initial idea

atom/browser/api/lib/auto-updater.coffee

@@ -1,4 +1,9 @@
-autoUpdater = process.atomBinding('auto_updater').autoUpdater
+switch process.platform
+  when 'darwin'
+    autoUpdater = process.atomBinding('auto_updater').autoUpdater
+  when 'win32'
+    autoUpdater = require('./auto-updater-win')
+
 EventEmitter = require('events').EventEmitter
 
 autoUpdater.__proto__ = EventEmitter.prototype

atom/browser/api/lib/auto-updater/auto-updater-win.coffee

@@ -0,0 +1,60 @@
+{EventEmitter} = require 'events'
+SquirrelUpdate = require './auto-updater/squirrel-update-win'
+
+class AutoUpdater
+  @__proto__ = EventEmitter.prototype
+
+  quitAndInstall: ->
+    # TODO
+
+  setFeedUrl: (@updateUrl) ->
+
+  checkForUpdates: ->
+    throw new Error('Update URL is not set') unless @updateUrl
+
+    @emit 'checking-for-update'
+
+    unless SquirrelUpdate.existsSync()
+      @emit 'update-not-available'
+      return
+
+    @downloadUpdate (error, update) =>
+      if error?
+        @emit 'update-not-available'
+        return
+
+      unless update?
+        @emit 'update-not-available'
+        return
+
+      @emit 'update-available'
+
+      @installUpdate (error) =>
+        if error?
+          @emit 'update-not-available'
+          return
+
+        @emit 'update-downloaded', {}, update.releaseNotes, update.version, new Date(), @updateUrl, => @quitAndInstall()
+
+  downloadUpdate: (callback) ->
+    SquirrelUpdate.spawn ['--download', @updateUrl], (error, stdout) ->
+      return callback(error) if error?
+
+      try
+        # Last line of output is the JSON details about the releases
+        json   = stdout.trim().split('\n').pop()
+        update = JSON.parse(json)?.releasesToApply?.pop?()
+      catch error
+        error.stdout = stdout
+        return callback(error)
+
+      callback(null, update)
+
+  installUpdate: (callback) ->
+    SquirrelUpdate.spawn(['--update', @updateUrl], callback)
+
+  supportsUpdates: ->
+    SquirrelUpdate.existsSync()
+
+
+module.exports = new AutoUpdater()

atom/browser/api/lib/auto-updater/squirrel-update-win.coffee

@@ -0,0 +1,42 @@
+ChildProcess = require 'child_process'
+fs           = require 'fs'
+path         = require 'path'
+
+appFolder             = path.resolve(process.execPath, '..') # i.e. my-app/app-0.1.13/
+rootApplicationFolder = path.resolve(appFolder, '..') # i.e. my-app/
+updateDotExe          = path.join(rootApplicationFolder, 'Update.exe')
+exeName               = path.basename(process.execPath)
+
+# Spawn a command and invoke the callback when it completes with an error
+# and the output from standard out.
+spawn = (command, args, callback) ->
+  stdout = ''
+
+  try
+    spawnedProcess = ChildProcess.spawn(command, args)
+  catch error
+    # Spawn can throw an error
+    process.nextTick -> callback?(error, stdout)
+    return
+
+  spawnedProcess.stdout.on 'data', (data) -> stdout += data
+
+  error = null
+  spawnedProcess.on 'error', (processError) -> error ?= processError
+  spawnedProcess.on 'close', (code, signal) ->
+    error ?= new Error("Command failed: #{signal ? code}") if code isnt 0
+    error?.code ?= code
+    error?.stdout ?= stdout
+    callback?(error, stdout)
+
+# Spawn the Update.exe with the given arguments and invoke the callback when
+# the command completes.
+spawnUpdate = (args, callback) ->
+  spawn(updateDotExe, args, callback)
+
+# Exports
+exports.spawn = spawnUpdate
+
+# Is the Update.exe installed with Atom?
+exports.existsSync = ->
+  fs.accessSync(updateDotExe, fs.R_OK)