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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* 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/. */
/*
* The context-wide source hook allows the source of scripts/functions to be
* discarded, if that source is constant and readily-reloadable if it's needed
* in the future.
*
* Ordinarily, functions and scripts store a copy of their underlying source, to
* support |Function.prototype.toString| and debuggers. Some scripts, however,
* might be constant and retrievable on demand -- perhaps burned into the binary
* or in a readonly file provided by the embedding. Why not just ask the
* embedding for a copy of the source?
*
* The context-wide |SourceHook| gives embedders a way to respond to these
* requests. The source of scripts/functions compiled with the compile option
* |JS::CompileOptions::setSourceIsLazy(true)| is eligible to be discarded.
* (The exact conditions under which source is discarded are unspecified.) *If*
* source is discarded, performing an operation that requires source uses the
* source hook to load the source.
*
* The source hook must return the *exact* same source for every call. (This is
* why the source hook is unsuitable for use with scripts loaded from the web:
* in general, their contents can change over time.) If the source hook doesn't
* return the exact same source, Very Bad Things may happen. (For example,
* previously-valid indexes into the source will no longer be coherent: they
* might index out of bounds, into the middle of multi-unit code points, &c.)
*
* These APIs are experimental because they shouldn't provide a per-*context*
* mechanism, rather something that's per-compilation.
*/
#ifndef js_experimental_SourceHook_h
#define js_experimental_SourceHook_h
#include "mozilla/UniquePtr.h" // mozilla::UniquePtr
#include <stddef.h> // size_t
#include "jstypes.h" // JS_FRIEND_API
struct JS_PUBLIC_API JSContext;
namespace js {
/**
* A class of objects that return source code on demand.
*
* When code is compiled with setSourceIsLazy(true), SpiderMonkey doesn't
* retain the source code (and doesn't do lazy bytecode generation). If we ever
* need the source code, say, in response to a call to Function.prototype.
* toSource or Debugger.Source.prototype.text, then we call the 'load' member
* function of the instance of this class that has hopefully been registered
* with the runtime, passing the code's URL, and hope that it will be able to
* find the source.
*/
class SourceHook {
public:
virtual ~SourceHook() = default;
/**
* Attempt to load the source for |filename|.
*
* On success, return true and store an owning pointer to the UTF-8 or UTF-16
* contents of the file in whichever of |twoByteSource| or |utf8Source| is
* non-null. (Exactly one of these will be non-null.) If the stored pointer
* is non-null, source was loaded and must be |js_free|'d when it's no longer
* needed. If the stored pointer is null, the JS engine will simply act as if
* source was unavailable, and users like |Function.prototype.toString| will
* produce fallback results, e.g. "[native code]".
*
* On failure, return false. The contents of whichever of |twoByteSource| or
* |utf8Source| was initially non-null are unspecified and must not be
* |js_free|'d.
*/
virtual bool load(JSContext* cx, const char* filename,
char16_t** twoByteSource, char** utf8Source,
size_t* length) = 0;
};
/**
* Have |cx| use |hook| to retrieve lazily-retrieved source code. See the
* comments for SourceHook. The context takes ownership of the hook, and
* will delete it when the context itself is deleted, or when a new hook is
* set.
*/
extern JS_FRIEND_API void SetSourceHook(JSContext* cx,
mozilla::UniquePtr<SourceHook> hook);
/** Remove |cx|'s source hook, and return it. The caller now owns the hook. */
extern JS_FRIEND_API mozilla::UniquePtr<SourceHook> ForgetSourceHook(
JSContext* cx);
} // namespace js
#endif // js_experimental_SourceHook_h
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