92 lines
3.2 KiB
Markdown
92 lines
3.2 KiB
Markdown
write-file-atomic
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-----------------
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This is an extension for node's `fs.writeFile` that makes its operation
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atomic and allows you set ownership (uid/gid of the file).
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### `writeFileAtomic(filename, data, [options], [callback])`
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#### Description:
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Atomically and asynchronously writes data to a file, replacing the file if it already
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exists. data can be a string or a buffer.
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#### Options:
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* filename **String**
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* data **String** | **Buffer**
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* options **Object** | **String**
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* chown **Object** default, uid & gid of existing file, if any
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* uid **Number**
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* gid **Number**
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* encoding **String** | **Null** default = 'utf8'
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* fsync **Boolean** default = true
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* mode **Number** default, from existing file, if any
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* tmpfileCreated **Function** called when the tmpfile is created
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* callback **Function**
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#### Usage:
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```js
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var writeFileAtomic = require('write-file-atomic')
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writeFileAtomic(filename, data, [options], [callback])
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```
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The file is initially named `filename + "." + murmurhex(__filename, process.pid, ++invocations)`.
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Note that `require('worker_threads').threadId` is used in addition to `process.pid` if running inside of a worker thread.
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If writeFile completes successfully then, if passed the **chown** option it will change
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the ownership of the file. Finally it renames the file back to the filename you specified. If
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it encounters errors at any of these steps it will attempt to unlink the temporary file and then
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pass the error back to the caller.
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If multiple writes are concurrently issued to the same file, the write operations are put into a queue and serialized in the order they were called, using Promises. Writes to different files are still executed in parallel.
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If provided, the **chown** option requires both **uid** and **gid** properties or else
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you'll get an error. If **chown** is not specified it will default to using
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the owner of the previous file. To prevent chown from being ran you can
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also pass `false`, in which case the file will be created with the current user's credentials.
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If **mode** is not specified, it will default to using the permissions from
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an existing file, if any. Expicitly setting this to `false` remove this default, resulting
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in a file created with the system default permissions.
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If options is a String, it's assumed to be the **encoding** option. The **encoding** option is ignored if **data** is a buffer. It defaults to 'utf8'.
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If the **fsync** option is **false**, writeFile will skip the final fsync call.
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If the **tmpfileCreated** option is specified it will be called with the name of the tmpfile when created.
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Example:
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```javascript
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writeFileAtomic('message.txt', 'Hello Node', {chown:{uid:100,gid:50}}, function (err) {
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if (err) throw err;
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console.log('It\'s saved!');
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});
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```
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This function also supports async/await:
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```javascript
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(async () => {
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try {
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await writeFileAtomic('message.txt', 'Hello Node', {chown:{uid:100,gid:50}});
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console.log('It\'s saved!');
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} catch (err) {
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console.error(err);
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process.exit(1);
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}
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})();
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```
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### `writeFileAtomicSync(filename, data, [options])`
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#### Description:
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The synchronous version of **writeFileAtomic**.
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#### Usage:
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```js
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var writeFileAtomicSync = require('write-file-atomic').sync
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writeFileAtomicSync(filename, data, [options])
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```
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