index.js

'use strict'
module.exports = writeFile
module.exports.sync = writeFileSync
module.exports._getTmpname = getTmpname // for testing
module.exports._cleanupOnExit = cleanupOnExit

const fs = require('fs')
const MurmurHash3 = require('imurmurhash')
const { onExit } = require('signal-exit')
const path = require('path')
const { promisify } = require('util')
const activeFiles = {}

// if we run inside of a worker_thread, `process.pid` is not unique
/* istanbul ignore next */
const threadId = (function getId () {
  try {
    const workerThreads = require('worker_threads')

    /// if we are in main thread, this is set to `0`
    return workerThreads.threadId
  } catch (e) {
    // worker_threads are not available, fallback to 0
    return 0
  }
})()

let invocations = 0
function getTmpname (filename) {
  return filename + '.' +
    MurmurHash3(__filename)
      .hash(String(process.pid))
      .hash(String(threadId))
      .hash(String(++invocations))
      .result()
}

function cleanupOnExit (tmpfile) {
  return () => {
    try {
      fs.unlinkSync(typeof tmpfile === 'function' ? tmpfile() : tmpfile)
    } catch {
      // ignore errors
    }
  }
}

function serializeActiveFile (absoluteName) {
  return new Promise(resolve => {
    // make a queue if it doesn't already exist
    if (!activeFiles[absoluteName]) {
      activeFiles[absoluteName] = []
    }

    activeFiles[absoluteName].push(resolve) // add this job to the queue
    if (activeFiles[absoluteName].length === 1) {
      resolve()
    } // kick off the first one
  })
}

// https://github.com/isaacs/node-graceful-fs/blob/master/polyfills.js#L315-L342
function isChownErrOk (err) {
  if (err.code === 'ENOSYS') {
    return true
  }

  const nonroot = !process.getuid || process.getuid() !== 0
  if (nonroot) {
    if (err.code === 'EINVAL' || err.code === 'EPERM') {
      return true
    }
  }

  return false
}

async function writeFileAsync (filename, data, options = {}) {
  if (typeof options === 'string') {
    options = { encoding: options }
  }

  let fd
  let tmpfile
  /* istanbul ignore next -- The closure only gets called when onExit triggers */
  const removeOnExitHandler = onExit(cleanupOnExit(() => tmpfile))
  const absoluteName = path.resolve(filename)

  try {
    await serializeActiveFile(absoluteName)
    const truename = await promisify(fs.realpath)(filename).catch(() => filename)
    tmpfile = getTmpname(truename)

    if (!options.mode || !options.chown) {
      // Either mode or chown is not explicitly set
      // Default behavior is to copy it from original file
      const stats = await promisify(fs.stat)(truename).catch(() => {})
      if (stats) {
        if (options.mode == null) {
          options.mode = stats.mode
        }

        if (options.chown == null && process.getuid) {
          options.chown = { uid: stats.uid, gid: stats.gid }
        }
      }
    }

    fd = await promisify(fs.open)(tmpfile, 'w', options.mode)
    if (options.tmpfileCreated) {
      await options.tmpfileCreated(tmpfile)
    }
    if (ArrayBuffer.isView(data)) {
      await promisify(fs.write)(fd, data, 0, data.length, 0)
    } else if (data != null) {
      await promisify(fs.write)(fd, String(data), 0, String(options.encoding || 'utf8'))
    }

    if (options.fsync !== false) {
      await promisify(fs.fsync)(fd)
    }

    await promisify(fs.close)(fd)
    fd = null

    if (options.chown) {
      await promisify(fs.chown)(tmpfile, options.chown.uid, options.chown.gid).catch(err => {
        if (!isChownErrOk(err)) {
          throw err
        }
      })
    }

    if (options.mode) {
      await promisify(fs.chmod)(tmpfile, options.mode).catch(err => {
        if (!isChownErrOk(err)) {
          throw err
        }
      })
    }

    await promisify(fs.rename)(tmpfile, truename)
  } finally {
    if (fd) {
      await promisify(fs.close)(fd).catch(
        /* istanbul ignore next */
        () => {}
      )
    }
    removeOnExitHandler()
    await promisify(fs.unlink)(tmpfile).catch(() => {})
    activeFiles[absoluteName].shift() // remove the element added by serializeSameFile
    if (activeFiles[absoluteName].length > 0) {
      activeFiles[absoluteName][0]() // start next job if one is pending
    } else {
      delete activeFiles[absoluteName]
    }
  }
}

async function writeFile (filename, data, options, callback) {
  if (options instanceof Function) {
    callback = options
    options = {}
  }

  const promise = writeFileAsync(filename, data, options)
  if (callback) {
    try {
      const result = await promise
      return callback(result)
    } catch (err) {
      return callback(err)
    }
  }

  return promise
}

function writeFileSync (filename, data, options) {
  if (typeof options === 'string') {
    options = { encoding: options }
  } else if (!options) {
    options = {}
  }
  try {
    filename = fs.realpathSync(filename)
  } catch (ex) {
    // it's ok, it'll happen on a not yet existing file
  }
  const tmpfile = getTmpname(filename)

  if (!options.mode || !options.chown) {
    // Either mode or chown is not explicitly set
    // Default behavior is to copy it from original file
    try {
      const stats = fs.statSync(filename)
      options = Object.assign({}, options)
      if (!options.mode) {
        options.mode = stats.mode
      }
      if (!options.chown && process.getuid) {
        options.chown = { uid: stats.uid, gid: stats.gid }
      }
    } catch (ex) {
      // ignore stat errors
    }
  }

  let fd
  const cleanup = cleanupOnExit(tmpfile)
  const removeOnExitHandler = onExit(cleanup)

  let threw = true
  try {
    fd = fs.openSync(tmpfile, 'w', options.mode || 0o666)
    if (options.tmpfileCreated) {
      options.tmpfileCreated(tmpfile)
    }
    if (ArrayBuffer.isView(data)) {
      fs.writeSync(fd, data, 0, data.length, 0)
    } else if (data != null) {
      fs.writeSync(fd, String(data), 0, String(options.encoding || 'utf8'))
    }
    if (options.fsync !== false) {
      fs.fsyncSync(fd)
    }

    fs.closeSync(fd)
    fd = null

    if (options.chown) {
      try {
        fs.chownSync(tmpfile, options.chown.uid, options.chown.gid)
      } catch (err) {
        if (!isChownErrOk(err)) {
          throw err
        }
      }
    }

    if (options.mode) {
      try {
        fs.chmodSync(tmpfile, options.mode)
      } catch (err) {
        if (!isChownErrOk(err)) {
          throw err
        }
      }
    }

    fs.renameSync(tmpfile, filename)
    threw = false
  } finally {
    if (fd) {
      try {
        fs.closeSync(fd)
      } catch (ex) {
        // ignore close errors at this stage, error may have closed fd already.
      }
    }
    removeOnExitHandler()
    if (threw) {
      cleanup()
    }
  }
}