87 lines
2.0 KiB
Markdown
87 lines
2.0 KiB
Markdown
safe-replace
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============
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A micro-module for safely replacing a file.
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This is intended to be generally safe even when a function that writes a file
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is accidentally called twice (as may happen with node cluster).
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Commandline Reference
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---------------------
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If I want to safely replace a file with a new version, I would do so like this:
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```bash
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# create the new version
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touch keep.txt.RANDOM.tmp
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# remove the previous backup
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rm -f keep.txt.bak
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# move the current version to the backup
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mv keep.txt keep.txt.bak
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# move the new version to the current
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mv keep.txt.RANDOM.tmp keep.txt
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```
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If `keep.txt` became corrupt and I wanted to use the backup,
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I would do this:
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```bash
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# copy the backup to the new version
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rsync keep.txt.bak keep.txt
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```
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In Node
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-------
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I ported that proccess to node.
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```
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sfs.writeFileAsync
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sfs.stageAsync
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sfs.commitAsync
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sfs.revertAsync
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```
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```js
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// default behavior is to concat (filename + '.' + rnd() + '.tmp')
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var safeReplace = require('safe-replace').create({ tmp: 'tmp', bak: 'bak' });
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var data = new Buffer('A priceless document');
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safeReplace.writeFileAsync('keep.txt', data, 'ascii').then(function () {
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fs.readdir('.', function (nodes) {
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console.log('file system nodes', nodes);
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// keep.txt
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// keep.txt.bak
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});
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});
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// let's say I want to write a tmp file and not commit it... weird
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safeReplace.stageAsync('keep.txt', data, 'ascii').then(function (tmpname) {
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fs.readdir('.', function (nodes) {
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console.log('file system nodes', nodes);
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// keep.txt.ac71teh8mja.tmp
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});
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});
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// let's say I wrote keep.txt.x7t7sq926.tmp with my own mechanism
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safeReplace.commitAsync('keep.txt.x7t7sq926.tmp', 'keep.txt').then(function () {
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fs.readdir('.', function (nodes) {
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console.log('file system nodes', nodes);
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// keep.txt
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// keep.txt.bak
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});
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});
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// let's say I want to revert the file from the '.bak'
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safeReplace.revertAsync('keep.txt').then(function () {
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fs.readdir('.', function (nodes) {
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console.log('file system nodes', nodes);
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// keep.txt
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// keep.txt.bak
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});
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});
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```
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