Add Windows support to device init command

lib/actions/device.coffee

@@ -2,10 +2,9 @@ _ = require('lodash-contrib')
 async = require('async')
 resin = require('resin-sdk')
 os = require('os')
-fs = require('fs')
-progressStream = require('progress-stream')
 visuals = require('resin-cli-visuals')
 commandOptions = require('./command-options')
+drive = require('../drive/drive')
 
 exports.list =
 	signature: 'devices'
@@ -166,18 +165,6 @@ exports.init =
 	options: [ commandOptions.yes ]
 	permission: 'user'
 	action: (params, options, done) ->
-		if os.platform() is 'win32'
-			error = new Error('This functionality is only available on UNIX based systems for now.')
-			return done(error)
-
-		if not fs.existsSync(params.image)
-			error = new Error("Invalid OS image: #{params.image}")
-			return done(error)
-
-		if not fs.existsSync(params.device)
-			error = new Error("Invalid device: #{params.device}")
-			return done(error)
-
 		async.waterfall([
 
 			(callback) ->
@@ -190,27 +177,14 @@ exports.init =
 			(confirmed, callback) ->
 				return done() if not confirmed
 
-				imageFile = fs.createReadStream(params.image)
-				deviceFile = fs.createWriteStream(params.device)
-				imageFileSize = fs.statSync(params.image).size
+				progressBar = null
 
-				progress = progressStream
-					length: imageFileSize
-					time: 500
-
-				if not options.quiet
-					progressBar = new visuals.widgets.Progress('Writing device OS', imageFileSize)
-					progress.on 'progress', (status) ->
+				drive.writeImage params.device, params.image,
+					progress: not options.quiet
+					onProgress: (status) ->
+						progressBar ?= new visuals.widgets.Progress('Writing device OS', status.length)
 						progressBar.tick(status.delta)
-
-				imageFile
-					.pipe(progress)
-					.pipe(deviceFile)
-					.on 'error', (error) ->
-						if error.code is 'EBUSY'
-							error.message = "Try umounting #{error.path} first."
-						return callback(error)
-					.on('close', callback)
+				, callback
 
 		], done)
 

lib/drive/drive.coffee

@@ -0,0 +1,38 @@
+fs = require('fs')
+progressStream = require('progress-stream')
+
+exports.writeImage = (devicePath, imagePath, options = {}, callback = _.noop) ->
+
+	if not fs.existsSync(imagePath)
+		return callback(new Error("Invalid OS image: #{imagePath}"))
+
+	if not fs.existsSync(devicePath)
+		return callback(new Error("Invalid device: #{devicePath}"))
+
+	imageFile = fs.createReadStream(imagePath)
+
+	deviceFile = fs.createWriteStream devicePath,
+		# Required by Windows to work correctly
+		flags: 'r+'
+
+	imageFileSize = fs.statSync(imagePath).size
+
+	progress = progressStream
+		length: imageFileSize
+		time: 500
+
+	if options.progress
+		progress.on('progress', options.onProgress)
+
+	imageFile
+		.pipe(progress)
+		.pipe(deviceFile)
+
+		# TODO: We should make use of nodewindows.elevate()
+		# if we get an EPERM error.
+		.on 'error', (error) ->
+			if error.code is 'EBUSY'
+				error.message = "Try umounting #{error.path} first."
+			return callback(error)
+
+		.on('close', callback)