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116 lines
3.3 KiB
116 lines
3.3 KiB
/**
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* Way data is stored for this database
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* For a Node.js/Node Webkit database it's the file system
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* For a browser-side database it's localforage which chooses the best option depending on user browser (IndexedDB then WebSQL then localStorage)
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*
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* This version is the Node.js/Node Webkit version
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* It's essentially fs, mkdirp and crash safe write and read functions
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*/
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var fs = require('fs')
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, mkdirp = require('mkdirp')
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, async = require('async')
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, storage = {}
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;
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storage.exists = fs.exists;
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storage.rename = fs.rename;
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storage.writeFile = fs.writeFile;
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storage.unlink = fs.unlink;
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storage.appendFile = fs.appendFile;
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storage.readFile = fs.readFile;
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storage.mkdirp = mkdirp;
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/**
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* Explicit name ...
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*/
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storage.ensureFileDoesntExist = function (file, callback) {
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storage.exists(file, function (exists) {
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if (!exists) { return callback(null); }
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storage.unlink(file, function (err) { return callback(err); });
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});
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};
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/**
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* Flush data in OS buffer to storage if corresponding option is set
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*/
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storage.flushToStorage = function (filename, callback) {
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fs.open(filename, 'r', function (err, fd) {
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if (err) { return callback(err); }
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fs.fsync(fd, function (err) { return callback(err); });
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});
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};
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/**
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* Fully write or rewrite the datafile, immune to crashes during the write operation (data will not be lost)
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* @param {String} filename
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* @param {String} data
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* @param {Function} cb Optional callback, signature: err
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*/
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storage.crashSafeWriteFile = function (filename, data, cb) {
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var callback = cb || function () {}
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, tempFilename = filename + '~'
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, oldFilename = filename + '~~'
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;
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async.waterfall([
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async.apply(storage.ensureFileDoesntExist, tempFilename)
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, async.apply(storage.ensureFileDoesntExist, oldFilename)
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, function (cb) {
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storage.exists(filename, function (exists) {
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if (exists) {
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storage.rename(filename, oldFilename, function (err) {
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if (err) { return cb(err); }
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storage.flushToStorage(oldFilename, cb); // Ensure filename doesn't exist due to rename atomicity
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});
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} else {
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return cb();
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}
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});
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}
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, function (cb) {
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storage.writeFile(tempFilename, data, function (err) { return cb(err); });
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}
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, function (cb) {
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storage.rename(tempFilename, filename, function (err) { return cb(err); });
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}
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, async.apply(storage.flushToStorage, filename)
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, async.apply(storage.ensureFileDoesntExist, oldFilename)
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], function (err) { return callback(err); })
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};
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/**
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* Ensure the datafile contains all the data, even if there was a crash during a full file write
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* @param {String} filename
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* @param {Function} callback signature: err
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*/
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storage.ensureDatafileIntegrity = function (filename, callback) {
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var tempFilename = filename + '~'
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, oldFilename = filename + '~~'
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;
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storage.exists(filename, function (filenameExists) {
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// Write was successful
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if (filenameExists) { return callback(null); }
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storage.exists(oldFilename, function (oldFilenameExists) {
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// New database
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if (!oldFilenameExists) {
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return storage.writeFile(filename, '', 'utf8', function (err) { callback(err); });
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}
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// Write failed, use old version
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storage.rename(oldFilename, filename, function (err) { return callback(err); });
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});
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});
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};
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// Interface
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module.exports = storage;
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