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;
  }
};