event-storage
Version:
An optimized embedded event store for node.js
49 lines (42 loc) • 1.31 kB
JavaScript
const ReadableIndex = require('./ReadableIndex');
const watchesFile = require('../WatchesFile');
/**
* A read-only index is a readable index instance that reacts on file changes and triggers events.
* If the underlying index was written to, an 'append' event is emitted, with the previous index length and the new index length.
* If the underlying index was truncated, a 'truncate' event is emitted, with the previous index length and the new index length.
*/
class ReadOnlyIndex extends watchesFile(ReadableIndex) {
/**
* @inheritDoc
*/
constructor(name, options) {
super(name, options);
}
/**
* @private
* @param {string} filename
*/
onChange(filename) {
/* istanbul ignore if */
if (!this.fd) {
return;
}
const prevLength = this.data.length;
const newLength = this.readFileLength();
this.data.length = newLength;
if (newLength > prevLength) {
this.emit('append', prevLength, newLength);
}
if (newLength < prevLength) {
this.emit('truncate', prevLength, newLength);
}
}
/**
* @private
* @param {string} filename
*/
onRename(filename) {
this.close();
}
}
module.exports = ReadOnlyIndex;