level-change-processor

Follows a changes-feed and processes each entry, storing state in a levelup. Automatically handles resuming the changes processing from where it left off when restarted.

Designed for creating secondary indexes with leveldb but can be used in many different applications.

Usage

require('level-change-processor')(opts)

Construct a new change processor instance.

opts is an object:

• db (required) - a levelup to store the change state in
• feed (required) - a changes-feed instance
• worker (required) - a function (see below) that processes each change
• key (default latest) - a key to use to store the change state in the db above
• dbOptions (default {valueEncoding: 'utf8'}) - options to pass to the db .get and .put calls

example:

var processor = changeProcessor({
  db: stateDb,
  feed: feed,
  worker: worker
})

Worker function

A function that takes two arguments: (change, cb).

change will be an object with these properties:

• change - this will be a js Number that increments by 1 for every change, starting at 1
• value - this will be the change payload that the changes feed writes to you. usually is a Buffer but depends on the feed

These are the two guaranteed properties. There may be other properties on change depending on the feed.

error handling

To catch errors attach a processor.on('error', errorHandler) event