write-file-atomic

write-file-atomic
-----------------

This is an extension for node's fs.writeFile that makes its operation
atomic and allows you set ownership (uid/gid of the file).

$3

#### Description:

Atomically and asynchronously writes data to a file, replacing the file if it already
exists. data can be a string or a buffer.

#### Options:
* filename String
* data String | Buffer
* options Object | String
* chown Object default, uid & gid of existing file, if any
* uid Number
* gid Number
* encoding String | Null default = 'utf8'
* fsync Boolean default = true
* mode Number default, from existing file, if any
* tmpfileCreated Function called when the tmpfile is created
* callback Function

#### Usage:

``js
var writeFileAtomic = require('write-file-atomic')
writeFileAtomic(filename, data, [options], [callback])
`

The file is initially named filename + "." + murmurhex(__filename, process.pid, ++invocations).
Note that require('worker_threads').threadId is used in addition to process.pid if running inside of a worker thread.
If writeFile completes successfully then, if passed the chown option it will change
the ownership of the file. Finally it renames the file back to the filename you specified. If
it encounters errors at any of these steps it will attempt to unlink the temporary file and then
pass the error back to the caller.
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.

If provided, the chown option requires both uid and gid properties or else
you'll get an error. If chown is not specified it will default to using
the owner of the previous file. To prevent chown from being ran you can
also pass false, in which case the file will be created with the current user's credentials.

If mode is not specified, it will default to using the permissions from
an existing file, if any. Expicitly setting this to false remove this default, resulting
in a file created with the system default permissions.

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'.

If the fsync option is false, writeFile will skip the final fsync call.

If the tmpfileCreated option is specified it will be called with the name of the tmpfile when created.

Example:

`javascript
writeFileAtomic('message.txt', 'Hello Node', {chown:{uid:100,gid:50}}, function (err) {
if (err) throw err;
console.log('It\'s saved!');
});
`

This function also supports async/await:

`javascript
(async () => {
try {
await writeFileAtomic('message.txt', 'Hello Node', {chown:{uid:100,gid:50}});
console.log('It\'s saved!');
} catch (err) {
console.error(err);
process.exit(1);
}
})();
`

$3

#### Description:

The synchronous version of writeFileAtomic.

#### Usage:
`js
var writeFileAtomicSync = require('write-file-atomic').sync
writeFileAtomicSync(filename, data, [options])
``