write-file-atomic

What is write-file-atomic?

The write-file-atomic npm package is designed to write files to disk atomically, meaning that it ensures that the file contents are either fully written or not written at all, preventing partial writes that can occur in crash scenarios. It also allows for setting file mode and ownership atomically with the file write.

What are write-file-atomic's main functionalities?

Atomic file writing

This feature ensures that the file is either completely written or not written at all, which is useful for preventing data corruption during write operations.

const writeFileAtomic = require('write-file-atomic');
writeFileAtomic('message.txt', 'Hello, World!', function (err) {
  if (err) throw err;
  console.log('The file has been saved!');
});

Setting file mode

This feature allows the user to set the file mode (permissions) at the time of writing the file atomically.

const writeFileAtomic = require('write-file-atomic');
writeFileAtomic('message.txt', 'Hello, World!', { mode: 0o755 }, function (err) {
  if (err) throw err;
  console.log('The file has been saved with the specified mode!');
});

Setting file ownership

This feature allows the user to set the file ownership (user ID and group ID) atomically with the file write operation.

const writeFileAtomic = require('write-file-atomic');
writeFileAtomic('message.txt', 'Hello, World!', { chown: { uid: 1000, gid: 50 } }, function (err) {
  if (err) throw err;
  console.log('The file has been saved with the specified ownership!');
});

Other packages similar to write-file-atomic

fs-extra

fs-extra is a package that builds on the native fs module, providing additional methods and ensuring compatibility across different platforms. It includes methods for atomic file writing, but also offers a wide range of other file system operations, making it more extensive than write-file-atomic.

graceful-fs

graceful-fs is a drop-in replacement for the fs module that makes file system operations more robust by queuing them and retrying on failure. It does not specifically focus on atomic writes, but it enhances the overall reliability of file system interactions.

atomic-write

atomic-write is a minimalistic module that provides atomic file writing capabilities. It is similar to write-file-atomic but with a smaller feature set and API surface area, focusing solely on the atomicity of the write operation.

README

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).

writeFileAtomic(filename, data, [options], [callback])

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:

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:

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:

(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);
  }
})();

writeFileAtomicSync(filename, data, [options])

Description:

The synchronous version of writeFileAtomic.

Usage:

var writeFileAtomicSync = require('write-file-atomic').sync
writeFileAtomicSync(filename, data, [options])