XO-Server can now drop priviledges.

config/local.yaml.dist

@@ -1,5 +1,35 @@
 # Note: Relative paths will be resolved from XO-Server's directory.
 
+#=====================================================================
+
+# It may be necessary to run XO-Server as a priviledged user (e.g.
+# `root`) for instance to allow the HTTP server to listen on a
+# [priviledged ports](http://www.w3.org/Daemon/User/Installation/PrivilegedPorts.html).
+#
+# To avoid security issues, XO-Server can drop its priviledges by
+# changing the user and the group is running with.
+#
+# Note: XO-Server will change them just after reading the
+# configuration.
+
+# User to run XO-Server as.
+#
+# Note: The user can be specified using either its name or its numeric
+# identifier.
+#
+# Default: undefined
+#user: 'nobody'
+
+# Group to run XO-Server as.
+#
+# Note: The group can be specified using either its name or its
+# numeric identifier.
+#
+# Default: undefined
+#group: 'nogroup'
+
+#=====================================================================
+
 # Configuration of the embedded HTTP server.
 http:
 
@@ -52,6 +82,8 @@ http:
   mounts:
     #'/': '/path/to/xo-web/dist/'
 
+#=====================================================================
+
 # Connection to the Redis server.
 redis:
     # Syntax: tcp://[db[:password]@]hostname[:port]

src/fibers-utils.coffee

@@ -21,7 +21,8 @@ $sleep = (ms) ->
   setTimeout (-> fiber.run()), ms
   $fiber.yield()
 
-# Makes an asynchrouneous function synchrouneous (in a fiber).
+# Makes an Node like asynchrouneous function synchrouneous (in a
+# fiber).
 $synchronize = (fn, ctx) ->
   fn = ctx[fn] if $_.isString fn
 
@@ -33,22 +34,46 @@ $synchronize = (fn, ctx) ->
         fiber.throwInto error
       else
         fiber.run result
-    result = fn.apply ctx, args
+    fn.apply ctx, args
-
-    # A promise can only be detected once the function has been
-    # called.
-    if $isPromise result
-      result.then(
-        (result) -> fiber.run result
-        (error) -> fiber.throwInto error
-      )
 
     $fiber.yield()
 
+# Waits for an event.
+#
+# Note: if the *error* event is emitted, this function will throw.
+$waitEvent = (emitter, event) ->
+  fiber = $fiber.current
+
+  errorHandler = null
+  handler = (args...) ->
+    emitter.removeListener 'error', errorHandler
+    fiber.run args
+  errorHandler = (error) ->
+    emitter.removeListener event, handler
+    fiber.throwInto error
+
+  emitter.once event, handler
+  emitter.once 'error', errorHandler
+
+  $fiber.yield()
+
+# Waits for a promise to be fulfilled or broken.
+$waitPromise = (promise) ->
+  fiber = $fiber.current
+
+  promise.then(
+    (result) -> fiber.run result
+    (error) -> fiber.throwInto error
+  )
+
+  $fiber.yield()
+
 #=====================================================================
 
 module.exports = {
   $fiberize
   $sleep
   $synchronize
+  $waitEvent
+  $waitPromise
 }

src/main.coffee

@@ -25,7 +25,7 @@ $Session = require './session'
 $XO = require './xo'
 
 # Helpers for dealing with fibers.
-{$fiberize, $synchronize} = require './fibers-utils'
+{$fiberize, $synchronize, $waitEvent} = require './fibers-utils'
 
 # HTTP/HTTPS server which can listen on multiple ports.
 $WebServer = require './web-server'
@@ -112,6 +112,20 @@ do $fiberize ->
     if $nconf.get entry
       console.warn "[Warn] `#{entry}` configuration is deprecated."
 
+  # Creates the web server according to the configuration.
+  webServer = new $WebServer()
+  webServer.listen options for options in $nconf.get 'http:listen'
+
+  # Waits for the web server to start listening to drop priviledges.
+  $waitEvent webServer, 'listening'
+  try
+    if (group = $nconf.get 'group')?
+      process.setgid group
+    if (user = $nconf.get 'user')?
+      process.setuid user
+  catch error
+    console.warn "[WARN] Failed to change the user or group: #{error.message}"
+
   # Creates the main object which will connects to Xen servers and
   # manages all the models.
   xo = new $XO()
@@ -123,10 +137,6 @@ do $fiberize ->
     }
   }
 
-  # Creates the web server according to the configuration.
-  webServer = new $WebServer()
-  webServer.listen options for options in $nconf.get 'http:listen'
-
   # Static file serving (e.g. for XO-Web).
   connect = $connect()
   for urlPath, filePaths of $nconf.get 'http:mounts'

src/web-server.coffee

@@ -42,6 +42,7 @@ class $WebServer extends $EventEmitter
 
   constructor: ->
     @_servers = []
+    @_notYetListening = 0
 
   close: ->
     server.close() for server in @_servers
@@ -65,8 +66,10 @@ class $WebServer extends $EventEmitter
     else
       server.listen port, host
 
+    ++@_notYetListening
+
     # Helpful message.
-    server.once 'listening', ->
+    server.once 'listening', =>
       address = server.address()
       if $_.isObject address
         {address, port} = address
@@ -74,6 +77,10 @@ class $WebServer extends $EventEmitter
 
       console.log "WebServer listening on #{address}"
 
+      # If the web server is listening on all addresses, fire the
+      # `listening` event.
+      @emit 'listening' unless --@_notYetListening
+
     # Forwards events to this object.
     $_.each $events, (event) =>
       server.on event, (args...) => @emit event, args...

src/xo.coffee

@@ -28,7 +28,7 @@ $Model = require './model'
 $XAPI = require './xapi'
 
 # Helpers for dealing with fibers.
-{$fiberize, $synchronize} = require './fibers-utils'
+{$fiberize, $synchronize, $waitPromise} = require './fibers-utils'
 
 #=====================================================================
 
@@ -266,8 +266,7 @@ class $XO
           throw error unless error[0] is 'SESSION_NOT_REGISTERED'
 
     # Connects to existing servers.
-    getServers = $synchronize 'get', @servers
+    connect server for server in $waitPromise @servers.get()
-    connect server for server in getServers()
 
     # Automatically connects to new servers.
     @servers.on 'add', (servers) ->