WEB API机制分析

2. BatteryManager

2.1. 介绍

BatteryManager提供了访问系统电源管理级别信息的方式。

navigator.getBattery返回一个battery promise，你能够用这个经过这个promise来与Battery Status API进行交互。

navigator.getBattery().then(function(battery){     console.log("Battery charging? "+(battery.charging ?"Yes":"No"));   console.log("Battery level: "+ battery.level *100+"%");   console.log("Battery charging time: "+ battery.chargingTime +" seconds");   console.log("Battery discharging time: "+ battery.dischargingTime +" seconds");     battery.addEventListener('chargingchange', function(){     console.log("Battery charging? "+(battery.charging ?"Yes":"No"));   });     battery.addEventListener('levelchange', function(){     console.log("Battery level: "+ battery.level *100+"%");   });     battery.addEventListener('chargingtimechange', function(){     console.log("Battery charging time: "+ battery.chargingTime +" seconds");   });     battery.addEventListener('dischargingtimechange', function(){     console.log("Battery discharging time: "+ battery.dischargingTime +" seconds");   });   });

2.2. 原理分析

2.2.1. BatteryManager的初始化

当js代码执行到"app://system.gaiamobile.org/js/battery_manager.js":14中的_battery: window.navigator.battery时候，会建立C++的BatteryManager对象(其对应的实如今BatteryManager.cpp (gecko\dom\battery)文件中)：

(gdb) call DumpJSStack() 0<TOP LEVEL>["app://system.gaiamobile.org/js/battery_manager.js":14]     this=[object Window]

对应的C++代码代码执行堆栈以下：

#0  mozilla::hal_impl::GetCurrentBatteryInformation (     aBatteryInfo=0xb64162b8<mozilla::hal::sBatteryObservers+8>)     at ../../gecko/hal/gonk/GonkHal.cpp:438 #1  0xb4f59f1c in GetCurrentInformation (     this=0xb64162b0<mozilla::hal::sBatteryObservers>)     at ../../gecko/hal/Hal.cpp:248 #2  mozilla::hal::GetCurrentBatteryInformation (aInfo=aInfo@entry=0xbecef7e0)     at ../../gecko/hal/Hal.cpp:360 #3  0xb53bbdb8 in mozilla::dom::battery::BatteryManager::Init (this=0xa9aebc80)     at ../../../gecko/dom/battery/BatteryManager.cpp:42 #4  0xb53a08ce in mozilla::dom::Navigator::GetBattery (this=0xa96d2620,     aRv=...) at ../../../gecko/dom/base/Navigator.cpp:1410 #5  0xb5208970 in mozilla::dom::NavigatorBinding::get_battery (cx=0xaa4c0f80,     obj=..., self=<optimized out>, args=...) at NavigatorBinding.cpp:1596 #6  0xb52bdefa in mozilla::dom::GenericBindingGetter (cx=0xaa4c0f80,     argc=<optimized out>, vp=<optimized out>)     at ../../../gecko/dom/bindings/BindingUtils.cpp:2217 #7  0xb5c8dcd2 in CallJSNative (args=...,     native=0xb52bde65<mozilla::dom::GenericBindingGetter(JSContext*,unsignedint, JS::Value*)>, cx=0xaa4c0f80) at ../../../gecko/js/src/jscntxtinlines.h:239 #8  js::Invoke (cx=cx@entry=0xaa4c0f80, args=...,

会从hal::BatteryInformation中获取level，charging，remainingTime信息，存储在gecko层。其实现原理是从/sys/class/power_supply/battery/目录的文件中读取信息，capacity文件存储当前充电的进度(0~100)，status存储充电状态(Charging或者Full)，charging_source存储充电的源(0:BATTERY_NOT_CHARGING,1:BATTERY_CHARGING_USB,2:BATTERY_CHARGING_AC)。

2.2.2. Js属性访问

在js层BatteryManager 有4个只读属性：charging，chargingTime，dischargingTime，level，其对应的C实现见BatteryManagerBinding.cpp (objdir-gecko\dom\bindings)

对应的实现函数为get_charging，get_chargingTime，get_dischargingTime，get_level；而后分别调用mozilla::dom::battery::BatteryManager中的对应函数，直接读取mLevel，mCharging，mRemainingTime的值；当为充电状态的时候mRemainingTime的值做为chargingTime值，不然做为dischargingTime的值。

2.2.3. 状态回调

回调注册流程跟其余的public mozilla::dom::EventTarget中的on事件注册流程相同，经过

IMPL_EVENT_HANDLER(chargingchange)   IMPL_EVENT_HANDLER(chargingtimechange)   IMPL_EVENT_HANDLER(dischargingtimechange)   IMPL_EVENT_HANDLER(levelchange)

staticbool set_onchargingchange(JSContext* cx, JS::Handle<JSObject*> obj, mozilla::dom::battery::BatteryManager* self, JSJitSetterCallArgs args) {   nsRefPtr<EventHandlerNonNull> arg0;   if(args[0].isObject()){       {// Scope for tempRoot         JS::Rooted<JSObject*> tempRoot(cx,&args[0].toObject());         arg0 =new EventHandlerNonNull(tempRoot, mozilla::dom::GetIncumbentGlobal());       }     }else{     arg0 =nullptr;   }   self->SetOnchargingchange(Constify(arg0));     returntrue; }

最终直接向BatteryManager的事件处理管理器中注册回调函数，此处细节能够参考《gecko消息机制分析.docx》文档的3.5.1节。

当状态改变时，调用流程以下：

#0  mozilla::dom::battery::BatteryManager::Notify (this=0xa994dc00,     aBatteryInfo=...) at ../../../gecko/dom/battery/BatteryManager.cpp:104 #1  0xb4f59f7a in Broadcast (aParam=..., this=0xb6a35398)     at ../dist/include/mozilla/Observer.h:67 #2  BroadcastInformation (aInfo=...,     this=0xb64162b0<mozilla::hal::sBatteryObservers>)     at ../../gecko/hal/Hal.cpp:227 #3  BroadcastCachedInformation (     this=0xb64162b0<mozilla::hal::sBatteryObservers>)     at ../../gecko/hal/Hal.cpp:259 #4  mozilla::hal::NotifyBatteryChange (aInfo=...)     at ../../gecko/hal/Hal.cpp:368 #5  0xb4f5bf76 in mozilla::hal_impl::(anonymous namespace)::BatteryUpdater::Run     (this=<optimized out>) at ../../gecko/hal/gonk/GonkHal.cpp:290

109     DispatchTrustedEvent(LEVELCHANGE_EVENT_NAME); (gdb) p previousLevel $3 =0.95999999999999996 (gdb) p mLevel $4 =0.96999999999999997

通过DispatchTrustedEvent后会最终回调到注册的JS代码中。

3. Geolocation

3.1. 介绍

地理位置 API 容许用户向 Web 应用程序提供他们的位置。出于隐私考虑，报告地理位置前会先请求用户许可。地理位置 API 经过navigator.geolocation提供。若是该对象存在，那么地理位置服务可用。

if("geolocation" in navigator){   /* 地理位置服务可用 */ }else{   /* 地理位置服务不可用 */ }

3.1.1. 获取当前定位

您能够调用getCurrentPosition()函数获取用户当前定位位置。这会异步地请求获取用户位置，并查询定位硬件来获取最新信息。当定位被肯定后，定义的回调函数就会被执行。您能够选择性地提供第二个回调函数，当有错误时会被执行。第三个参数也是可选的，您能够经过该对象参数设定最长可接受的定位返回时间、等待请求的时间和是否获取高精度定位。

注意:默认状况下，getCurrentPosition()会尽快返回一个低精度结果，这在您不关心准确度只关心快速获取结果的状况下颇有用。有 GPS 的设备可能须要一分钟或更久来获取 GPS 定位，在这种状况下getCurrentPosition()会返回低精度数据（基于 IP 的定位或 Wi-Fi 定位）。

navigator.geolocation.getCurrentPosition(function(position){   do_something(position.coords.latitude, position.coords.longitude); });

上述示例中，当获取位置后 do_something() 函数会被执行。

3.1.2. 监视定位

您能够设定一个回调函数来响应定位数据发生的变动（设备发生了移动，或获取到了更高精度的地理位置信息）。您能够经过watchPosition()函数实现该功能。它与getCurrentPosition()接受相同的参数，但回调函数会被调用屡次。错误回调函数与getCurrentPosition()中同样是可选的，也会被屡次调用。

注意:您能够直接调用watchPosition()函数，不须要先调用getCurrentPosition()函数。

var watchID = navigator.geolocation.watchPosition(function(position){   do_something(position.coords.latitude, position.coords.longitude); });

watchPosition()函数会返回一个 ID，惟一地标记该位置监视器。您能够将这个 ID 传给clearWatch()函数来中止监视用户位置。

navigator.geolocation.clearWatch(watchID);

3.1.3. 调整返回结果

getCurrentPosition()和watchPosition()都接受一个成功回调、一个可选的失败回调和一个可选的 PositionOptions 对象。

对watchPosition的调用相似于这样:

function geo_success(position){   do_something(position.coords.latitude, position.coords.longitude); }   function geo_error(){   alert("Sorry, no position available."); }   var geo_options ={   enableHighAccuracy:true,   maximumAge        :30000,   timeout           :27000 };   var wpid = navigator.geolocation.watchPosition(geo_success, geo_error, geo_options);

watchPosition 实际使用示例: http://www.thedotproduct.org/experiments/geo/

3.1.4. 描述位置

用户的位置由一个包含 Coordinates 对象的 Position 对象描述。

3.1.5. 处理错误

getCurrentPosition() 或 watchPosition() 的错误回调函数以 PositionError 为第一个参数。

function errorCallback(error){   alert('ERROR('+ error.code +'): '+ error.message); };

3.2. 地理位置示例

function geoFindMe(){   var output = document.getElementById("out");     if(!navigator.geolocation){     output.innerHTML ="<p><您的浏览器不支持地理位置</p>";     return;   }     function success(position){     var latitude  = position.coords.latitude;     var longitude = position.coords.longitude;       output.innerHTML ='<p><Latitude is '+ latitude + '° Longitude is ' + longitude + '°</p>';       var img =new Image();     img.src ="http://maps.googleapis.com/maps/api/staticmap?center="+ latitude +","+ longitude +"&zoom=13&size=300x300&sensor=false";       output.appendChild(img);   };     function error(){     output.innerHTML ="没法获取您的位置";   };     output.innerHTML ="<p><Locating…</p>";     navigator.geolocation.getCurrentPosition(success, error); }

3.2.1. 受权请求

全部 addons.mozilla.org 上须要使用地理位置的插件必须在使用 API 前显式地请求权限。用户的响应将会存储在 pref 参数指定的偏好设置中。callback 参数指定的函数会被调用并包含一个表明用户响应的 boolean 参数。若是为 true，表明插件能够访问地理位置数据。

function prompt(window, pref, message, callback){     let branch = Components.classes["@mozilla.org/preferences-service;1"]                            .getService(Components.interfaces.nsIPrefBranch);       if(branch.getPrefType(pref)=== branch.PREF_STRING){         switch(branch.getCharPref(pref)){         case"always":             return callback(true);         case"never":             return callback(false);         }     }       let done =false;       function remember(value, result){         return function(){             done =true;             branch.setCharPref(pref, value);             callback(result);         }     }       let self = window.PopupNotifications.show(         window.gBrowser.selectedBrowser,         "geolocation",         message,         "geo-notification-icon",         {             label:"Share Location",             accessKey:"S",             callback: function(notification){                 done =true;                 callback(true);             }         },[             {                 label:"Always Share",                 accessKey:"A",                 callback: remember("always",true)             },             {                 label:"Never Share",                 accessKey:"N",                 callback: remember("never",false)             }         ],{             eventCallback: function(event){                 if(event ==="dismissed"){                     if(!done) callback(false);                     done =true;                     window.PopupNotifications.remove(self);                 }             },             persistWhileVisible:true         }); }   prompt(window,        "extensions.foo-addon.allowGeolocation",        "Foo Add-on wants to know your location.",        function callback(allowed){ alert(allowed);});

3.3. 原理分析

3.3.1. 初始化

 

Geolocation* Navigator::GetGeolocation(ErrorResult& aRv) {   if(mGeolocation){     return mGeolocation;   }     if(!mWindow ||!mWindow->GetOuterWindow()||!mWindow->GetDocShell()){     aRv.Throw(NS_ERROR_FAILURE);     returnnullptr;   }     mGeolocation =new Geolocation();   if(NS_FAILED(mGeolocation->Init(mWindow->GetOuterWindow()))){     mGeolocation =nullptr;     aRv.Throw(NS_ERROR_FAILURE);     returnnullptr;   }     return mGeolocation; }

 

 

4. MozAlarmsManager

4.1. 介绍

navigator.mozAlarms是一个MozAlarmsManager对象。MozAlarmsManager容许在指定的时间点弹出一个notifications通知或者启动一个app。

接口定义以下：

interface MozAlarmsManager {   DOMRequest getAll();   DOMRequest add(Date date, DOMString respectTimezone, optional object data);   void remove(unsignedlong id); };

MozAlarmsManager.getAll():获取当前全部设定的alarms列表。

MozAlarmsManager.add():设定一个新的alarm

MozAlarmsManager.remove():删除一个已经存在的alarm

4.1.1. getAll

获取当前全部设定的alarms列表。

var request = navigator.mozAlarms.getAll();   request.onsuccess = function (){   console.log('operation successful:'+this.result.length +'alarms pending');     this.result.forEach(function (alarm){     console.log(alarm.id +' : '+ alarm.date.toString()+' : '+ alarm.respectTimezone);      }); }   request.onerror = function (){   console.log('operation failed: '+this.error); }

navigator.mozAlarms.getAll();返回一个DOMRequest对象，能够处理success和error消息。this.result是一个匿名的数组对象，每个对象含有下面的属性：

id：表明alarm的id的一个数字。

Date：一个Date类型的对象，表明了设定的alarm的时间。

respectTimezone：一个字串，表示是否关心时区，值为“ignoreTimezone”或者“honorTimezone”

data：一个JS对象，存储了alarm的相关信息。

4.2. 原理分析

查看Navigator.cpp (gecko\dom\base)及NavigatorBinding.cpp (objdir-gecko\dom\bindings)都没有发现alarm相关的实现。查看omni\components\components.manifest中有以下定义

component {fea1e884-9b05-11e1-9b64-87a7016c3860} AlarmsManager.js contract @mozilla.org/alarmsManager;1{fea1e884-9b05-11e1-9b64-87a7016c3860} category JavaScript-navigator-property mozAlarms @mozilla.org/alarmsManager;1

可知，MozAlarms的实如今AlarmsManager.js中。

4.2.1. 初始化

全部的JS代码实现的navigator的对象都是在第一个对象被访问时会把全部的信息都加载进来，可是此时只加载被访问的JS对象的代码，方便后面的访问。

Line 24: category JavaScript-navigator-property mozPermissionSettings @mozilla.org/permissionSettings;1     Line 29: category JavaScript-navigator-property mozAlarms @mozilla.org/alarmsManager;1     Line 73: category JavaScript-navigator-property mozWifiManager @mozilla.org/wifimanager;1     Line 90: category JavaScript-navigator-property mozNetworkStats @mozilla.org/networkStatsManager;1     Line 203: category JavaScript-navigator-property mozApps @mozilla.org/webapps;1     Line 228: category JavaScript-navigator-property mozId @mozilla.org/dom/identity;1     Line 248: category JavaScript-navigator-property mozTCPSocket @mozilla.org/tcp-socket;1     Line 255: category JavaScript-navigator-property mozPay @mozilla.org/payment/content-helper;1     Line 262: category JavaScript-navigator-property mozKeyboard @mozilla.org/b2g-keyboard;1

即上面9个对象中的任何一个被访问到就会所有加载对应信息，在我们7715手机上debug的结果是最早访问到wifimanager对象，其调用堆栈以下：

Breakpoint 1, nsScriptNameSpaceManager::OperateCategoryEntryHash (     this=this@entry=0xb24a7be0, aCategoryManager=aCategoryManager@entry=     0xb6a64ec0,     aCategory=aCategory@entry=0xb5ef8b80"JavaScript-navigator-property",     aEntry=0xb1311d60, aRemove=aRemove@entry=false)     at ../../../gecko/dom/base/nsScriptNameSpaceManager.cpp:625 625     type = nsGlobalNameStruct::eTypeNavigatorProperty; (gdb) bt #0  nsScriptNameSpaceManager::OperateCategoryEntryHash (     this=this@entry=0xb24a7be0,     aCategoryManager=aCategoryManager@entry=0xb6a64ec0,     aCategory=aCategory@entry=0xb5ef8b80"JavaScript-navigator-property",     aEntry=0xb1311d60, aRemove=aRemove@entry=false)     at ../../../gecko/dom/base/nsScriptNameSpaceManager.cpp:625 #1  0xb53b4ad6 in nsScriptNameSpaceManager::AddCategoryEntryToHash (     this=this@entry=0xb24a7be0,     aCategoryManager=aCategoryManager@entry=0xb6a64ec0,     aCategory=aCategory@entry=0xb5ef8b80"JavaScript-navigator-property",     aEntry=<optimized out>)     at ../../../gecko/dom/base/nsScriptNameSpaceManager.cpp:749 #2  0xb53b4b18 in nsScriptNameSpaceManager::FillHash (     this=this@entry=0xb24a7be0, aCategoryManager=0xb6a64ec0,     aCategory=0xb5ef8b80"JavaScript-navigator-property")     at ../../../gecko/dom/base/nsScriptNameSpaceManager.cpp:198 #3  0xb53b4c2a in nsScriptNameSpaceManager::Init (this=0xb24a7be0)     at ../../../gecko/dom/base/nsScriptNameSpaceManager.cpp:374 #4  0xb53960d6 in mozilla::dom::GetNameSpaceManager ()     at ../../../gecko/dom/base/nsJSEnvironment.cpp:3120 #5  0xb53a614e in nsDOMClassInfo::Init ()     at ../../../gecko/dom/base/nsDOMClassInfo.cpp:895 #6  0xb53a819c in NS_GetDOMClassInfoInstance ( ---Type <return> to continue,or q <return> to quit---     aID=eDOMClassInfo_ChromeMessageBroadcaster_id)     at ../../../gecko/dom/base/nsDOMClassInfo.cpp:1742 #7  0xb54f0a84 in QueryInterface (aInstancePtr=0xbea5326c, aIID=...,     this=0xb24a7b20)     at ../../../../gecko/content/base/src/nsFrameMessageManager.cpp:126 #8  nsFrameMessageManager::QueryInterface (this=0xb24a7b20, aIID=...,     aInstancePtr=0xbea5326c)     at ../../../../gecko/content/base/src/nsFrameMessageManager.cpp:90 #9  0xb4d514f4 in nsQueryInterface::operator() (this=this@entry=0xbea53264,     aIID=..., answer=answer@entry=0xbea5326c)     at ../../../gecko/xpcom/glue/nsCOMPtr.cpp:14

(gdb) call DumpJSStack() 0 WifiWorker()["jar:file:///system/b2g/omni.ja!/components/WifiWorker.js":1642]     this=[object Object] 1 anonymous(outer = null, iid ={c04f3102-1ce8-4d57-9c27-8aece9c2740a})["resource://gre/modules/XPCOMUtils.jsm":271]     this=[object Object]

其中会表示加载全部JS对象的关键代码在下面的这个循环中：(nsScriptNameSpaceManager.cpp (gecko\dom\base)) ，其中aCategory的值就是"JavaScript-navigator-property"，会循环获取里面的值AddCategoryEntryToHash。

nsresult nsScriptNameSpaceManager::FillHash(nsICategoryManager *aCategoryManager,                                    constchar*aCategory) {   nsCOMPtr<nsISimpleEnumerator> e;   nsresult rv = aCategoryManager->EnumerateCategory(aCategory,                                                     getter_AddRefs(e));   NS_ENSURE_SUCCESS(rv, rv);     nsCOMPtr<nsISupports> entry;   while(NS_SUCCEEDED(e->GetNext(getter_AddRefs(entry)))){     rv = AddCategoryEntryToHash(aCategoryManager, aCategory, entry);     if(NS_FAILED(rv)){       return rv;     }   }     return NS_OK; }

当JS对象被访问时才会执行对象的构造函数，而且会默认执行init函数，其调用堆栈以下：

#0  mozilla::dom::ConstructJSImplementation (aCx=aCx@entry=0xaf671ed0,     aContractId=<optimized out>, aGlobal=..., aObject=..., aObject@entry=...,     aRv=...) at ../../../gecko/dom/bindings/BindingUtils.cpp:2028 #1  0xb526a05a in ConstructNavigatorObjectHelper (aRv=..., global=...,     cx=0xaf671ed0) at SettingsManagerBinding.cpp:1015 #2  mozilla::dom::SettingsManagerBinding::ConstructNavigatorObject (     aCx=0xaf671ed0, aObj=...) at SettingsManagerBinding.cpp:1032 #3  0xb53a0af0 in mozilla::dom::Navigator::DoNewResolve (     this=this@entry=0xab950c10, aCx=aCx@entry=0xaf671ed0,     aObject=aObject@entry=..., aId=..., aId@entry=..., aDesc=...)     at ../../../gecko/dom/base/Navigator.cpp:1886 #4  0xb52042ae in mozilla::dom::NavigatorBinding::_newResolve (cx=0xaf671ed0,     obj=..., id=..., flags=<optimized out>, objp=...)     at NavigatorBinding.cpp:2311 #5  0xb5c2604a in CallResolveOp (propp=..., objp=..., id=..., obj=...,     cx=<optimized out>, recursedp=<synthetic pointer>, flags=<optimized out>)     at ../../../gecko/js/src/jsobj.cpp:3921 #6  LookupOwnPropertyWithFlagsInline<(js::AllowGC)1> (     donep=<synthetic pointer>, propp=..., objp=..., id=..., obj=...,     flags=<optimized out>, cx=<optimized out>)     at ../../../gecko/js/src/jsobj.cpp:4011 #7  LookupPropertyWithFlagsInline<(js::AllowGC)1> (propp=..., objp=...,     flags=65535, id=..., obj=..., cx=0xaf671ed0) ---Type <return> to continue,or q <return> to quit---     at ../../../gecko/js/src/jsobj.cpp:4072 #8  js::baseops::LookupProperty<(js::AllowGC)1> (cx=0xaf671ed0, obj=...,     id=..., objp=..., propp=...) at ../../../gecko/js/src/jsobj.cpp:4113

再次回到咱们当前关注的MozAlarms，当第一次被访问时，会加载对应的实现文件AlarmsManager.js，而且会执行对应的init函数。

AlarmsManager.js (gecko\dom\alarm)

const{ classes: Cc, interfaces: Ci, utils: Cu, results: Cr }= Components;   Cu.import("resource://gre/modules/XPCOMUtils.jsm"); Cu.import("resource://gre/modules/Services.jsm"); Cu.import("resource://gre/modules/DOMRequestHelper.jsm");   const ALARMSMANAGER_CONTRACTID ="@mozilla.org/alarmsManager;1"; const ALARMSMANAGER_CID        = Components.ID("{fea1e884-9b05-11e1-9b64-87a7016c3860}"); const nsIDOMMozAlarmsManager   = Ci.nsIDOMMozAlarmsManager; const nsIClassInfo             = Ci.nsIClassInfo;   function AlarmsManager() {   debug("Constructor"); }

// nsIDOMGlobalPropertyInitializer implementation   init: function init(aWindow){     debug("init()");       // Set navigator.mozAlarms to null.     if(!Services.prefs.getBoolPref("dom.mozAlarms.enabled")){       return null;     }       // Only pages with perm set can use the alarms.     let principal = aWindow.document.nodePrincipal;     let perm =       Services.perms.testExactPermissionFromPrincipal(principal,"alarms");     if(perm != Ci.nsIPermissionManager.ALLOW_ACTION){       return null;     }       // SystemPrincipal documents do not have any origin.     // Reject them for now.     if(!principal.URI){       return null;     }       this._cpmm = Cc["@mozilla.org/childprocessmessagemanager;1"]                    .getService(Ci.nsISyncMessageSender);       // Add the valid messages to be listened.     this.initDOMRequestHelper(aWindow,["AlarmsManager:Add:Return:OK",                                         "AlarmsManager:Add:Return:KO",                                         "AlarmsManager:GetAll:Return:OK",                                         "AlarmsManager:GetAll:Return:KO"]);       // Get the manifest URL if this is an installed app     let appsService = Cc["@mozilla.org/AppsService;1"]                         .getService(Ci.nsIAppsService);     this._pageURL = principal.URI.spec;     this._manifestURL = appsService.getManifestURLByLocalId(principal.appId);     this._window = aWindow;   },     // Called from DOMRequestIpcHelper.   uninit: function uninit(){     debug("uninit()");   }, }

因而可知会加载Services.jsm，DOMRequestHelper.jsm，而且定义当前的component对应的CID和IID值，加载CPMM和appsService，推测后续是须要进行IPC消息发送的。

4.2.2. getAll

navigator.mozAlarms.getAll()的调用是在客户端进程中的，实现流程以下(AlarmsManager.js)：

getAll: function getAll(){     debug("getAll()");       let request =this.createRequest();     this._cpmm.sendAsyncMessage(       "AlarmsManager:GetAll",       { requestId:this.getRequestId(request), manifestURL:this._manifestURL }     );     return request;   },

DOMRequestHelper.jsm (gecko\dom\base)      9431     2014/12/1：   createRequest: function(){     return Services.DOMRequest.createRequest(this._window);   },

DOMRequest.cpp (gecko\dom\base) NS_IMETHODIMP DOMRequestService::CreateRequest(nsIDOMWindow* aWindow,                                  nsIDOMDOMRequest** aRequest) {   nsCOMPtr<nsPIDOMWindow> win(do_QueryInterface(aWindow));   NS_ENSURE_STATE(win);   NS_ADDREF(*aRequest =new DOMRequest(win));     return NS_OK; }

能够看出this.createRequest()返回的是DOMRequest对象。

下面接着分析this.getRequestId(request)的做用：

DOMRequestHelper.jsm (gecko\dom\base)   getRequestId: function(aRequest){     if(!this._requests){       this._requests ={};     }       let id ="id"+this._getRandomId();     this._requests[id]= aRequest;     return id;   },

能够看出其做用是将new出来的DOMRequest保存在this对象里面，并转换为一个ID值，这样作的目的是为了在IPC通讯回来后能够找到对应的DOMRequest，而且将result值设置好，从而在success和error消息中能够访问到返回的数据。

最后this._cpmm.sendAsyncMessage的目的是发送IPC消息，具体流程请参考《gecko消息机制分析.docx》，发送过去的"AlarmsManager:GetAll"，并经过_manifestURL标识客户端的进程信息。

在B2G进程中，处理"AlarmsManager:GetAll"消息的代码实如今AlarmService.jsm (gecko\dom\alarm)文件中的receiveMessage中，以下：

receiveMessage: function receiveMessage(aMessage){     debug("receiveMessage(): "+ aMessage.name);     let json = aMessage.json;       // To prevent the hacked child process from sending commands to parent     // to schedule alarms, we need to check its permission and manifest URL.     if(this._messages.indexOf(aMessage.name)!=-1){       if(!aMessage.target.assertPermission("alarms")){         debug("Got message from a child process with no 'alarms' permission.");         return null;       }       if(!aMessage.target.assertContainApp(json.manifestURL)){         debug("Got message from a child process containing illegal manifest URL.");         return null;       }     }       let mm = aMessage.target.QueryInterface(Ci.nsIMessageSender);     switch(aMessage.name){       case"AlarmsManager:GetAll":         this._db.getAll(           json.manifestURL,           function getAllSuccessCb(aAlarms){             debug("Callback after getting alarms from database: "+                   JSON.stringify(aAlarms));             this._sendAsyncMessage(mm,"GetAll",true, json.requestId, aAlarms);           }.bind(this),           function getAllErrorCb(aErrorMsg){             this._sendAsyncMessage(mm,"GetAll",false, json.requestId, aErrorMsg);           }.bind(this)         );         break;           default:         throw Components.results.NS_ERROR_NOT_IMPLEMENTED;         break;     }   },

首选获得客户端传说过来的JSON数据，即{ requestId: this.getRequestId(request), manifestURL: this._manifestURL }，经过manifestURL检查是否有获取alarm的权限(这个权限是在app的manifest中申请的，在B2G加载应用信息的时候保持在进程中的)。

而后经过数据库操做_db.getAll()获取alarms的信息，最后经过_sendAsyncMessage将信息经过IPC消息传给客户端。

下面分析_db.getAll()和_sendAsyncMessage的细节，先看_db.getAll()，全部alarm的数据库都在AlarmDB.jsm (gecko\dom\alarm)中实现的。

/**    * @param aManifestURL    *        The manifest URL of the app that alarms belong to.    *        If null, directly return all alarms; otherwise,    *        only return the alarms that belong to this app.    * @param aSuccessCb    *        Callback function to invoke with result array.    * @param aErrorCb [optional]    *        Callback function to invoke when there was an error.    */   getAll: function getAll(aManifestURL, aSuccessCb, aErrorCb){     debug("getAll()");       this.newTxn(       "readonly",       ALARMSTORE_NAME,       function txnCb(aTxn, aStore){         if(!aTxn.result){           aTxn.result =[];         }           let index = aStore.index("manifestURL");         index.mozGetAll(aManifestURL).onsuccess = function setTxnResult(aEvent){           aTxn.result = aEvent.target.result;           debug("Request successful. Record count: "+ aTxn.result.length);         };       },       aSuccessCb,       aErrorCb     );   }

具体数据库处理细节这里就不分析了，咱们看存储在数据库中的项，即返回的object所含有的属性值：

upgradeSchema: function upgradeSchema(aTransaction, aDb, aOldVersion, aNewVersion){     debug("upgradeSchema()");       let objectStore = aDb.createObjectStore(ALARMSTORE_NAME,{ keyPath:"id", autoIncrement:true});       objectStore.createIndex("date",           "date",           { unique:false});     objectStore.createIndex("ignoreTimezone","ignoreTimezone",{ unique:false});     objectStore.createIndex("timezoneOffset","timezoneOffset",{ unique:false});     objectStore.createIndex("data",           "data",           { unique:false});     objectStore.createIndex("pageURL",        "pageURL",        { unique:false});     objectStore.createIndex("manifestURL",    "manifestURL",    { unique:false});       debug("Created object stores and indexes");   },

其中红色的4个值是与alarm信息相关的，也是须要传回去的。

下面继续分析_sendAsyncMessage：

_sendAsyncMessage: function _sendAsyncMessage(aMessageManager, aMessageName,                                                 aSuccess, aRequestId, aData){     debug("_sendAsyncMessage()");       if(!aMessageManager){       debug("Invalid message manager: null");       throw Components.results.NS_ERROR_FAILURE;     }       let json = null;     switch(aMessageName)     {       case"GetAll":         json = aSuccess ?           {requestId: aRequestId, alarms: aData}:           { requestId: aRequestId, errorMsg: aData };         break;         default:         throw Components.results.NS_ERROR_NOT_IMPLEMENTED;         break;     }       aMessageManager.sendAsyncMessage("AlarmsManager:" + aMessageName +                                      ":Return:" +(aSuccess ? "OK" : "KO"), json);   },

能够看出若是成功则返回消息AlarmsManager:GetAll:Return:OK，并将返回的数据做为alarms，出错则返回AlarmsManager:GetAll:Return:KO.

在客户端AlarmsManager.js (gecko\dom\alarm)中的receiveMessage处理返回的消息：

receiveMessage: function receiveMessage(aMessage){     debug("receiveMessage(): "+ aMessage.name);       let json = aMessage.json;     let request =this.getRequest(json.requestId);       if(!request){       debug("No request stored! "+ json.requestId);       return;     }       switch(aMessage.name){       case"AlarmsManager:GetAll:Return:OK":         // We don't need to expose everything to the web content.         let alarms =[];         json.alarms.forEach(function trimAlarmInfo(aAlarm){           let alarm ={ "id":              aAlarm.id,                         "date":            aAlarm.date,                         "respectTimezone": aAlarm.ignoreTimezone ?                                              "ignoreTimezone" : "honorTimezone",                         "data":            aAlarm.data };           alarms.push(alarm);         });         Services.DOMRequest.fireSuccess(request,                                         Cu.cloneInto(alarms,this._window));         break;         case"AlarmsManager:GetAll:Return:KO":         Services.DOMRequest.fireError(request, json.errorMsg);         break;         default:         debug("Wrong message: "+ aMessage.name);         break;     }     this.removeRequest(json.requestId);    },

先经过返回的ID来getRequest(json.requestId)，而后将返回的数组中的数据转换为alarms数组，最后经过fireSuccess或者fireError回调到onsucess或者onerror。

综上所述：全部的alarms信息到保存在一个数据库中，只有B2G进程才有权限读取数据库；客户端须要查询本身应用的alarms的时候，经过发送IPC消息到B2G进行查询，B2G进程先检查权限，而后从数据库中查询发请求的app的全部alarms返回回来。

对应的时序图以下：

另外两个接口add和remove的处理逻辑相似，不一样只是发送的消息和代入的参数不一样，转换为数据库操做的时候分别对应add和remove操做。

5. mozApps

5.1. 介绍

navigator.mozApps是一个Apps对象，能够经过apps来安装管理和控制一个open web app。

Apps对象含有的属性：DOMApplicationsRegistry.mgmt；方法有：DOMApplicationsRegistry.checkInstalled()，DOMApplicationsRegistry.install()，DOMApplicationsRegistry.getSelf()，DOMApplicationsRegistry.getInstalled()。

5.1.1. DOMApplicationsRegistry.mgmt

DOMApplicationsManager类型的对象，能够容许用户在界面上(dashboards??)进行app的管理和启动。

var mgmt = navigator.mozApps.mgmt;

5.1.1.1. DOMApplicationsManager.oninstall

当接收到install事件的时候被触发。

5.1.1.2. DOMApplicationsManager.onuninstall

当接收到uninstall事件的时候被触发。

5.1.1.3. OMApplicationsManager.onenablestatechange

当接收到enablestatechange事件的时候被触发。

5.1.1.4. DOMApplicationsManager.getAll

返回全部的apps。

5.1.2. DOMApplicationsRegistry.checkInstalled

获取指定的app的信息，经过这个接口能够判断app是否被安装了，传入的url为app的manifest。

var request = window.navigator.mozApps.checkInstalled(url);

返回一个DOMRequest对象，DOMRequest.result属性是一个DOMApplication对象，描述了被安装的app的信息，若是应用没有被安装，则为null。

{   manifest:{     name:"Add-on Builder",     default_locale:"en",     installs_allowed_from:[       "https://apps-preview-dev.example.com/",       "https://apps-preview.example.com/"     ],     description:"Add-on Builder makes it easy to write, build and test Firefox extensions using common web technologies.",     version:"0.9.16.1",     developer:{       url:"https://builder.addons.mozilla.org/",       name:"Mozilla Flightdeck Team"     }   },   origin:"https://builder-addons-dev.example.com",   installTime:1321986882773,   installOrigin:"https://apps-preview-dev.example.com",   receipts:["h0dHBzOi8v (most of receipt removed here) Tg2ODtkUp"] }

var request = window.navigator.mozApps.checkInstalled("http://example.com/manifest.webapp"); request.onerror = function(e){   alert("Error calling checkInstalled: "+ request.error.name); }; request.onsuccess = function(e){   if(request.result){     console.log("App is installed!");   }   else{     console.log("App is not installed!");   } };

若是请求获取的app的domain与当前的app不是domain则在函数调用后当即返回以讹NS_ERROR_DOM_BAD_URI的错误。

5.1.3. DOMApplicationsRegistry.install

触发安装一个app，在安装的过程当中，应用须要进行验证而且弹出提示框让用户进行确认。若是这个app以前从相同的domain中安装过，调用install()会覆盖原来已经存在的安装数据。

var request = window.navigator.mozApps.install(manifestUrl); request.onsuccess = function (){   // Save the App object that is returned   var appRecord =this.result;   alert('Installation successful!'); }; request.onerror = function (){   // Display the error information from the DOMError object   alert('Install failed, error: '+this.error.name); };

5.1.4. DOMApplicationsRegistry.getSelf

获取当前应用的app信息。返回一个DOMRequest对象，若是成功DOMRequest.result属性是一个DOMApplication对象，描述了被安装的app的信息，失败则为null。

var request = window.navigator.mozApps.getSelf(); request.onsuccess = function(){   if(request.result){     // Pull the name of the app out of the App object     alert("Name of current app: "+ request.result.manifest.name);   }else{     alert("Called from outside of an app");   } }; request.onerror = function(){   // Display error name from the DOMError object   alert("Error: "+ request.error.name); };

5.1.5. DOMApplicationsRegistry.getInstalled

获取从当前的orgin安装的app列表，例如若是在Marketplace中调用这个接口则返回全部从Marketplace中安装的app列表。

var request = window.navigator.mozApps.getInstalled(); request.onerror = function(e){   alert("Error calling getInstalled: "+ request.error.name); }; request.onsuccess = function(e){   alert("Success, number of apps: "+ request.result.length);   var appsRecord = request.result; };

若是success则，request.result为app对象的数组。

5.2. 原理分析

查看Navigator.cpp (gecko\dom\base)及NavigatorBinding.cpp (objdir-gecko\dom\bindings)都没有发现mozApps相关的实现。查看omni\components\ components.manifest中有以下定义。

component {fff440b3-fae2-45c1-bf03-3b5a2e432270} Webapps.js contract @mozilla.org/webapps;1{fff440b3-fae2-45c1-bf03-3b5a2e432270} category JavaScript-navigator-property mozApps @mozilla.org/webapps;1

可知，mozApps的实如今Webapps.js中。咱们查看Webapps.js，发现里面有多个对象定义，查找CID为fff440b3-fae2-45c1-bf03-3b5a2e432270的对象为WebappsRegistry，能够肯定mozApps对应在gecko的实现为WebappsRegistry对象。

function WebappsRegistry(){ }   WebappsRegistry.prototype={   __proto__: DOMRequestIpcHelper.prototype,     classID: Components.ID("{fff440b3-fae2-45c1-bf03-3b5a2e432270}"),     QueryInterface: XPCOMUtils.generateQI([Ci.nsISupportsWeakReference,                                          Ci.nsIObserver,                                          Ci.mozIDOMApplicationRegistry,                                          Ci.mozIDOMApplicationRegistry2,                                          Ci.nsIDOMGlobalPropertyInitializer]),     classInfo: XPCOMUtils.generateCI({classID: Components.ID("{fff440b3-fae2-45c1-bf03-3b5a2e432270}"),                                     contractID:"@mozilla.org/webapps;1",                                     interfaces:[Ci.mozIDOMApplicationRegistry,                                                  Ci.mozIDOMApplicationRegistry2],                                     flags: Ci.nsIClassInfo.DOM_OBJECT,                                     classDescription:"Webapps Registry"}) }

5.2.1. 初始化

// nsIDOMGlobalPropertyInitializer implementation   init: function(aWindow){     this.initDOMRequestHelper(aWindow,"Webapps:Install:Return:OK");       let util =this._window.QueryInterface(Ci.nsIInterfaceRequestor)                            .getInterface(Ci.nsIDOMWindowUtils);     this._id = util.outerWindowID;     cpmm.sendAsyncMessage("Webapps:RegisterForMessages",                           { messages:["Webapps:Install:Return:OK"]});       let principal = aWindow.document.nodePrincipal;     let perm = Services.perms                .testExactPermissionFromPrincipal(principal,"webapps-manage");       // Only pages with the webapps-manage permission set can get access to     // the mgmt object.     this.hasMgmtPrivilege = perm == Ci.nsIPermissionManager.ALLOW_ACTION;   },     classID: Components.ID("{fff440b3-fae2-45c1-bf03-3b5a2e432270}"),     QueryInterface: XPCOMUtils.generateQI([Ci.nsISupportsWeakReference,                                          Ci.nsIObserver,                                          Ci.mozIDOMApplicationRegistry,                                          Ci.mozIDOMApplicationRegistry2,                                          Ci.nsIDOMGlobalPropertyInitializer]),     classInfo: XPCOMUtils.generateCI({classID: Components.ID("{fff440b3-fae2-45c1-bf03-3b5a2e432270}"),                                     contractID:"@mozilla.org/webapps;1",                                     interfaces:[Ci.mozIDOMApplicationRegistry,                                                  Ci.mozIDOMApplicationRegistry2],                                     flags: Ci.nsIClassInfo.DOM_OBJECT,                                     classDescription:"Webapps Registry"}) }

能够看出app向B2G注册了"Webapps:Install:Return:OK，对应的消息是在Webapps.jsm (gecko\dom\apps\src)中处理的，当B2G进程发出消息，会通知到B2G的Webapps.jsm，而后经过IPC消息转发到app的Webapps.js，WebappsRegistry的receiveMessage会进行处理。

5.2.2. DOMApplicationsRegistry.mgmt

Mgmt()函数返回一个WebappsApplicationMgmt对象。

get mgmt(){     if(!this.hasMgmtPrivilege){       return null;     }       if(!this._mgmt)       this._mgmt =new WebappsApplicationMgmt(this._window);     returnthis._mgmt;   },

WebappsApplicationMgmt的构造函数中作了以下事情：

function WebappsApplicationMgmt(aWindow){   this.initDOMRequestHelper(aWindow,["Webapps:GetAll:Return:OK",                                       "Webapps:GetAll:Return:KO",                                       "Webapps:Uninstall:Return:OK",                                       "Webapps:Uninstall:Broadcast:Return:OK",                                       "Webapps:Uninstall:Return:KO",                                       "Webapps:Install:Return:OK",                                       "Webapps:GetNotInstalled:Return:OK"]);     cpmm.sendAsyncMessage("Webapps:RegisterForMessages",                         {                           messages:["Webapps:Install:Return:OK",                                      "Webapps:Uninstall:Return:OK",                                      "Webapps:Uninstall:Broadcast:Return:OK"]                         }                        );     this._oninstall = null;   this._onuninstall = null; }

能够看出app向B2G注册了"Webapps:Install:Return:OK"和"Webapps:Uninstall:Return:OK"及"Webapps:Uninstall:Broadcast:Return:OK"，对应的消息是在Webapps.jsm (gecko\dom\apps\src)中处理的，当B2G进程发出这些消息，会通知到B2G的Webapps.jsm，而后经过IPC消息转发到app的Webapps.js，WebappsRegistry的receiveMessage会进行处理，同时receiveMessage还会处理initDOMRequestHelper中注册的其余消息。

5.2.3. DOMApplicationsRegistry.checkInstalled

checkInstalled: function(aManifestURL){     let manifestURL = Services.io.newURI(aManifestURL, null,this._window.document.baseURIObject);     this._window.document.nodePrincipal.checkMayLoad(manifestURL,true,false);       let request =this.createRequest();       this.addMessageListeners("Webapps:CheckInstalled:Return:OK");     cpmm.sendAsyncMessage("Webapps:CheckInstalled",{ origin:this._getOrigin(this._window.location.href),                                                       manifestURL: manifestURL.spec,                                                       oid:this._id,                                                       requestID:this.getRequestId(request)});     return request;   },

主要工做是经过CPMM发送了Webapps:CheckInstalled消息。这个消息是在Webapps.jsm (gecko\dom\apps\src)的receiveMessage中处理的

case"Webapps:CheckInstalled":         this.checkInstalled(msg, mm);         break;

checkInstalled: function(aData, aMm){     aData.app = null;     let tmp =[];       for(let appId in this.webapps){       if(this.webapps[appId].manifestURL == aData.manifestURL &&           this._isLaunchable(this.webapps[appId])){         aData.app= AppsUtils.cloneAppObject(this.webapps[appId]);         tmp.push({ id: appId });         break;       }     }       this._readManifests(tmp).then((aResult)=>{       for(let i =0; i < aResult.length; i++){         aData.app.manifest= aResult[i].manifest;         break;       }       aMm.sendAsyncMessage("Webapps:CheckInstalled:Return:OK", aData);     });   },

从this.webapps[](即DOMApplicationRegistry. Webapps[])数组中查找与传入的manifestURL相同的app，而后分别读取app的manifest信息，将app信息和manifest信息都做为返回参数aData的属性传回，并返回消息"Webapps:CheckInstalled:Return:OK"。

其中this.webapps[]的信息是在loadCurrentRegistry中初始化的。

// loads the current registry, that could be empty on first run.   loadCurrentRegistry: function(){     returnAppsUtils.loadJSONAsync(this.appsFile).then((aData)=>{       if(!aData){         return;       }         this.webapps = aData;       let appDir = OS.Path.dirname(this.appsFile);       for(let id in this.webapps){         let app =this.webapps[id];         if(!app){           deletethis.webapps[id];           continue;         }           app.id = id;           // Make sure we have a localId         if(app.localId === undefined){           app.localId =this._nextLocalId();         }           if(app.basePath === undefined){           app.basePath = appDir;         }           // Default to removable apps.         if(app.removable === undefined){           app.removable =true;         }           // Default to a non privileged status.         if(app.appStatus === undefined){           app.appStatus = Ci.nsIPrincipal.APP_STATUS_INSTALLED;         }           // Default to NO_APP_ID and not in browser.         if(app.installerAppId === undefined){           app.installerAppId = Ci.nsIScriptSecurityManager.NO_APP_ID;         }         if(app.installerIsBrowser === undefined){           app.installerIsBrowser =false;         }           // Default installState to "installed", and reset if we shutdown         // during an update.         if(app.installState === undefined ||             app.installState ==="updating"){           app.installState ="installed";         }           // Default storeId to "" and storeVersion to 0         if(this.webapps[id].storeId === undefined){           this.webapps[id].storeId ="";         }         if(this.webapps[id].storeVersion === undefined){           this.webapps[id].storeVersion =0;         }           // Default role to "".         if(this.webapps[id].role === undefined){           this.webapps[id].role ="";         }           // At startup we can't be downloading, and the $TMP directory         // will be empty so we can't just apply a staged update.         app.downloading =false;         app.readyToApplyDownload =false;       }     });   },

在我们7715手机上对应的文件是root@scx15_sp7715ga:/system/b2g/webapps # cat webapps.json，里面的信息以下截图，读取后成为一个object数组。

B2G返回的"Webapps:CheckInstalled:Return:OK"消息是在Webapps.js (gecko\dom\apps\src)的receiveMessage中处理的：

receiveMessage: function(aMessage){     let msg = aMessage.json;     if(msg.oid !=this._id)       return     let req =this.getRequest(msg.requestID);     if(!req)       return;     let app = msg.app;     switch(aMessage.name){       case"Webapps:CheckInstalled:Return:OK":         this.removeMessageListeners(aMessage.name);         Services.DOMRequest.fireSuccess(req, msg.app);         break;       }     this.removeRequest(msg.requestID);   },

直接将B2G返回的app信息回调给onsuccess.

5.2.4. DOMApplicationsRegistry.install

DOMApplicationsRegistry.install的实现体在Webapps.js (gecko\dom\apps\src)中实现以下：

install: function(aURL, aParams){     let request =this.createRequest();       let uri =this._validateURL(aURL, request);       if(uri &&this._ensureForeground(request)){       this.addMessageListeners("Webapps:Install:Return:KO");       cpmm.sendAsyncMessage("Webapps:Install",                             this._prepareInstall(uri, request, aParams,false));     }       return request;   },

 

能够看出主要是经过CPMM向B2G发送了"Webapps:Install"消息，其中传递给B2G的数据是经过_prepareInstall来构造的，主要：

_prepareInstall: function(aURL, aRequest, aParams, isPackage){     let installURL =this._window.location.href;     let requestID =this.getRequestId(aRequest);     let receipts =(aParams && aParams.receipts &&                     Array.isArray(aParams.receipts))? aParams.receipts                                                      :[];     let categories =(aParams && aParams.categories &&                       Array.isArray(aParams.categories))? aParams.categories                                                          :[];       let principal =this._window.document.nodePrincipal;       return{app:{                     installOrigin:this._getOrigin(installURL),                     origin:this._getOrigin(aURL),                     manifestURL: aURL,                     receipts: receipts,                     categories: categories                   },                from: installURL,              oid:this._id,              requestID: requestID,              appId: principal.appId,              isBrowser: principal.isInBrowserElement,              isPackage: isPackage            };   },

在B2G进程中处理"Webapps:Install"消息在Webapps.jsm文件的receiveMessage中：

case"Webapps:Install":{         this.doInstall(msg, mm);         break;       }

// Downloads the manifest and run checks, then eventually triggers the   // installation UI.   doInstall: function doInstall(aData, aMm){     let app = aData.app;       let sendError = function sendError(aError){       aData.error = aError;       aMm.sendAsyncMessage("Webapps:Install:Return:KO", aData);       Cu.reportError("Error installing app from: "+ app.installOrigin +                      ": "+ aError);     }.bind(this);       if(app.receipts.length >0){       for(let receipt of app.receipts){         let error =this.isReceipt(receipt);         if(error){           sendError(error);           return;         }       }     }       // Hosted apps can't be trusted or certified, so just check that the     // manifest doesn't ask for those.     function checkAppStatus(aManifest){       let manifestStatus = aManifest.type ||"web";       return manifestStatus ==="web";     }       let checkManifest =(function(){       if(!app.manifest){         sendError("MANIFEST_PARSE_ERROR");         returnfalse;       }         // Disallow multiple hosted apps installations from the same origin for now.       // We will remove this code after multiple apps per origin are supported (bug 778277).       // This will also disallow reinstalls from the same origin for now.       for(let id in this.webapps){         if(this.webapps[id].origin == app.origin &&             !this.webapps[id].packageHash &&             this._isLaunchable(this.webapps[id])){           sendError("MULTIPLE_APPS_PER_ORIGIN_FORBIDDEN");           returnfalse;         }       }         if(!AppsUtils.checkManifest(app.manifest, app)){         sendError("INVALID_MANIFEST");         returnfalse;       }         if(!AppsUtils.checkInstallAllowed(app.manifest, app.installOrigin)){         sendError("INSTALL_FROM_DENIED");         returnfalse;       }         if(!checkAppStatus(app.manifest)){         sendError("INVALID_SECURITY_LEVEL");         returnfalse;       }         returntrue;     }).bind(this);       let installApp =(function(){       app.manifestHash =this.computeManifestHash(app.manifest);       // We allow bypassing the install confirmation process to facilitate       // automation.       let prefName ="dom.mozApps.auto_confirm_install";       if(Services.prefs.prefHasUserValue(prefName)&&           Services.prefs.getBoolPref(prefName)){         this.confirmInstall(aData);       }else{         Services.obs.notifyObservers(aMm,"webapps-ask-install",                                      JSON.stringify(aData));       }     }).bind(this);       // We may already have the manifest (e.g. AutoInstall),     // in which case we don't need to load it.     if(app.manifest){       if(checkManifest()){         installApp();       }       return;     }       let xhr = Cc["@mozilla.org/xmlextras/xmlhttprequest;1"]                 .createInstance(Ci.nsIXMLHttpRequest);     xhr.open("GET", app.manifestURL,true);     xhr.channel.loadFlags |= Ci.nsIRequest.INHIBIT_CACHING;     xhr.channel.notificationCallbacks =this.createLoadContext(aData.appId,                                                                aData.isBrowser);     xhr.responseType ="json";       xhr.addEventListener("load",(function(){       if(xhr.status ==200){         if(!AppsUtils.checkManifestContentType(app.installOrigin, app.origin,                                                 xhr.getResponseHeader("content-type"))){           sendError("INVALID_MANIFEST");           return;         }           app.manifest = xhr.response;         if(checkManifest()){           app.etag = xhr.getResponseHeader("Etag");           installApp();         }       }else{         sendError("MANIFEST_URL_ERROR");       }     }).bind(this),false);