buffered-process.js

const _ = require('underscore-plus')
const ChildProcess = require('child_process')
const {Emitter} = require('event-kit')
const path = require('path')

// Extended: A wrapper which provides standard error/output line buffering for
// Node's ChildProcess.
//
// ## Examples
//
// ```js
// {BufferedProcess} = require('atom')
//
// const command = 'ps'
// const args = ['-ef']
// const stdout = (output) => console.log(output)
// const exit = (code) => console.log("ps -ef exited with #{code}")
// const process = new BufferedProcess({command, args, stdout, exit})
// ```
module.exports =
class BufferedProcess {
  /*
  Section: Construction
  */

  // Public: Runs the given command by spawning a new child process.
  //
  // * `options` An {Object} with the following keys:
  //   * `command` The {String} command to execute.
  //   * `args` The {Array} of arguments to pass to the command (optional).
  //   * `options` {Object} (optional) The options {Object} to pass to Node's
  //     `ChildProcess.spawn` method.
  //   * `stdout` {Function} (optional) The callback that receives a single
  //     argument which contains the standard output from the command. The
  //     callback is called as data is received but it's buffered to ensure only
  //     complete lines are passed until the source stream closes. After the
  //     source stream has closed all remaining data is sent in a final call.
  //     * `data` {String}
  //   * `stderr` {Function} (optional) The callback that receives a single
  //     argument which contains the standard error output from the command. The
  //     callback is called as data is received but it's buffered to ensure only
  //     complete lines are passed until the source stream closes. After the
  //     source stream has closed all remaining data is sent in a final call.
  //     * `data` {String}
  //   * `exit` {Function} (optional) The callback which receives a single
  //     argument containing the exit status.
  //     * `code` {Number}
  //   * `autoStart` {Boolean} (optional) Whether the command will automatically start
  //     when this BufferedProcess is created. Defaults to true.  When set to false you
  //     must call the `start` method to start the process.
  constructor ({command, args, options = {}, stdout, stderr, exit, autoStart = true} = {}) {
    this.emitter = new Emitter()
    this.command = command
    this.args = args
    this.options = options
    this.stdout = stdout
    this.stderr = stderr
    this.exit = exit
    if (autoStart === true) {
      this.start()
    }
    this.killed = false
  }

  start () {
    if (this.started === true) return

    this.started = true
    // Related to joyent/node#2318
    if (process.platform === 'win32' && this.options.shell === undefined) {
      this.spawnWithEscapedWindowsArgs(this.command, this.args, this.options)
    } else {
      this.spawn(this.command, this.args, this.options)
    }
    this.handleEvents(this.stdout, this.stderr, this.exit)
  }

  // Windows has a bunch of special rules that node still doesn't take care of for you
  spawnWithEscapedWindowsArgs (command, args, options) {
    let cmdArgs = []
    // Quote all arguments and escapes inner quotes
    if (args) {
      cmdArgs = args.filter((arg) => arg != null)
        .map((arg) => {
          if (this.isExplorerCommand(command) && /^\/[a-zA-Z]+,.*$/.test(arg)) {
            // Don't wrap /root,C:\folder style arguments to explorer calls in
            // quotes since they will not be interpreted correctly if they are
            return arg
          } else {
            // Escape double quotes by putting a backslash in front of them
            return `\"${arg.toString().replace(/"/g, '\\"')}\"`
          }
        })
    }

    // The command itself is quoted if it contains spaces, &, ^, | or # chars
    cmdArgs.unshift(/\s|&|\^|\(|\)|\||#/.test(command) ? `\"${command}\"` : command)

    const cmdOptions = _.clone(options)
    cmdOptions.windowsVerbatimArguments = true

    this.spawn(this.getCmdPath(), ['/s', '/d', '/c', `\"${cmdArgs.join(' ')}\"`], cmdOptions)
  }

  /*
  Section: Event Subscription
  */

  // Public: Will call your callback when an error will be raised by the process.
  // Usually this is due to the command not being available or not on the PATH.
  // You can call `handle()` on the object passed to your callback to indicate
  // that you have handled this error.
  //
  // * `callback` {Function} callback
  //   * `errorObject` {Object}
  //     * `error` {Object} the error object
  //     * `handle` {Function} call this to indicate you have handled the error.
  //       The error will not be thrown if this function is called.
  //
  // Returns a {Disposable}
  onWillThrowError (callback) {
    return this.emitter.on('will-throw-error', callback)
  }

  /*
  Section: Helper Methods
  */

  // Helper method to pass data line by line.
  //
  // * `stream` The Stream to read from.
  // * `onLines` The callback to call with each line of data.
  // * `onDone` The callback to call when the stream has closed.
  bufferStream (stream, onLines, onDone) {
    stream.setEncoding('utf8')
    let buffered = ''

    stream.on('data', (data) => {
      if (this.killed) return

      let bufferedLength = buffered.length
      buffered += data
      let lastNewlineIndex = data.lastIndexOf('\n')

      if (lastNewlineIndex !== -1) {
        let lineLength = lastNewlineIndex + bufferedLength + 1
        onLines(buffered.substring(0, lineLength))
        buffered = buffered.substring(lineLength)
      }
    })

    stream.on('close', () => {
      if (this.killed) return
      if (buffered.length > 0) onLines(buffered)
      onDone()
    })
  }

  // Kill all child processes of the spawned cmd.exe process on Windows.
  //
  // This is required since killing the cmd.exe does not terminate child
  // processes.
  killOnWindows () {
    if (!this.process) return

    const parentPid = this.process.pid
    const cmd = 'wmic'
    const args = [
      'process',
      'where',
      `(ParentProcessId=${parentPid})`,
      'get',
      'processid'
    ]

    let wmicProcess

    try {
      wmicProcess = ChildProcess.spawn(cmd, args)
    } catch (spawnError) {
      this.killProcess()
      return
    }

    wmicProcess.on('error', () => {}) // ignore errors

    let output = ''
    wmicProcess.stdout.on('data', (data) => {
      output += data
    })
    wmicProcess.stdout.on('close', () => {
      for (let pid of output.split(/\s+/)) {
        if (!/^\d{1,10}$/.test(pid)) continue
        pid = parseInt(pid, 10)

        if (!pid || pid === parentPid) continue

        try {
          process.kill(pid)
        } catch (error) {}
      }

      this.killProcess()
    })
  }

  killProcess () {
    if (this.process) this.process.kill()
    this.process = null
  }

  isExplorerCommand (command) {
    if (command === 'explorer.exe' || command === 'explorer') {
      return true
    } else if (process.env.SystemRoot) {
      return command === path.join(process.env.SystemRoot, 'explorer.exe') || command === path.join(process.env.SystemRoot, 'explorer')
    } else {
      return false
    }
  }

  getCmdPath () {
    if (process.env.comspec) {
      return process.env.comspec
    } else if (process.env.SystemRoot) {
      return path.join(process.env.SystemRoot, 'System32', 'cmd.exe')
    } else {
      return 'cmd.exe'
    }
  }

  // Public: Terminate the process.
  kill () {
    if (this.killed) return

    this.killed = true
    if (process.platform === 'win32') {
      this.killOnWindows()
    } else {
      this.killProcess()
    }
  }

  spawn (command, args, options) {
    try {
      this.process = ChildProcess.spawn(command, args, options)
    } catch (spawnError) {
      process.nextTick(() => this.handleError(spawnError))
    }
  }

  handleEvents (stdout, stderr, exit) {
    if (!this.process) return

    const triggerExitCallback = () => {
      if (this.killed) return
      if (stdoutClosed && stderrClosed && processExited && typeof exit === 'function') {
        exit(exitCode)
      }
    }

    let stdoutClosed = true
    let stderrClosed = true
    let processExited = true
    let exitCode = 0

    if (stdout) {
      stdoutClosed = false
      this.bufferStream(this.process.stdout, stdout, () => {
        stdoutClosed = true
        triggerExitCallback()
      })
    }

    if (stderr) {
      stderrClosed = false
      this.bufferStream(this.process.stderr, stderr, () => {
        stderrClosed = true
        triggerExitCallback()
      })
    }

    if (exit) {
      processExited = false
      this.process.on('exit', (code) => {
        exitCode = code
        processExited = true
        triggerExitCallback()
      })
    }

    this.process.on('error', (error) => {
      this.handleError(error)
    })
  }

  handleError (error) {
    let handled = false

    const handle = () => {
      handled = true
    }

    this.emitter.emit('will-throw-error', {error, handle})

    if (error.code === 'ENOENT' && error.syscall.indexOf('spawn') === 0) {
      error = new Error(`Failed to spawn command \`${this.command}\`. Make sure \`${this.command}\` is installed and on your PATH`, error.path)
      error.name = 'BufferedProcessError'
    }

    if (!handled) throw error
  }
}