Add event stream

[benbjohnson]

This pull request implements the GET /events endpoint which provides a newline-delimited stream of JSON objects. Currently, it implements 3 types of events: init, tx, & primaryChange.

/cc @tantaman

TODO

• Add unit tests
• Add documentation (LiteFS event stream docs docs#968)

Event Types

init

The init event is currently identical to the primaryChange event in that it shows information about this primary status. It is always the first event published.

{
    "type": "init",
    "data":
    {
        "isPrimary": true,
        "hostname": "myPrimaryHost"
    }
}

tx

The tx event is published every time a new LTX is written by the node or is received and applied from the primary.

{
    "type": "tx",
    "db": "db",
    "data":
    {
        "txID": "0000000000000027",
        "postApplyChecksum": "83b05248774ce767",
        "pageSize": 4096,
        "commit": 2,
        "timestamp": "2023-09-06T19:12:34.985Z"
    }
}

primaryChange

The primaryChange event shows information about this primary status. It is delivered when the node becomes primary, loses primary status, connects to a primary, or loses its connection to the primary.

{
    "type": "init",
    "data":
    {
        "isPrimary": true,
        "hostname": "myPrimaryHost"
    }
}

Usage

$ curl localhost:20202/events
{"type":"init","data":{"isPrimary":true}}
{"type":"tx","db":"db","data":{"txID":"0000000000000027","postApplyChecksum":"83b05248774ce767","pageSize":4096,"commit":2,"timestamp":"2023-09-06T19:12:34.985Z"}}
{"type":"tx","db":"db","data":{"txID":"0000000000000028","postApplyChecksum":"8467267f644a1b66","pageSize":4096,"commit":2,"timestamp":"2023-09-06T19:12:39.586Z"}}