etcher/lib/child-writer/index.js

/*
 * Copyright 2016 resin.io
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

'use strict';

const EventEmitter = require('events').EventEmitter;
const _ = require('lodash');
const childProcess = require('child_process');
const ipc = require('node-ipc');
const rendererUtils = require('./renderer-utils');
const cli = require('./cli');
const CONSTANTS = require('./constants');
const EXIT_CODES = require('../shared/exit-codes');
const robot = require('../shared/robot');

/**
 * @summary Perform a write
 * @function
 * @public
 *
 * @param {String} image - image
 * @param {Object} drive - drive
 * @param {Object} options - options
 * @returns {EventEmitter} event emitter
 *
 * @example
 * const child = childWriter.write('path/to/rpi.img', {
 *   device: '/dev/disk2'
 * }, {
 *   validateWriteOnSuccess: true,
 *   unmountOnSuccess: true
 * });
 *
 * child.on('progress', (state) => {
 *   console.log(state);
 * });
 *
 * child.on('error', (error) => {
 *   throw error;
 * });
 *
 * child.on('done', () => {
 *   console.log('Validation was successful!');
 * });
 */
exports.write = (image, drive, options) => {
  const emitter = new EventEmitter();

  const argv = cli.getArguments({
    entryPoint: rendererUtils.getApplicationEntryPoint(),
    image,
    device: drive.device,
    validateWriteOnSuccess: options.validateWriteOnSuccess,
    unmountOnSuccess: options.unmountOnSuccess
  });

  // There might be multiple Etcher instances running at
  // the same time, therefore we must ensure each IPC
  // server/client has a different name.
  process.env.IPC_SERVER_ID = `etcher-server-${process.pid}`;
  process.env.IPC_CLIENT_ID = `etcher-client-${process.pid}`;

  ipc.config.id = process.env.IPC_SERVER_ID;
  ipc.config.silent = true;
  ipc.serve();

  /**
   * @summary Safely terminate the IPC server
   * @function
   * @private
   *
   * @example
   * terminateServer();
   */
  const terminateServer = () => {

    // Turns out we need to destroy all sockets for
    // the server to actually close. Otherwise, it
    // just stops receiving any further connections,
    // but remains open if there are active ones.
    _.each(ipc.server.sockets, (socket) => {
      socket.destroy();
    });

    ipc.server.stop();
  };

  /**
   * @summary Emit an error to the client
   * @function
   * @private
   *
   * @param {Error} error - error
   *
   * @example
   * emitError(new Error('foo bar'));
   */
  const emitError = (error) => {
    terminateServer();
    emitter.emit('error', error);
  };

  /**
   * @summary Bridge robot message to the child writer caller
   * @function
   * @private
   *
   * @param {String} message - robot message
   *
   * @example
   * bridgeRobotMessage(robot.buildMessage('foo', {
   *   bar: 'baz'
   * }));
   */
  const bridgeRobotMessage = (message) => {
    try {
      const parsedMessage = robot.parseMessage(message);

      // These are lighweight accessor methods for
      // the properties of the parsed message
      const messageCommand = robot.getCommand(parsedMessage);
      const messageData = robot.getData(parsedMessage);

      // The error object is decomposed by the CLI for serialisation
      // purposes. We compose it back to an `Error` here in order
      // to provide better encapsulation.
      if (messageCommand === 'error') {
        emitError(robot.recomposeErrorMessage(parsedMessage));
      } else if (messageCommand === 'log') {
        console.log(messageData);
      } else {
        emitter.emit(messageCommand, messageData);
      }

    } catch (error) {
      emitError(error);
    }
  };

  ipc.server.on('error', emitError);
  ipc.server.on('message', bridgeRobotMessage);

  ipc.server.on('start', () => {
    const child = childProcess.fork(CONSTANTS.WRITER_PROXY_SCRIPT, argv, {
      silent: true,
      env: process.env
    });

    child.stdout.on('data', (data) => {
      console.info(`WRITER: ${data.toString()}`);
    });

    child.stderr.on('data', (data) => {
      bridgeRobotMessage(data.toString());

      // This function causes the `close` event to be emitted
      child.kill();

    });

    child.on('error', emitError);

    child.on('close', (code) => {
      terminateServer();

      if (code === EXIT_CODES.CANCELLED) {
        return emitter.emit('done', {
          cancelled: true
        });
      }

      // We shouldn't emit the `done` event manually here
      // since the writer process will take care of it.
      if (code === EXIT_CODES.SUCCESS || code === EXIT_CODES.VALIDATION_ERROR) {
        return null;
      }

      return emitError(new Error(`Child process exited with error code: ${code}`));
    });
  });

  ipc.server.start();

  return emitter;
};