.
  • Also the information about which PRE-PREPARE sent which requests at what time are extracted before the replay starts so that during the replay the node sends the same PRE-PREPARES.
  • During the replay the node, stops at appropriate intervals at which the original node stopped.
  • Also the node calls simulates disconnections from other nodes at the appropriate time.
  • During the replay the node sends no outgoing messages neither does it have the recorder attached.
  • The replay is supposed to be run as a standalone node, most probably in an IDE so it can be debugged.
  • The record and and replay functionality is controlled through the config flag STACK_COMPANION. It has 3 possible values
    • 0 for normal operation
    • 1 for recorder
    • 2 during replay
  • The node is run with the STACK_COMPANION set to 1 and the recorder directory is created under data/<node name>. This directory is either copied or a script in indy-node is used to copy the directories. The directories are given to the developer who uses a script in indy-node to replay.