gecko-dev/dom/base/ScriptSettings.h

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/* -*- 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 "nsCxPusher.h"
#include "MainThreadUtils.h"
#include "nsIGlobalObject.h"
#include "nsIPrincipal.h"
#include "mozilla/Maybe.h"
class nsIGlobalObject;
namespace mozilla {
namespace dom {
/*
* System-wide setup/teardown routines. Init and Destroy should be invoked
* once each, at startup and shutdown (respectively).
*/
void InitScriptSettings();
void DestroyScriptSettings();
// This mostly gets the entry global, but doesn't entirely match the spec in
// certain edge cases. It's good enough for some purposes, but not others. If
// you want to call this function, ping bholley and describe your use-case.
nsIGlobalObject* BrokenGetEntryGlobal();
// Note: We don't yet expose GetEntryGlobal, because in order for it to be
// correct, we first need to replace a bunch of explicit cx pushing in the
// browser with AutoEntryScript. But GetIncumbentGlobal is simpler, because it
// can mostly be inferred from the JS stack.
nsIGlobalObject* GetIncumbentGlobal();
// 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;
struct ScriptSettingsStackEntry {
nsCOMPtr<nsIGlobalObject> mGlobalObject;
bool mIsCandidateEntryPoint;
ScriptSettingsStackEntry(nsIGlobalObject *aGlobal, bool aCandidate)
: mGlobalObject(aGlobal)
, mIsCandidateEntryPoint(aCandidate)
{
MOZ_ASSERT(mGlobalObject);
MOZ_ASSERT(mGlobalObject->GetGlobalJSObject(),
"Must have an actual JS global for the duration on the stack");
MOZ_ASSERT(JS_IsGlobalObject(mGlobalObject->GetGlobalJSObject()),
"No outer windows allowed");
}
~ScriptSettingsStackEntry() {
// We must have an actual JS global for the entire time this is on the stack.
MOZ_ASSERT_IF(mGlobalObject, mGlobalObject->GetGlobalJSObject());
}
bool NoJSAPI() { return this == &NoJSAPISingleton; }
static ScriptSettingsStackEntry NoJSAPISingleton;
private:
ScriptSettingsStackEntry() : mGlobalObject(nullptr)
, mIsCandidateEntryPoint(true)
{}
};
/*
* 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. Its current duties are as-follows:
*
* * Grabbing an appropriate JSContext, and, on the main thread, pushing it onto
* the JSContext stack.
* * Entering a null compartment, so that the consumer is forced to select a
* compartment to enter before manipulating objects.
*
* 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 AutoJSAPI {
public:
// Public constructor for use when the base class is constructed as-is. It
// uses the SafeJSContext (or worker equivalent), and enters a null
// compartment.
AutoJSAPI();
JSContext* cx() const { return mCx; }
bool CxPusherIsStackTop() { return mCxPusher.ref().IsStackTop(); }
protected:
// Protected constructor, allowing subclasses to specify a particular cx to
// be used.
AutoJSAPI(JSContext *aCx, bool aIsMainThread, bool aSkipNullAC = false);
private:
mozilla::Maybe<AutoCxPusher> mCxPusher;
mozilla::Maybe<JSAutoNullCompartment> mNullAc;
JSContext *mCx;
};
// Note - the ideal way to implement this is with an accessor on AutoJSAPI
// that lets us select the error reporting target. But at present,
// implementing it that way would require us to destroy and reconstruct
// mCxPusher, which is pretty wasteful. So we do this for now, since it should
// be pretty easy to switch things over later.
//
// This should only be used on the main thread.
class AutoJSAPIWithErrorsReportedToWindow : public AutoJSAPI {
public:
AutoJSAPIWithErrorsReportedToWindow(nsIScriptContext* aScx);
};
/*
* A class that represents a new script entry point.
*/
class AutoEntryScript : public AutoJSAPI,
protected ScriptSettingsStackEntry {
public:
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:
JSAutoCompartment mAc;
dom::ScriptSettingsStack& mStack;
nsCOMPtr<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:
AutoIncumbentScript(nsIGlobalObject* aGlobalObject);
~AutoIncumbentScript();
private:
dom::ScriptSettingsStack& mStack;
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 {
public:
AutoNoJSAPI(bool aIsMainThread = NS_IsMainThread());
~AutoNoJSAPI();
private:
dom::ScriptSettingsStack& mStack;
mozilla::Maybe<AutoCxPusher> mCxPusher;
};
} // namespace dom
} // namespace mozilla
#endif // mozilla_dom_ScriptSettings_h