feat(writer): Impl multi-writes in writer modules

Implement writing to multiple destinations simultaneously

Change-Type: minor
Changelog-Entry: Implement writing to multiple destinations simultaneously

lib/cli/etcher.js

@@ -16,11 +16,12 @@
 
 'use strict'
 
-const path = require('path')
+const _ = require('lodash')
 const Bluebird = require('bluebird')
 const visuals = require('resin-cli-visuals')
 const form = require('resin-cli-form')
-const writer = require('./writer')
+const bytes = require('pretty-bytes')
+const ImageWriter = require('../sdk/writer')
 const utils = require('./utils')
 const options = require('./options')
 const messages = require('../shared/messages')
@@ -28,6 +29,8 @@ const EXIT_CODES = require('../shared/exit-codes')
 const errors = require('../shared/errors')
 const permissions = require('../shared/permissions')
 
+/* eslint-disable no-magic-numbers */
+
 const ARGV_IMAGE_PATH_INDEX = 0
 const imagePath = options._[ARGV_IMAGE_PATH_INDEX]
 
@@ -59,7 +62,6 @@ permissions.isElevated().then((elevated) => {
       // otherwise the question will not be asked because
       // `false` is a defined value.
       yes: options.yes || null
-
     }
   })
 }).then((answers) => {
@@ -75,29 +77,79 @@ permissions.isElevated().then((elevated) => {
     check: new visuals.Progress('Validating')
   }
 
-  return writer.writeImage(imagePath, answers.drive, {
+  return new Bluebird((resolve, reject) => {
-    unmountOnSuccess: options.unmount,
+    /**
-    validateWriteOnSuccess: options.check
+     * @summary Progress update handler
-  }, (state) => {
+     * @param {Object} state - progress state
-    progressBars[state.type].update(state)
+     * @private
-  }).then((results) => {
+     * @example
-    return {
+     * writer.on('progress', onProgress)
-      imagePath,
+     */
-      flash: results
+    const onProgress = (state) => {
+      state.message = state.active > 1
+        ? `${bytes(state.totalSpeed)}/s total, ${bytes(state.speed)}/s avg`
+        : `${bytes(state.totalSpeed)}/s`
+
+      state.message = `${state.type === 'write' ? 'Flashing' : 'Validating'}: ${state.message}`
+
+      // Update progress bar
+      progressBars[state.type].update(state)
     }
+
+    const writer = new ImageWriter({
+      verify: options.check,
+      unmountOnSuccess: options.unmount,
+      checksumAlgorithms: options.check ? [ 'sha512' ] : []
+    })
+
+    /**
+     * @summary Error handler
+     * @param {Error} error - error
+     * @private
+     * @example
+     * writer.on('error', onError)
+     */
+    const onError = function (error) {
+      console.error(error)
+    }
+
+    /**
+     * @summary Finish handler
+     * @private
+     * @example
+     * writer.on('finish', onFinish)
+     */
+    const onFinish = function () {
+      resolve(Array.from(writer.destinations.values()))
+    }
+
+    writer.on('progress', onProgress)
+    writer.on('error', onError)
+    writer.on('finish', onFinish)
+
+    // NOTE: Drive can be (String|Array)
+    const destinations = [].concat(answers.drive)
+
+    writer.write(imagePath, destinations)
   })
 }).then((results) => {
-  return Bluebird.try(() => {
+  let exitCode = EXIT_CODES.SUCCESS
-    console.log(messages.info.flashComplete(path.basename(results.imagePath), results.flash.drive))
 
-    if (results.flash.checksum.md5) {
+  if (options.check) {
-      console.log(`Checksum: ${results.flash.checksum.md5}`)
+    console.log('')
-    }
+    console.log('Checksums:')
 
-    return Bluebird.resolve()
+    _.forEach(results, (result) => {
-  }).then(() => {
+      if (result.error) {
-    process.exit(EXIT_CODES.SUCCESS)
+        exitCode = EXIT_CODES.GENERAL_ERROR
-  })
+        console.log(`  - ${result.device.device}: ${result.error.message}`)
+      } else {
+        console.log(`  - ${result.device.device}: ${result.checksum.sha512}`)
+      }
+    })
+  }
+
+  process.exit(exitCode)
 }).catch((error) => {
   return Bluebird.try(() => {
     utils.printError(error)

lib/cli/writer.js

@@ -1,62 +0,0 @@
-/*
- * 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 Bluebird = require('bluebird')
-const ImageWriter = require('../sdk/writer')
-
-/**
- * @summary Write an image to a disk drive
- * @function
- * @public
- *
- * @param {String} imagePath - path to image
- * @param {String} drive - drive
- * @param {Object} options - options
- * @param {Boolean} [options.unmountOnSuccess=false] - unmount on success
- * @param {Boolean} [options.validateWriteOnSuccess=false] - validate write on success
- * @param {Function} onProgress - on progress callback (state)
- *
- * @fulfil {Boolean} - whether the operation was successful
- * @returns {Promise}
- *
- * @example
- * writer.writeImage('path/to/image.img', '/dev/disk2', {
- *   unmountOnSuccess: true,
- *   validateWriteOnSuccess: true
- * }, (state) => {
- *   console.log(state.percentage);
- * }).then(() => {
- *   console.log('Done!');
- * });
- */
-exports.writeImage = (imagePath, drive, options, onProgress) => {
-  const writer = new ImageWriter({
-    path: drive,
-    imagePath,
-    verify: options.validateWriteOnSuccess,
-    checksumAlgorithms: [ 'md5' ],
-    unmountOnSuccess: options.unmountOnSuccess
-  })
-
-  return new Bluebird((resolve, reject) => {
-    writer.flash()
-      .on('error', reject)
-      .on('progress', onProgress)
-      .on('finish', resolve)
-  })
-}

lib/gui/app/modules/image-writer.js

@@ -36,7 +36,7 @@ const packageJSON = require('../../../../package.json')
  * @type {Number}
  * @constant
  */
-const THREADS_PER_CPU = 4
+const THREADS_PER_CPU = 16
 
 /**
  * @summary Get application entry point
@@ -69,7 +69,7 @@ const getApplicationEntryPoint = () => {
  * This function is extracted for testing purposes.
  *
  * @param {String} image - image path
- * @param {Object} drive - drive
+ * @param {Array<Object>} drives - drives
  * @param {Function} onProgress - in progress callback (state)
  *
  * @fulfil {Object} - flash results
@@ -82,7 +82,7 @@ const getApplicationEntryPoint = () => {
  *   console.log(state.percentage)
  * })
  */
-exports.performWrite = (image, drive, onProgress) => {
+exports.performWrite = (image, drives, onProgress) => {
   // There might be multiple Etcher instances running at
   // the same time, therefore we must ensure each IPC
   // server/client has a different name.
@@ -135,6 +135,16 @@ exports.performWrite = (image, drive, onProgress) => {
 
     ipc.server.on('state', onProgress)
 
+    ipc.server.on('ready', (data, socket) => {
+      ipc.server.emit(socket, 'write', {
+        imagePath: image,
+        destinations: _.map(drives, [ 'device' ]),
+        validateWriteOnSuccess: settings.get('validateWriteOnSuccess'),
+        unmountOnSuccess: settings.get('unmountOnSuccess'),
+        checksumAlgorithms: [ 'sha512' ]
+      })
+    })
+
     const argv = _.attempt(() => {
       const entryPoint = getApplicationEntryPoint()
 
@@ -167,31 +177,24 @@ exports.performWrite = (image, drive, onProgress) => {
 
       permissions.elevateCommand(argv, {
         applicationName: packageJSON.displayName,
-        environment: {
+        environment: _.assign({}, process.env, {
           IPC_SERVER_ID,
           IPC_CLIENT_ID,
           IPC_SOCKET_ROOT: ipc.config.socketRoot,
           ELECTRON_RUN_AS_NODE: 1,
           UV_THREADPOOL_SIZE: os.cpus().length * THREADS_PER_CPU,
 
-          // Casting to Number nicely converts booleans to 0 or 1.
-          OPTION_VALIDATE: Number(settings.get('validateWriteOnSuccess')),
-          OPTION_UNMOUNT: Number(settings.get('unmountOnSuccess')),
-
-          OPTION_IMAGE: image,
-          OPTION_DEVICE: drive.device,
-
           // This environment variable prevents the AppImages
           // desktop integration script from presenting the
           // "installation" dialog
           SKIP: 1
-        }
+        })
       }).then((results) => {
         flashResults.cancelled = results.cancelled
         console.log('Flash results', flashResults)
 
         // This likely means the child died halfway through
-        if (!flashResults.cancelled && !flashResults.bytesWritten) {
+        if (!flashResults.cancelled && !_.get(flashResults, [ 'results', 'bytesWritten' ])) {
           throw errors.createUserError({
             title: 'The writer process ended unexpectedly',
             description: 'Please try again, and contact the Etcher team if the problem persists',
@@ -206,7 +209,6 @@ exports.performWrite = (image, drive, onProgress) => {
         if (error.code === SIGKILL_EXIT_CODE) {
           error.code = 'ECHILDDIED'
         }
-
         return reject(error)
       }).finally(() => {
         console.log('Terminating IPC server')
@@ -219,7 +221,7 @@ exports.performWrite = (image, drive, onProgress) => {
 }
 
 /**
- * @summary Flash an image to a drive
+ * @summary Flash an image to drives
  * @function
  * @public
  *
@@ -227,17 +229,17 @@ exports.performWrite = (image, drive, onProgress) => {
  * This function will update `imageWriter.state` with the current writing state.
  *
  * @param {String} image - image path
- * @param {Object} drive - drive
+ * @param {Array<Object>} drives - drives
  * @returns {Promise}
  *
  * @example
- * imageWriter.flash('foo.img', {
+ * imageWriter.flash('foo.img', [{
  *   device: '/dev/disk2'
- * }).then(() => {
+ * }]).then(() => {
  *   console.log('Write completed!')
  * })
  */
-exports.flash = (image, drive) => {
+exports.flash = (image, drives) => {
   if (flashState.isFlashing()) {
     return Bluebird.reject(new Error('There is already a flash in progress'))
   }
@@ -246,7 +248,7 @@ exports.flash = (image, drive) => {
 
   const analyticsData = {
     image,
-    drive,
+    drives,
     uuid: flashState.getFlashUuid(),
     unmountOnSuccess: settings.get('unmountOnSuccess'),
     validateWriteOnSuccess: settings.get('validateWriteOnSuccess')
@@ -254,7 +256,7 @@ exports.flash = (image, drive) => {
 
   analytics.logEvent('Flash', analyticsData)
 
-  return exports.performWrite(image, drive, (state) => {
+  return exports.performWrite(image, drives, (state) => {
     flashState.setProgressState(state)
   }).then(flashState.unsetFlashingFlag).then(() => {
     if (flashState.wasLastFlashCancelled()) {

lib/gui/app/pages/main/controllers/flash.js

@@ -72,7 +72,7 @@ module.exports = function (
 
     const iconPath = '../../../assets/icon.png'
 
-    imageWriter.flash(image.path, drive).then(() => {
+    imageWriter.flash(image.path, [ drive ]).then(() => {
       if (!flashState.wasLastFlashCancelled()) {
         notification.send('Success!', {
           body: messages.info.flashComplete(path.basename(image.path), drive),

lib/gui/modules/child-writer.js

@@ -19,7 +19,7 @@
 const ipc = require('node-ipc')
 const EXIT_CODES = require('../../shared/exit-codes')
 const errors = require('../../shared/errors')
-const writer = require('../../cli/writer')
+const ImageWriter = require('../../sdk/writer')
 
 ipc.config.id = process.env.IPC_CLIENT_ID
 ipc.config.socketRoot = process.env.IPC_SOCKET_ROOT
@@ -64,7 +64,9 @@ const log = (message) => {
  */
 const terminate = (code) => {
   ipc.disconnect(IPC_SERVER_ID)
-  process.exit(code || EXIT_CODES.SUCCESS)
+  process.nextTick(() => {
+    process.exit(code || EXIT_CODES.SUCCESS)
+  })
 }
 
 /**
@@ -93,6 +95,7 @@ ipc.connectTo(IPC_SERVER_ID, () => {
   process.once('SIGINT', () => {
     terminate(EXIT_CODES.SUCCESS)
   })
+
   process.once('SIGTERM', () => {
     terminate(EXIT_CODES.SUCCESS)
   })
@@ -107,27 +110,65 @@ ipc.connectTo(IPC_SERVER_ID, () => {
     terminate(EXIT_CODES.SUCCESS)
   })
 
+  ipc.of[IPC_SERVER_ID].on('write', (options) => {
+    const destinations = [].concat(options.destinations)
+
+    log(`Image: ${options.imagePath}`)
+    log(`Devices: ${destinations.join(', ')}`)
+    log(`Umount on success: ${options.unmountOnSuccess}`)
+    log(`Validate on success: ${options.validateWriteOnSuccess}`)
+
+    let exitCode = EXIT_CODES.SUCCESS
+
+    /**
+     * @summary Progress handler
+     * @param {Object} state - progress state
+     * @example
+     * writer.on('progress', onProgress)
+     */
+    const onProgress = (state) => {
+      ipc.of[IPC_SERVER_ID].emit('state', state)
+    }
+
+    /**
+     * @summary Finish handler
+     * @param {Object} results - Flash results
+     * @example
+     * writer.on('finish', onFinish)
+     */
+    const onFinish = (results) => {
+      log(`Finish: ${results.bytesWritten}`)
+      ipc.of[IPC_SERVER_ID].emit('done', { results })
+      terminate(exitCode)
+    }
+
+    /**
+     * @summary Error handler
+     * @param {Error} error - error
+     * @example
+     * writer.on('error', onError)
+     */
+    const onError = (error) => {
+      log(`Error: ${error.message}`)
+      exitCode = EXIT_CODES.GENERAL_ERROR
+      ipc.of[IPC_SERVER_ID].emit('error', error)
+    }
+
+    const writer = new ImageWriter({
+      verify: options.validateWriteOnSuccess,
+      unmountOnSuccess: options.unmountOnSuccess,
+      checksumAlgorithms: options.checksumAlgorithms || []
+    })
+
+    writer.on('error', onError)
+    writer.on('progress', onProgress)
+    writer.on('finish', onFinish)
+
+    writer.write(options.imagePath, destinations)
+  })
+
   ipc.of[IPC_SERVER_ID].on('connect', () => {
     log(`Successfully connected to IPC server: ${IPC_SERVER_ID}, socket root ${ipc.config.socketRoot}`)
-    log(`Image: ${process.env.OPTION_IMAGE}`)
+    ipc.of[IPC_SERVER_ID].emit('ready', {})
-    log(`Device: ${process.env.OPTION_DEVICE}`)
-
-    // These come as strings containing 0 or 1. We need to convert
-    // them to numbers first, and then to booleans, otherwise something
-    // like `Boolean('0')` will be `true`
-    const unmountOnSuccess = Boolean(Number(process.env.OPTION_UNMOUNT))
-    const validateWriteOnSuccess = Boolean(Number(process.env.OPTION_VALIDATE))
-    log(`Umount on success: ${unmountOnSuccess}`)
-    log(`Validate on success: ${validateWriteOnSuccess}`)
-
-    writer.writeImage(process.env.OPTION_IMAGE, process.env.OPTION_DEVICE, {
-      unmountOnSuccess,
-      validateWriteOnSuccess
-    }, (state) => {
-      ipc.of[IPC_SERVER_ID].emit('state', state)
-    }).then((results) => {
-      ipc.of[IPC_SERVER_ID].emit('done', results)
-      terminate(EXIT_CODES.SUCCESS)
-    }).catch(handleError)
   })
 })

lib/sdk/image-stream/handlers.js

@@ -40,6 +40,13 @@ const errors = require('../../shared/errors')
  */
 const DEFAULT_EXT = 'img'
 
+/**
+ * @summary Default read-stream highWaterMark value (4M)
+ * @type {Number}
+ * @constant
+ */
+const STREAM_HWM = 4194304
+
 /**
  * @summary Image handlers
  * @namespace handlers
@@ -65,7 +72,7 @@ module.exports = {
       path: imagePath,
       archiveExtension: fileExtensions.getLastFileExtension(imagePath),
       extension: fileExtensions.getPenultimateFileExtension(imagePath) || DEFAULT_EXT,
-      stream: fs.createReadStream(imagePath),
+      stream: fs.createReadStream(imagePath, { highWaterMark: STREAM_HWM }),
       size: {
         original: options.size,
         final: {
@@ -105,7 +112,7 @@ module.exports = {
         path: imagePath,
         archiveExtension: fileExtensions.getLastFileExtension(imagePath),
         extension: fileExtensions.getPenultimateFileExtension(imagePath) || DEFAULT_EXT,
-        stream: fs.createReadStream(imagePath),
+        stream: fs.createReadStream(imagePath, { highWaterMark: STREAM_HWM }),
         size: {
           original: options.size,
           final: {
@@ -146,7 +153,7 @@ module.exports = {
         path: imagePath,
         archiveExtension: fileExtensions.getLastFileExtension(imagePath),
         extension: fileExtensions.getPenultimateFileExtension(imagePath) || DEFAULT_EXT,
-        stream: fs.createReadStream(imagePath),
+        stream: fs.createReadStream(imagePath, { highWaterMark: STREAM_HWM }),
         size: {
           original: options.size,
           final: {
@@ -177,7 +184,7 @@ module.exports = {
       return {
         path: imagePath,
         extension: fileExtensions.getLastFileExtension(imagePath),
-        stream: udif.createReadStream(imagePath),
+        stream: udif.createReadStream(imagePath, { highWaterMark: STREAM_HWM }),
         size: {
           original: options.size,
           final: {
@@ -231,7 +238,7 @@ module.exports = {
     return {
       path: imagePath,
       extension: fileExtensions.getLastFileExtension(imagePath),
-      stream: fs.createReadStream(imagePath),
+      stream: fs.createReadStream(imagePath, { highWaterMark: STREAM_HWM }),
       size: {
         original: options.size,
         final: {

lib/sdk/writer/block-write-stream.js

@@ -153,7 +153,7 @@ class BlockWriteStream extends stream.Writable {
         this.blocksWritten += 1
         this.position += bytesWritten
         this.retries = 0
-        next(error)
+        next()
         return
       }
 

lib/sdk/writer/index.js

@@ -37,6 +37,7 @@ const debug = require('debug')('etcher:writer')
 const _ = require('lodash')
 
 /* eslint-disable prefer-reflect */
+/* eslint-disable callback-return */
 
 /**
  * @summary Timeout, in milliseconds, to wait before unmounting on success
@@ -77,6 +78,36 @@ const runSeries = (tasks, callback) => {
   run()
 }
 
+/**
+ * @summary Helper function to run a set of async tasks in sequence
+ * @private
+ * @param {Array<Function>} tasks - set of tasks
+ * @param {Function} callback - callback(error)
+ * @example
+ * runParallel([
+ *   (next) => first(next),
+ *   (next) => second(next),
+ * ], (error) => {
+ *   // ...
+ * })
+ */
+const runParallel = (tasks, callback) => {
+  let count = tasks.length
+  const resultErrors = new Array(count).fill(null)
+  const results = new Array(count).fill(null)
+
+  tasks.forEach((task, index) => {
+    task((error, result) => {
+      count -= 1
+      resultErrors[index] = error
+      results[index] = result
+      if (count === 0) {
+        callback(resultErrors, results)
+      }
+    })
+  })
+}
+
 /**
  * @summary ImageWriter class
  * @class
@@ -85,8 +116,6 @@ class ImageWriter extends EventEmitter {
   /**
    * @summary ImageWriter constructor
    * @param {Object} options - options
-   * @param {String} options.imagePath - disk image path
-   * @param {String} options.path - dest path
    * @param {Boolean} options.verify - whether to verify the dest
    * @param {Boolean} options.unmountOnSuccess - whether to unmount the dest after flashing
    * @param {Array<String>} options.checksumAlgorithms - checksums to calculate
@@ -94,62 +123,83 @@ class ImageWriter extends EventEmitter {
    * new ImageWriter(options)
    */
   constructor (options) {
+    options = options || {}
     super()
 
-    this.options = options
+    debug('new', options)
+
+    this.unmountOnSuccess = Boolean(options.unmountOnSuccess)
+    this.verifyChecksums = Boolean(options.verify)
+    this.checksumAlgorithms = options.checksumAlgorithms || []
 
     this.source = null
     this.pipeline = null
-    this.target = null
+    this.destinations = new Map()
+
+    this.finished = false
+    this.hadError = false
 
     this.bytesRead = 0
     this.bytesWritten = 0
     this.checksum = {}
+
+    this.once('error', () => {
+      this.hadError = true
+    })
   }
 
   /**
-   * @summary Verify that the selected destination device exists
+   * @summary Verify that the selected destination devices exist
+   * @param {Array<String>} paths - target device paths
    * @param {Function} callback - callback(error)
    * @private
    * @example
-   * writer.checkSelectedDevice((error) => {
+   * writer.getSelectedDevices(['/dev/disk2'], (error, destinations) => {
    *   // ...
    * })
    */
-  checkSelectedDevice (callback) {
+  getSelectedDevices (paths, callback) {
-    debug('state:device-select', this.options.path)
+    debug('state:device-select', paths)
-    this.destinationDevice = null
     drivelist.list((error, drives) => {
-      debug('state:device-select', this.options.path, error ? 'NOT OK' : 'OK')
+      debug('state:device-select', paths, error ? 'NOT OK' : 'OK')
 
       if (error) {
         callback.call(this, error)
         return
       }
 
-      const selectedDrive = _.find(drives, {
+      const results = paths.map((path) => {
-        device: this.options.path
+        const destination = {
+          fd: null,
+          error: null,
+          stream: null,
+          finished: false,
+          verified: false,
+          device: _.find(drives, {
+            device: path
+          })
+        }
+
+        if (!destination.device) {
+          const selectionError = errors.createUserError({
+            title: `The selected drive "${path}" was not found`,
+            description: `We can't find "${path}" in your system. Did you unplug the drive?`,
+            code: 'EUNPLUGGED'
+          })
+          debug('state:device-select', destination, 'NOT OK')
+          destination.error = selectionError
+        }
+
+        return destination
       })
 
-      if (!selectedDrive) {
+      callback.call(this, null, results)
-        const selectionError = errors.createUserError({
-          title: 'The selected drive was not found',
-          description: `We can't find ${this.options.path} in your system. Did you unplug the drive?`,
-          code: 'EUNPLUGGED'
-        })
-        debug('state:device-select', this.options.path, 'NOT OK')
-        callback.call(this, selectionError)
-        return
-      }
-
-      this.destinationDevice = selectedDrive
-
-      callback.call(this)
     })
   }
 
   /**
    * @summary Unmount the destination device
+   * @param {Object} destination - destination object
    * @param {Function} callback - callback(error)
    * @private
    * @example
@@ -157,22 +207,23 @@ class ImageWriter extends EventEmitter {
    *   // ...
    * })
    */
-  unmountDevice (callback) {
+  unmountDevice (destination, callback) {
     if (os.platform() === 'win32') {
       callback.call(this)
       return
     }
 
-    debug('state:unmount', this.destinationDevice.device)
+    debug('state:unmount', destination.device.device)
 
-    mountutils.unmountDisk(this.destinationDevice.device, (error) => {
+    mountutils.unmountDisk(destination.device.device, (error) => {
-      debug('state:unmount', this.destinationDevice.device, error ? 'NOT OK' : 'OK')
+      debug('state:unmount', destination.device.device, error ? 'NOT OK' : 'OK')
       callback.call(this, error)
     })
   }
 
   /**
    * @summary Clean a device's partition table
+   * @param {Object} destination - destination object
    * @param {Function} callback - callback(error)
    * @private
    * @example
@@ -180,56 +231,42 @@ class ImageWriter extends EventEmitter {
    *   // ...
    * })
    */
-  removePartitionTable (callback) {
+  removePartitionTable (destination, callback) {
     if (os.platform() !== 'win32') {
       callback.call(this)
       return
     }
 
-    debug('state:clean', this.destinationDevice.device)
+    debug('state:clean', destination.device.device)
 
-    diskpart.clean(this.destinationDevice.device).asCallback((error) => {
+    diskpart.clean(destination.device.device).asCallback((error) => {
-      debug('state:clean', this.destinationDevice.device, error ? 'NOT OK' : 'OK')
+      debug('state:clean', destination.device.device, error ? 'NOT OK' : 'OK')
       callback.call(this, error)
     })
   }
 
   /**
    * @summary Open the source for reading
+   * @param {String} imagePath - path to source image
    * @param {Function} callback - callback(error)
    * @private
    * @example
-   * writer.openSource((error) => {
+   * writer.openSource('path/to/image.img', (error, source) => {
    *   // ...
    * })
    */
-  openSource (callback) {
+  openSource (imagePath, callback) {
-    debug('state:source-open', this.options.imagePath)
+    debug('state:source-open', imagePath)
-    imageStream.getFromFilePath(this.options.imagePath).asCallback((error, image) => {
+    imageStream.getFromFilePath(imagePath).asCallback((error, image) => {
-      debug('state:source-open', this.options.imagePath, error ? 'NOT OK' : 'OK')
+      debug('state:source-open', imagePath, error ? 'NOT OK' : 'OK')
-      if (error) {
+      this.source = image
-        callback.call(this, error)
+      callback.call(this, error, this.source)
-        return
-      }
-
-      if (!constraints.isDriveLargeEnough(this.destinationDevice, image)) {
-        const driveError = errors.createUserError({
-          title: 'The image you selected is too big for this drive',
-          description: 'Please connect a bigger drive and try again'
-        })
-        debug('state:source-open', this.options.imagePath, 'NOT OK')
-        callback.call(this, driveError)
-        return
-      }
-
-      this.options.image = image
-
-      callback.call(this)
     })
   }
 
   /**
    * @summary Open the destination for writing
+   * @param {Object} destination - destination object
    * @param {Function} callback - callback(error)
    * @private
    * @example
@@ -237,8 +274,8 @@ class ImageWriter extends EventEmitter {
    *   // ...
    * })
    */
-  openDestination (callback) {
+  openDestination (destination, callback) {
-    debug('state:destination-open', this.destinationDevice.raw)
+    debug('state:destination-open', destination.device.raw)
 
     /* eslint-disable no-bitwise */
     const flags = fs.constants.O_RDWR |
@@ -246,38 +283,93 @@ class ImageWriter extends EventEmitter {
       fs.constants.O_SYNC
     /* eslint-enable no-bitwise */
 
-    fs.open(this.destinationDevice.raw, flags, (error, fd) => {
+    fs.open(destination.device.raw, flags, (error, fd) => {
-      debug('state:destination-open', this.destinationDevice.raw, error ? 'NOT OK' : 'OK')
+      debug('state:destination-open', destination.device.raw, error ? 'NOT OK' : 'OK')
-      this.options.fd = fd
+      destination.fd = fd
       callback.call(this, error)
     })
   }
 
+  /**
+   * @summary Check a destinstation against the drive constraints
+   * @param {Object} destination - destination object
+   * @param {Function} callback - callback(error)
+   * @example
+   * this.checkDriveConstraints(destination, (error) => {
+   *   // ...
+   * })
+   */
+  checkDriveConstraints (destination, callback) {
+    let error = null
+
+    if (!constraints.isDriveLargeEnough(destination.device, this.source)) {
+      error = errors.createUserError({
+        title: 'The image you selected is too big for this drive',
+        description: 'Please connect a bigger drive and try again'
+      })
+    }
+
+    callback.call(this, error)
+  }
+
   /**
    * @summary Start the flashing process
+   * @param {String} imagePath - path to source image
+   * @param {Array<String>} destinationPaths - paths to target devices
    * @returns {ImageWriter} imageWriter
    * @example
-   * imageWriter.flash()
+   * imageWriter.write(source, destinations)
    *   .on('error', reject)
    *   .on('progress', onProgress)
    *   .on('finish', resolve)
    */
-  flash () {
+  write (imagePath, destinationPaths) {
-    const tasks = [
+    // Open the source image
-      (next) => { this.checkSelectedDevice(next) },
+    this.openSource(imagePath, (openError, source) => {
-      (next) => { this.unmountDevice(next) },
+      if (openError) {
-      (next) => { this.removePartitionTable(next) },
+        this.emit('error', openError)
-      (next) => { this.openSource(next) },
-      (next) => { this.openDestination(next) }
-    ]
-
-    runSeries(tasks, (error) => {
-      if (error) {
-        this.emit('error', error)
         return
       }
 
-      this.write()
+      // Open & prepare target devices
+      this.getSelectedDevices(destinationPaths, (error, destinations) => {
+        if (error) {
+          this.emit('error', error)
+          return
+        }
+
+        const notFound = _.find(destinations, (destination) => {
+          return Boolean(destination.error)
+        })
+
+        if (notFound) {
+          this.emit('error', notFound.error)
+          return
+        }
+
+        // Generate preparation tasks for all destinations
+        const tasks = destinations.map((destination) => {
+          this.destinations.set(destination.device.device, destination)
+          return (next) => {
+            runSeries([
+              (done) => { this.checkDriveConstraints(destination, done) },
+              (done) => { this.unmountDevice(destination, done) },
+              (done) => { this.removePartitionTable(destination, done) },
+              (done) => { this.openDestination(destination, done) }
+            ], (preparationError) => {
+              destination.error = preparationError
+              next(preparationError)
+            })
+          }
+        })
+
+        // Run the preparation tasks in parallel for each destination
+        runParallel(tasks, (resultErrors, results) => {
+          // We can start (theoretically) flashing now...
+          debug('write:prep:done', resultErrors)
+          this._write()
+        })
+      })
     })
 
     return this
@@ -289,23 +381,41 @@ class ImageWriter extends EventEmitter {
    * @example
    * imageWriter.write()
    */
-  write () {
+  _write () {
-    this._createWritePipeline(this.options)
+    this.pipeline = this._createWritePipeline()
-      .on('checksum', (checksum) => {
+
-        debug('write:checksum', checksum)
+    this.pipeline.on('checksum', (checksum) => {
-        this.checksum = checksum
+      debug('write:checksum', checksum)
-      })
+      this.checksum = checksum
-      .on('error', (error) => {
+    })
-        this.emit('error', error)
+
+    this.pipeline.on('error', (error) => {
+      this.emit('error', error)
+    })
+
+    this.pipeline.on('finish', (destination) => {
+      this.bytesRead = this.source.bytesRead
+
+      let finishedCount = 0
+
+      this.destinations.forEach((dest) => {
+        finishedCount += dest.finished ? 1 : 0
       })
 
-    this.target.on('finish', () => {
+      debug('write:finish', finishedCount, '/', this.destinations.size)
-      this.bytesRead = this.source.bytesRead
+
-      this.bytesWritten = this.target.bytesWritten
+      if (destination) {
-      if (this.options.verify) {
+        this.bytesWritten += destination.stream.bytesWritten
-        this.verify()
+      }
-      } else {
+
-        this._finish()
+      if (finishedCount === this.destinations.size) {
+        if (this.verifyChecksums) {
+          debug('write:verify')
+          this.verify()
+        } else {
+          debug('write:finish')
+          this._finish()
+        }
       }
     })
 
@@ -319,26 +429,82 @@ class ImageWriter extends EventEmitter {
    * imageWriter.verify()
    */
   verify () {
-    this._createVerifyPipeline(this.options)
+    const progressStream = new ProgressStream({
-      .on('error', (error) => {
+      length: this.bytesWritten,
+      time: 500
+    })
+
+    progressStream.resume()
+
+    progressStream.on('progress', (state) => {
+      state.type = 'check'
+      state.totalSpeed = 0
+      state.active = 0
+      this.destinations.forEach((destination) => {
+        if (!destination.verified && !destination.error) {
+          state.totalSpeed += destination.progress.state.speed
+          state.active += 1
+        }
+      })
+      state.speed = state.active
+        ? state.totalSpeed / state.active
+        : state.active
+      this.emit('progress', state)
+    })
+
+    this.destinations.forEach((destination) => {
+      // Don't verify errored destinations
+      if (destination.error || !destination.stream) {
+        return
+      }
+
+      const pipeline = this._createVerifyPipeline(destination)
+
+      pipeline.on('error', (error) => {
         this.emit('error', error)
       })
-      .on('checksum', (checksum) => {
+
+      pipeline.on('checksum', (checksum) => {
         debug('verify:checksum', this.checksum, '==', checksum)
+        destination.checksum = checksum
         if (!_.isEqual(this.checksum, checksum)) {
           const error = new Error(`Verification failed: ${JSON.stringify(this.checksum)} != ${JSON.stringify(checksum)}`)
           error.code = 'EVALIDATION'
+          destination.error = error
           this.emit('error', error)
         }
-        this._finish()
       })
-      .on('finish', () => {
-        debug('verify:end')
 
-        // NOTE: As the 'checksum' event only happens after
+      pipeline.on('finish', () => {
-        // the 'finish' event, we `._finish()` there instead of here
+        debug('verify:finish')
+
+        destination.verified = true
+        destination.progress = null
+        destination.stream = null
+
+        let finishedCount = 0
+
+        this.destinations.forEach((dest) => {
+          finishedCount += (dest.error || dest.verified) ? 1 : 0
+        })
+
+        if (finishedCount === this.destinations.size) {
+          debug('verify:complete')
+          progressStream.end()
+          this._finish()
+        }
       })
 
+      // NOTE: Normally we'd use `pipeline.pipe(progressStream)` here,
+      // but that leads to degraded performance
+      pipeline.on('readable', function () {
+        let chunk = null
+        while ((chunk = this.read())) {
+          progressStream.write(chunk)
+        }
+      })
+    })
+
     return this
   }
 
@@ -365,23 +531,43 @@ class ImageWriter extends EventEmitter {
    */
   _cleanup (callback) {
     debug('state:cleanup')
-    fs.close(this.options.fd, (closeError) => {
+    const tasks = []
-      debug('state:cleanup', closeError ? 'NOT OK' : 'OK')
-      if (!this.options.unmountOnSuccess) {
-        callback.call(this, closeError)
-        return
-      }
 
-      // Closing a file descriptor on a drive containing mountable
+    this.destinations.forEach((destination) => {
-      // partitions causes macOS to mount the drive. If we try to
+      tasks.push((next) => {
-      // unmount too quickly, then the drive might get re-mounted
+        runSeries([
-      // right afterwards.
+          (done) => {
-      setTimeout(() => {
+            if (destination.fd) {
-        mountutils.unmountDisk(this.destinationDevice.device, (error) => {
+              fs.close(destination.fd, done)
-          debug('state:cleanup', error ? 'NOT OK' : 'OK')
+              destination.fd = null
-          callback.call(this, error)
+            } else {
-        })
+              done()
-      }, UNMOUNT_ON_SUCCESS_TIMEOUT_MS)
+            }
+          },
+          (done) => {
+            if (!this.unmountOnSuccess) {
+              done()
+              return
+            }
+
+            // Closing a file descriptor on a drive containing mountable
+            // partitions causes macOS to mount the drive. If we try to
+            // unmount too quickly, then the drive might get re-mounted
+            // right afterwards.
+            setTimeout(() => {
+              mountutils.unmountDisk(destination.device.device, (error) => {
+                debug('state:cleanup', error ? 'NOT OK' : 'OK')
+                done(error)
+              })
+            }, UNMOUNT_ON_SUCCESS_TIMEOUT_MS)
+          }
+        ], next)
+      })
+    })
+
+    runParallel(tasks, (resultErrors, results) => {
+      debug('state:cleanup', resultErrors)
+      callback.call(this, resultErrors)
     })
   }
 
@@ -393,8 +579,8 @@ class ImageWriter extends EventEmitter {
    */
   _finish () {
     this._cleanup(() => {
+      this.finished = true
       this.emit('finish', {
-        drive: this.destinationDevice,
         bytesRead: this.bytesRead,
         bytesWritten: this.bytesWritten,
         checksum: this.checksum
@@ -405,28 +591,17 @@ class ImageWriter extends EventEmitter {
   /**
    * @summary Creates a write pipeline from given options
    * @private
-   * @param {Object} options - options
-   * @param {Object} options.image - source image
-   * @param {Number} [options.fd] - destination file descriptor
-   * @param {String} [options.path] - destination file path
-   * @param {String} [options.flags] - destination file open flags
-   * @param {String} [options.mode] - destination file mode
    * @returns {Pipage} pipeline
    * @example
-   * this._createWritePipeline({
+   * this._createWritePipeline()
-   *   image: sourceImage,
-   *   path: '/dev/rdisk2'
-   * })
    */
-  _createWritePipeline (options) {
+  _createWritePipeline () {
     const pipeline = new Pipage({
       readableObjectMode: true
     })
 
-    const image = options.image
-    const source = image.stream
     const progressOptions = {
-      length: image.size.original,
+      length: this.source.size.original,
       time: 500
     }
 
@@ -434,66 +609,94 @@ class ImageWriter extends EventEmitter {
 
     // If the final size is an estimation,
     // use the original source size for progress metering
-    if (image.size.final.estimation) {
+    if (this.source.size.final.estimation) {
       progressStream = new ProgressStream(progressOptions)
       pipeline.append(progressStream)
     }
 
-    const isPassThrough = image.transform instanceof stream.PassThrough
+    const isPassThrough = this.source.transform instanceof stream.PassThrough
 
     // If the image transform is a pass-through,
     // ignore it to save on the overhead
-    if (image.transform && !isPassThrough) {
+    if (this.source.transform && !isPassThrough) {
-      pipeline.append(image.transform)
+      pipeline.append(this.source.transform)
     }
 
     // If the final size is known precisely and we're not
     // using block maps, then use the final size for progress
-    if (!image.size.final.estimation && !image.bmap) {
+    if (!this.source.size.final.estimation && !this.source.bmap) {
-      progressOptions.length = image.size.final.value
+      progressOptions.length = this.source.size.final.value
       progressStream = new ProgressStream(progressOptions)
       pipeline.append(progressStream)
     }
 
-    if (image.bmap) {
+    if (this.source.bmap) {
-      const blockMap = BlockMap.parse(image.bmap)
+      const blockMap = BlockMap.parse(this.source.bmap)
       debug('write:bmap', blockMap)
       progressStream = new ProgressStream(progressOptions)
       pipeline.append(progressStream)
       pipeline.append(new BlockMap.FilterStream(blockMap))
     } else {
       debug('write:blockstream')
-      const checksumStream = new ChecksumStream({
-        objectMode: true,
-        algorithms: options.checksumAlgorithms
-      })
       pipeline.append(new BlockStream())
-      pipeline.append(checksumStream)
+      if (this.verifyChecksums) {
-      pipeline.bind(checksumStream, 'checksum')
+        const checksumStream = new ChecksumStream({
+          objectMode: true,
+          algorithms: this.checksumAlgorithms
+        })
+        pipeline.append(checksumStream)
+        pipeline.bind(checksumStream, 'checksum')
+      }
     }
 
-    const target = new BlockWriteStream({
+    this.destinations.forEach((destination) => {
-      fd: options.fd,
+      if (destination.error) {
-      autoClose: false
+        debug('pipeline:skip', destination.device.device)
+        return
+      }
+
+      destination.stream = new BlockWriteStream({
+        fd: destination.fd,
+        autoClose: false
+      })
+
+      destination.stream.once('finish', () => {
+        debug('finish:unpipe', destination.device.device)
+        destination.finished = true
+        pipeline.emit('finish', destination)
+        pipeline.unpipe(destination.stream)
+      })
+
+      destination.stream.once('error', (error) => {
+        debug('error:unpipe', destination.device.device)
+        destination.error = error
+        destination.finished = true
+        pipeline.unpipe(destination.stream)
+      })
+
+      pipeline.bind(destination.stream, 'error')
+      pipeline.pipe(destination.stream)
     })
 
     // Pipeline.bind(progressStream, 'progress');
     progressStream.on('progress', (state) => {
-      state.device = options.path
       state.type = 'write'
-      state.speed = target.speed
+      state.totalSpeed = 0
+      state.active = 0
+      this.destinations.forEach((destination) => {
+        if (!destination.finished && !destination.error) {
+          state.totalSpeed += destination.stream.speed
+          state.active += 1
+        }
+      })
+      state.speed = state.active
+        ? state.totalSpeed / state.active
+        : state.active
       this.emit('progress', state)
     })
 
-    pipeline.bind(source, 'error')
+    pipeline.bind(this.source.stream, 'error')
-    pipeline.bind(target, 'error')
+    this.source.stream.pipe(pipeline)
-
-    source.pipe(pipeline)
-      .pipe(target)
-
-    this.source = source
-    this.pipeline = pipeline
-    this.target = target
 
     return pipeline
   }
@@ -501,25 +704,18 @@ class ImageWriter extends EventEmitter {
   /**
    * @summary Creates a verification pipeline from given options
    * @private
-   * @param {Object} options - options
+   * @param {Object} destination - the destination object
-   * @param {Object} options.image - image
-   * @param {Number} [options.fd] - file descriptor
-   * @param {String} [options.path] - file path
-   * @param {String} [options.flags] - file open flags
-   * @param {String} [options.mode] - file mode
    * @returns {Pipage} pipeline
    * @example
-   * this._createVerifyPipeline({
+   * this._createVerifyPipeline()
-   *   path: '/dev/rdisk2'
-   * })
    */
-  _createVerifyPipeline (options) {
+  _createVerifyPipeline (destination) {
     const pipeline = new Pipage()
 
-    let size = this.bytesWritten
+    let size = destination.stream.bytesWritten
 
-    if (!options.image.size.final.estimation) {
+    if (!this.source.size.final.estimation) {
-      size = Math.max(this.bytesWritten, options.image.size.final.value)
+      size = Math.max(size, this.source.size.final.value)
     }
 
     const progressStream = new ProgressStream({
@@ -529,9 +725,9 @@ class ImageWriter extends EventEmitter {
 
     pipeline.append(progressStream)
 
-    if (options.image.bmap) {
+    if (this.source.bmap) {
       debug('verify:bmap')
-      const blockMap = BlockMap.parse(options.image.bmap)
+      const blockMap = BlockMap.parse(this.source.bmap)
       const blockMapStream = new BlockMap.FilterStream(blockMap)
       pipeline.append(blockMapStream)
 
@@ -543,14 +739,14 @@ class ImageWriter extends EventEmitter {
       })
     } else {
       const checksumStream = new ChecksumStream({
-        algorithms: options.checksumAlgorithms
+        algorithms: this.checksumAlgorithms
       })
       pipeline.append(checksumStream)
       pipeline.bind(checksumStream, 'checksum')
     }
 
     const source = new BlockReadStream({
-      fd: options.fd,
+      fd: destination.fd,
       autoClose: false,
       start: 0,
       end: size
@@ -558,17 +754,8 @@ class ImageWriter extends EventEmitter {
 
     pipeline.bind(source, 'error')
 
-    progressStream.on('progress', (state) => {
+    destination.stream = source.pipe(pipeline)
-      state.device = options.path
+    destination.progress = progressStream
-      state.type = 'check'
-      this.emit('progress', state)
-    })
-
-    this.target = null
-    this.source = source
-    this.pipeline = pipeline
-
-    source.pipe(pipeline).resume()
 
     return pipeline
   }

tests/gui/modules/image-writer.spec.js

@@ -29,7 +29,7 @@ describe('Browser: imageWriter', () => {
           sourceChecksum: '1234'
         })
 
-        imageWriter.flash('foo.img', '/dev/disk2').finally(() => {
+        imageWriter.flash('foo.img', [ '/dev/disk2' ]).finally(() => {
           m.chai.expect(flashState.isFlashing()).to.be.false
         })
       })
@@ -40,18 +40,18 @@ describe('Browser: imageWriter', () => {
           sourceChecksum: '1234'
         })
 
-        const writing = imageWriter.flash('foo.img', '/dev/disk2')
+        const writing = imageWriter.flash('foo.img', [ '/dev/disk2' ])
-        imageWriter.flash('foo.img', '/dev/disk2').catch(angular.noop)
+        imageWriter.flash('foo.img', [ '/dev/disk2' ]).catch(angular.noop)
         writing.finally(() => {
           m.chai.expect(this.performWriteStub).to.have.been.calledOnce
         })
       })
 
       it('should reject the second flash attempt', () => {
-        imageWriter.flash('foo.img', '/dev/disk2')
+        imageWriter.flash('foo.img', [ '/dev/disk2' ])
 
         let rejectError = null
-        imageWriter.flash('foo.img', '/dev/disk2').catch((error) => {
+        imageWriter.flash('foo.img', [ '/dev/disk2' ]).catch((error) => {
           rejectError = error
         }).finally(() => {
           m.chai.expect(rejectError).to.be.an.instanceof(Error)
@@ -73,13 +73,13 @@ describe('Browser: imageWriter', () => {
       })
 
       it('should set flashing to false when done', () => {
-        imageWriter.flash('foo.img', '/dev/disk2').catch(angular.noop).finally(() => {
+        imageWriter.flash('foo.img', [ '/dev/disk2' ]).catch(angular.noop).finally(() => {
           m.chai.expect(flashState.isFlashing()).to.be.false
         })
       })
 
       it('should set the error code in the flash results', () => {
-        imageWriter.flash('foo.img', '/dev/disk2').catch(angular.noop).finally(() => {
+        imageWriter.flash('foo.img', [ '/dev/disk2' ]).catch(angular.noop).finally(() => {
           const flashResults = flashState.getFlashResults()
           m.chai.expect(flashResults.errorCode).to.equal('FOO')
         })
@@ -92,7 +92,7 @@ describe('Browser: imageWriter', () => {
         })
 
         let rejection
-        imageWriter.flash('foo.img', '/dev/disk2').catch((error) => {
+        imageWriter.flash('foo.img', [ '/dev/disk2' ]).catch((error) => {
           rejection = error
         }).finally(() => {
           m.chai.expect(rejection).to.be.an.instanceof(Error)