/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ // vim: ft=cpp tw=78 sw=2 et ts=2 /* This Source Code Form is subject to the terms of the Mozilla Public * License, v. 2.0. If a copy of the MPL was not distributed with this * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ /* Utilities for managing the script settings object stack defined in webapps */ #ifndef mozilla_dom_ScriptSettings_h #define mozilla_dom_ScriptSettings_h #include "MainThreadUtils.h" #include "nsIGlobalObject.h" #include "nsIPrincipal.h" #include "mozilla/Maybe.h" #include "jsapi.h" class nsPIDOMWindow; class nsGlobalWindow; class nsIScriptContext; class nsIDocument; namespace mozilla { namespace dom { // For internal use only - use AutoJSAPI instead. namespace danger { /** * Fundamental cx pushing class. All other cx pushing classes are implemented * in terms of this class. */ class MOZ_STACK_CLASS AutoCxPusher { public: explicit AutoCxPusher(JSContext *aCx, bool aAllowNull = false); ~AutoCxPusher(); nsIScriptContext* GetScriptContext() { return mScx; } // Returns true if this AutoCxPusher performed the push that is currently at // the top of the cx stack. bool IsStackTop() const; private: mozilla::Maybe mAutoRequest; nsCOMPtr mScx; uint32_t mStackDepthAfterPush; #ifdef DEBUG JSContext* mPushedContext; unsigned mCompartmentDepthOnEntry; #endif }; } /* namespace danger */ /* * System-wide setup/teardown routines. Init and Destroy should be invoked * once each, at startup and shutdown (respectively). */ void InitScriptSettings(); void DestroyScriptSettings(); // To implement a web-compatible browser, it is often necessary to obtain the // global object that is "associated" with the currently-running code. This // process is made more complicated by the fact that, historically, different // algorithms have operated with different definitions of the "associated" // global. // // HTML5 formalizes this into two concepts: the "incumbent global" and the // "entry global". The incumbent global corresponds to the global of the // current script being executed, whereas the entry global corresponds to the // global of the script where the current JS execution began. // // There is also a potentially-distinct third global that is determined by the // current compartment. This roughly corresponds with the notion of Realms in // ECMAScript. // // Suppose some event triggers an event listener in window |A|, which invokes a // scripted function in window |B|, which invokes the |window.location.href| // setter in window |C|. The entry global would be |A|, the incumbent global // would be |B|, and the current compartment would be that of |C|. // // In general, it's best to use to use the most-closely-associated global // unless the spec says to do otherwise. In 95% of the cases, the global of // the current compartment (GetCurrentGlobal()) is the right thing. For // example, WebIDL constructors (new C.XMLHttpRequest()) are initialized with // the global of the current compartment (i.e. |C|). // // The incumbent global is very similar, but differs in a few edge cases. For // example, if window |B| does |C.location.href = "..."|, the incumbent global // used for the navigation algorithm is B, because no script from |C| was ever run. // // The entry global is used for various things like computing base URIs, mostly // for historical reasons. // // Note that all of these functions return bonafide global objects. This means // that, for Windows, they always return the inner. // Returns the global associated with the top-most Candidate Entry Point on // the Script Settings Stack. See the HTML spec. This may be null. nsIGlobalObject* GetEntryGlobal(); // If the entry global is a window, returns its extant document. Otherwise, // returns null. nsIDocument* GetEntryDocument(); // Returns the global associated with the top-most entry of the the Script // Settings Stack. See the HTML spec. This may be null. nsIGlobalObject* GetIncumbentGlobal(); // Returns the global associated with the current compartment. This may be null. nsIGlobalObject* GetCurrentGlobal(); // JS-implemented WebIDL presents an interesting situation with respect to the // subject principal. A regular C++-implemented API can simply examine the // compartment of the most-recently-executed script, and use that to infer the // responsible party. However, JS-implemented APIs are run with system // principal, and thus clobber the subject principal of the script that // invoked the API. So we have to do some extra work to keep track of this // information. // // We therefore implement the following behavior: // * Each Script Settings Object has an optional WebIDL Caller Principal field. // This defaults to null. // * When we push an Entry Point in preparation to run a JS-implemented WebIDL // callback, we grab the subject principal at the time of invocation, and // store that as the WebIDL Caller Principal. // * When non-null, callers can query this principal from script via an API on // Components.utils. nsIPrincipal* GetWebIDLCallerPrincipal(); // This may be used by callers that know that their incumbent global is non- // null (i.e. they know there have been no System Caller pushes since the // inner-most script execution). inline JSObject& IncumbentJSGlobal() { return *GetIncumbentGlobal()->GetGlobalJSObject(); } class ScriptSettingsStack; class ScriptSettingsStackEntry { friend class ScriptSettingsStack; public: ~ScriptSettingsStackEntry(); bool NoJSAPI() { return !mGlobalObject; } protected: ScriptSettingsStackEntry(nsIGlobalObject *aGlobal, bool aCandidate); nsCOMPtr mGlobalObject; bool mIsCandidateEntryPoint; private: // This constructor is only for use by AutoNoJSAPI. friend class AutoNoJSAPI; ScriptSettingsStackEntry(); ScriptSettingsStackEntry *mOlder; }; /* * For any interaction with JSAPI, an AutoJSAPI (or one of its subclasses) * must be on the stack. * * This base class should be instantiated as-is when the caller wants to use * JSAPI but doesn't expect to run script. The caller must then call one of its * Init functions before being able to access the JSContext through cx(). * Its current duties are as-follows (see individual Init comments for details): * * * Grabbing an appropriate JSContext, and, on the main thread, pushing it onto * the JSContext stack. * * Entering an initial (possibly null) compartment, to ensure that the * previously entered compartment for that JSContext is not used by mistake. * * Additionally, the following duties are planned, but not yet implemented: * * * De-poisoning the JSRuntime to allow manipulation of JSAPI. We can't * actually implement this poisoning until all the JSContext pushing in the * system goes through AutoJSAPI (see bug 951991). For now, this de-poisoning * effectively corresponds to having a non-null cx on the stack. * * Reporting any exceptions left on the JSRuntime, unless the caller steals * or silences them. * * Entering a JSAutoRequest. At present, this is handled by the cx pushing * on the main thread, and by other code on workers. Depending on the order * in which various cleanup lands, this may never be necessary, because * JSAutoRequests may go away. * * In situations where the consumer expects to run script, AutoEntryScript * should be used, which does additional manipulation of the script settings * stack. In bug 991758, we'll add hard invariants to SpiderMonkey, such that * any attempt to run script without an AutoEntryScript on the stack will * fail. This prevents system code from accidentally triggering script * execution at inopportune moments via surreptitious getters and proxies. */ class MOZ_STACK_CLASS AutoJSAPI { public: // Trivial constructor. One of the Init functions must be called before // accessing the JSContext through cx(). AutoJSAPI(); // This uses the SafeJSContext (or worker equivalent), and enters a null // compartment, so that the consumer is forced to select a compartment to // enter before manipulating objects. void Init(); // This uses the SafeJSContext (or worker equivalent), and enters the // compartment of aGlobalObject. // If aGlobalObject or its associated JS global are null then it returns // false and use of cx() will cause an assertion. bool Init(nsIGlobalObject* aGlobalObject); // Unsurprisingly, this uses aCx and enters the compartment of aGlobalObject. // If aGlobalObject or its associated JS global are null then it returns // false and use of cx() will cause an assertion. // If aCx is null it will cause an assertion. bool Init(nsIGlobalObject* aGlobalObject, JSContext* aCx); // This may only be used on the main thread. // This attempts to use the JSContext associated with aGlobalObject, otherwise // it uses the SafeJSContext. It then enters the compartment of aGlobalObject. // This means that existing error reporting mechanisms that use the JSContext // to find the JSErrorReporter should still work as before. // We should be able to remove this around bug 981198. // If aGlobalObject or its associated JS global are null then it returns // false and use of cx() will cause an assertion. bool InitWithLegacyErrorReporting(nsIGlobalObject* aGlobalObject); // Convenience functions to take an nsPIDOMWindow* or nsGlobalWindow*, // when it is more easily available than an nsIGlobalObject. bool Init(nsPIDOMWindow* aWindow); bool Init(nsPIDOMWindow* aWindow, JSContext* aCx); bool Init(nsGlobalWindow* aWindow); bool Init(nsGlobalWindow* aWindow, JSContext* aCx); bool InitWithLegacyErrorReporting(nsPIDOMWindow* aWindow); bool InitWithLegacyErrorReporting(nsGlobalWindow* aWindow); JSContext* cx() const { MOZ_ASSERT(mCx, "Must call Init before using an AutoJSAPI"); MOZ_ASSERT_IF(NS_IsMainThread(), CxPusherIsStackTop()); return mCx; } bool CxPusherIsStackTop() const { return mCxPusher->IsStackTop(); } protected: // Protected constructor, allowing subclasses to specify a particular cx to // be used. This constructor initialises the AutoJSAPI, so Init must NOT be // called on subclasses that use this. // If aGlobalObject, its associated JS global or aCx are null this will cause // an assertion, as will setting aIsMainThread incorrectly. AutoJSAPI(nsIGlobalObject* aGlobalObject, bool aIsMainThread, JSContext* aCx); private: mozilla::Maybe mCxPusher; mozilla::Maybe mAutoNullableCompartment; JSContext *mCx; void InitInternal(JSObject* aGlobal, JSContext* aCx, bool aIsMainThread); }; /* * A class that represents a new script entry point. */ class AutoEntryScript : public AutoJSAPI, protected ScriptSettingsStackEntry { public: explicit AutoEntryScript(nsIGlobalObject* aGlobalObject, bool aIsMainThread = NS_IsMainThread(), // Note: aCx is mandatory off-main-thread. JSContext* aCx = nullptr); ~AutoEntryScript(); void SetWebIDLCallerPrincipal(nsIPrincipal *aPrincipal) { mWebIDLCallerPrincipal = aPrincipal; } private: // It's safe to make this a weak pointer, since it's the subject principal // when we go on the stack, so can't go away until after we're gone. In // particular, this is only used from the CallSetup constructor, and only in // the aIsJSImplementedWebIDL case. And in that case, the subject principal // is the principal of the callee function that is part of the CallArgs just a // bit up the stack, and which will outlive us. So we know the principal // can't go away until then either. nsIPrincipal* mWebIDLCallerPrincipal; friend nsIPrincipal* GetWebIDLCallerPrincipal(); }; /* * A class that can be used to force a particular incumbent script on the stack. */ class AutoIncumbentScript : protected ScriptSettingsStackEntry { public: explicit AutoIncumbentScript(nsIGlobalObject* aGlobalObject); private: JS::AutoHideScriptedCaller mCallerOverride; }; /* * A class to put the JS engine in an unusable state. The subject principal * will become System, the information on the script settings stack is * rendered inaccessible, and JSAPI may not be manipulated until the class is * either popped or an AutoJSAPI instance is subsequently pushed. * * This class may not be instantiated if an exception is pending. */ class AutoNoJSAPI : protected ScriptSettingsStackEntry { public: explicit AutoNoJSAPI(bool aIsMainThread = NS_IsMainThread()); private: mozilla::Maybe mCxPusher; }; } // namespace dom /** * Use AutoJSContext when you need a JS context on the stack but don't have one * passed as a parameter. AutoJSContext will take care of finding the most * appropriate JS context and release it when leaving the stack. */ class MOZ_STACK_CLASS AutoJSContext { public: explicit AutoJSContext(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM); operator JSContext*() const; protected: explicit AutoJSContext(bool aSafe MOZ_GUARD_OBJECT_NOTIFIER_PARAM); // We need this Init() method because we can't use delegating constructor for // the moment. It is a C++11 feature and we do not require C++11 to be // supported to be able to compile Gecko. void Init(bool aSafe MOZ_GUARD_OBJECT_NOTIFIER_PARAM); JSContext* mCx; dom::AutoJSAPI mJSAPI; MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER }; /** * Use ThreadsafeAutoJSContext when you want an AutoJSContext but might be * running on a worker thread. */ class MOZ_STACK_CLASS ThreadsafeAutoJSContext { public: explicit ThreadsafeAutoJSContext(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM); operator JSContext*() const; private: JSContext* mCx; // Used on workers. Null means mainthread. Maybe mRequest; // Used on workers. Maybe mAutoJSContext; // Used on main thread. MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER }; /** * AutoSafeJSContext is similar to AutoJSContext but will only return the safe * JS context. That means it will never call nsContentUtils::GetCurrentJSContext(). * * Note - This is deprecated. Please use AutoJSAPI instead. */ class MOZ_STACK_CLASS AutoSafeJSContext : public AutoJSContext { public: explicit AutoSafeJSContext(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM); private: JSAutoCompartment mAc; }; /** * Like AutoSafeJSContext but can be used safely on worker threads. */ class MOZ_STACK_CLASS ThreadsafeAutoSafeJSContext { public: explicit ThreadsafeAutoSafeJSContext(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM); operator JSContext*() const; private: JSContext* mCx; // Used on workers. Null means mainthread. Maybe mRequest; // Used on workers. Maybe mAutoSafeJSContext; // Used on main thread. MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER }; } // namespace mozilla #endif // mozilla_dom_ScriptSettings_h