Append-only-log NPM

append-only-log

Abstract interface for an append-only log.

Like abstract-blob-store, but for append-only logs.

STATUS

Mad science work-in-progress! :dragon_face:

Usage

To use the test suite from this module, use require('append-only-log/tests').

You'll have to implement a setup and teardown function:

var common = {
  setup: function(t, cb) {
    // setup takes a tap/tape compatible test instance in and a callback
    // this method should construct a new blob store instance and pass it to the callback:
    var log = createMyLog()
    cb(null, log)
  },
  teardown: function(t, log, blob, cb) {
    // teardown takes in the test instance, as well as the log instance
    // you can use the log to clean up its data, e.g.
    if (log) {
      var stream = log.createReadStream()
      stream.on('data', function (entry) {
        entry.cleanup()
      })
      stream.on('end', cb)
    } else cb()
    // be sure to call cb() when you are done with teardown
  }
}

To run the tests simply pass your test module (tap or tape or any other compatible modules are supported) and your common methods in:

var appendOnlyLogTests = require('append-only-log/tests')
appendOnlyLogTests(test, common)

API

A valid append-only log should implement the following APIs. There is a reference in-memory implementation available at index.js in this repo.

log.append(value, cb)

Appends value to the end of the log. If a function cb is given, it will be called asynchronously as function (err, seq). seq is the sequence number of the appended entry.

log.get(seq, cb)

Gets the value with sequence number seq from the log asynchronously. cb has the signature function (err, value).

log.createReadStream(opts)

Returns a Readable stream of values in the append-only log, starting from the most recently appended. Some implementations may accept opts.reverse for reversed entries, but this is not guaranteed.