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// Copyright 2021 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef INCLUDE_V8_CONTEXT_H_
#define INCLUDE_V8_CONTEXT_H_
#include <stdint.h>
#include <vector>
#include "v8-data.h" // NOLINT(build/include_directory)
#include "v8-local-handle.h" // NOLINT(build/include_directory)
#include "v8-maybe.h" // NOLINT(build/include_directory)
#include "v8-snapshot.h" // NOLINT(build/include_directory)
#include "v8config.h" // NOLINT(build/include_directory)
namespace v8 {
class Function;
class MicrotaskQueue;
class Object;
class ObjectTemplate;
class Value;
class String;
/**
* A container for extension names.
*/
class V8_EXPORT ExtensionConfiguration {
public:
ExtensionConfiguration() : name_count_(0), names_(nullptr) {}
ExtensionConfiguration(int name_count, const char* names[])
: name_count_(name_count), names_(names) {}
const char** begin() const { return &names_[0]; }
const char** end() const { return &names_[name_count_]; }
private:
const int name_count_;
const char** names_;
};
/**
* A sandboxed execution context with its own set of built-in objects
* and functions.
*/
class V8_EXPORT Context : public Data {
public:
/**
* Returns the global proxy object.
*
* Global proxy object is a thin wrapper whose prototype points to actual
* context's global object with the properties like Object, etc. This is done
* that way for security reasons (for more details see
* https://wiki.mozilla.org/Gecko:SplitWindow).
*
* Please note that changes to global proxy object prototype most probably
* would break VM---v8 expects only global object as a prototype of global
* proxy object.
*/
Local<Object> Global();
/**
* Detaches the global object from its context before
* the global object can be reused to create a new context.
*/
void DetachGlobal();
/**
* Creates a new context and returns a handle to the newly allocated
* context.
*
* \param isolate The isolate in which to create the context.
*
* \param extensions An optional extension configuration containing
* the extensions to be installed in the newly created context.
*
* \param global_template An optional object template from which the
* global object for the newly created context will be created.
*
* \param global_object An optional global object to be reused for
* the newly created context. This global object must have been
* created by a previous call to Context::New with the same global
* template. The state of the global object will be completely reset
* and only object identify will remain.
*/
static Local<Context> New(
Isolate* isolate, ExtensionConfiguration* extensions = nullptr,
MaybeLocal<ObjectTemplate> global_template = MaybeLocal<ObjectTemplate>(),
MaybeLocal<Value> global_object = MaybeLocal<Value>(),
DeserializeInternalFieldsCallback internal_fields_deserializer =
DeserializeInternalFieldsCallback(),
MicrotaskQueue* microtask_queue = nullptr);
/**
* Create a new context from a (non-default) context snapshot. There
* is no way to provide a global object template since we do not create
* a new global object from template, but we can reuse a global object.
*
* \param isolate See v8::Context::New.
*
* \param context_snapshot_index The index of the context snapshot to
* deserialize from. Use v8::Context::New for the default snapshot.
*
* \param embedder_fields_deserializer Optional callback to deserialize
* internal fields. It should match the SerializeInternalFieldCallback used
* to serialize.
*
* \param extensions See v8::Context::New.
*
* \param global_object See v8::Context::New.
*/
static MaybeLocal<Context> FromSnapshot(
Isolate* isolate, size_t context_snapshot_index,
DeserializeInternalFieldsCallback embedder_fields_deserializer =
DeserializeInternalFieldsCallback(),
ExtensionConfiguration* extensions = nullptr,
MaybeLocal<Value> global_object = MaybeLocal<Value>(),
MicrotaskQueue* microtask_queue = nullptr);
/**
* Returns an global object that isn't backed by an actual context.
*
* The global template needs to have access checks with handlers installed.
* If an existing global object is passed in, the global object is detached
* from its context.
*
* Note that this is different from a detached context where all accesses to
* the global proxy will fail. Instead, the access check handlers are invoked.
*
* It is also not possible to detach an object returned by this method.
* Instead, the access check handlers need to return nothing to achieve the
* same effect.
*
* It is possible, however, to create a new context from the global object
* returned by this method.
*/
static MaybeLocal<Object> NewRemoteContext(
Isolate* isolate, Local<ObjectTemplate> global_template,
MaybeLocal<Value> global_object = MaybeLocal<Value>());
/**
* Sets the security token for the context. To access an object in
* another context, the security tokens must match.
*/
void SetSecurityToken(Local<Value> token);
/** Restores the security token to the default value. */
void UseDefaultSecurityToken();
/** Returns the security token of this context.*/
Local<Value> GetSecurityToken();
/**
* Enter this context. After entering a context, all code compiled
* and run is compiled and run in this context. If another context
* is already entered, this old context is saved so it can be
* restored when the new context is exited.
*/
void Enter();
/**
* Exit this context. Exiting the current context restores the
* context that was in place when entering the current context.
*/
void Exit();
/**
* Delegate to help with Deep freezing embedder-specific objects (such as
* JSApiObjects) that can not be frozen natively.
*/
class DeepFreezeDelegate {
public:
/**
* Performs embedder-specific operations to freeze the provided embedder
* object. The provided object *will* be frozen by DeepFreeze after this
* function returns, so only embedder-specific objects need to be frozen.
* This function *may not* create new JS objects or perform JS allocations.
* Any v8 objects reachable from the provided embedder object that should
* also be considered for freezing should be added to the children_out
* parameter. Returns true if the operation completed successfully.
*/
virtual bool FreezeEmbedderObjectAndGetChildren(
Local<Object> obj, std::vector<Local<Object>>& children_out) = 0;
};
/**
* Attempts to recursively freeze all objects reachable from this context.
* Some objects (generators, iterators, non-const closures) can not be frozen
* and will cause this method to throw an error. An optional delegate can be
* provided to help freeze embedder-specific objects.
*
* Freezing occurs in two steps:
* 1. "Marking" where we iterate through all objects reachable by this
* context, accumulating a list of objects that need to be frozen and
* looking for objects that can't be frozen. This step is separated because
* it is more efficient when we can assume there is no garbage collection.
* 2. "Freezing" where we go through the list of objects and freezing them.
* This effectively requires copying them so it may trigger garbage
* collection.
*/
Maybe<void> DeepFreeze(DeepFreezeDelegate* delegate = nullptr);
/** Returns the isolate associated with a current context. */
Isolate* GetIsolate();
/** Returns the microtask queue associated with a current context. */
MicrotaskQueue* GetMicrotaskQueue();
/** Sets the microtask queue associated with the current context. */
void SetMicrotaskQueue(MicrotaskQueue* queue);
/**
* The field at kDebugIdIndex used to be reserved for the inspector.
* It now serves no purpose.
*/
enum EmbedderDataFields { kDebugIdIndex = 0 };
/**
* Return the number of fields allocated for embedder data.
*/
uint32_t GetNumberOfEmbedderDataFields();
/**
* Gets the embedder data with the given index, which must have been set by a
* previous call to SetEmbedderData with the same index.
*/
V8_INLINE Local<Value> GetEmbedderData(int index);
/**
* Gets the binding object used by V8 extras. Extra natives get a reference
* to this object and can use it to "export" functionality by adding
* properties. Extra natives can also "import" functionality by accessing
* properties added by the embedder using the V8 API.
*/
Local<Object> GetExtrasBindingObject();
/**
* Sets the embedder data with the given index, growing the data as
* needed. Note that index 0 currently has a special meaning for Chrome's
* debugger.
*/
void SetEmbedderData(int index, Local<Value> value);
/**
* Gets a 2-byte-aligned native pointer from the embedder data with the given
* index, which must have been set by a previous call to
* SetAlignedPointerInEmbedderData with the same index. Note that index 0
* currently has a special meaning for Chrome's debugger.
*/
V8_INLINE void* GetAlignedPointerFromEmbedderData(int index);
/**
* Sets a 2-byte-aligned native pointer in the embedder data with the given
* index, growing the data as needed. Note that index 0 currently has a
* special meaning for Chrome's debugger.
*/
void SetAlignedPointerInEmbedderData(int index, void* value);
/**
* Control whether code generation from strings is allowed. Calling
* this method with false will disable 'eval' and the 'Function'
* constructor for code running in this context. If 'eval' or the
* 'Function' constructor are used an exception will be thrown.
*
* If code generation from strings is not allowed the
* V8::AllowCodeGenerationFromStrings callback will be invoked if
* set before blocking the call to 'eval' or the 'Function'
* constructor. If that callback returns true, the call will be
* allowed, otherwise an exception will be thrown. If no callback is
* set an exception will be thrown.
*/
void AllowCodeGenerationFromStrings(bool allow);
/**
* Returns true if code generation from strings is allowed for the context.
* For more details see AllowCodeGenerationFromStrings(bool) documentation.
*/
bool IsCodeGenerationFromStringsAllowed() const;
/**
* Sets the error description for the exception that is thrown when
* code generation from strings is not allowed and 'eval' or the 'Function'
* constructor are called.
*/
void SetErrorMessageForCodeGenerationFromStrings(Local<String> message);
/**
* Sets the error description for the exception that is thrown when
* wasm code generation is not allowed.
*/
void SetErrorMessageForWasmCodeGeneration(Local<String> message);
/**
* Return data that was previously attached to the context snapshot via
* SnapshotCreator, and removes the reference to it.
* Repeated call with the same index returns an empty MaybeLocal.
*/
template <class T>
V8_INLINE MaybeLocal<T> GetDataFromSnapshotOnce(size_t index);
/**
* If callback is set, abort any attempt to execute JavaScript in this
* context, call the specified callback, and throw an exception.
* To unset abort, pass nullptr as callback.
*/
using AbortScriptExecutionCallback = void (*)(Isolate* isolate,
Local<Context> context);
void SetAbortScriptExecution(AbortScriptExecutionCallback callback);
/**
* Returns the value that was set or restored by
* SetContinuationPreservedEmbedderData(), if any.
*/
Local<Value> GetContinuationPreservedEmbedderData() const;
/**
* Sets a value that will be stored on continuations and reset while the
* continuation runs.
*/
void SetContinuationPreservedEmbedderData(Local<Value> context);
/**
* Set or clear hooks to be invoked for promise lifecycle operations.
* To clear a hook, set it to an empty v8::Function. Each function will
* receive the observed promise as the first argument. If a chaining
* operation is used on a promise, the init will additionally receive
* the parent promise as the second argument.
*/
void SetPromiseHooks(Local<Function> init_hook, Local<Function> before_hook,
Local<Function> after_hook,
Local<Function> resolve_hook);
bool HasTemplateLiteralObject(Local<Value> object);
/**
* Stack-allocated class which sets the execution context for all
* operations executed within a local scope.
*/
class V8_NODISCARD Scope {
public:
explicit V8_INLINE Scope(Local<Context> context) : context_(context) {
context_->Enter();
}
V8_INLINE ~Scope() { context_->Exit(); }
private:
Local<Context> context_;
};
/**
* Stack-allocated class to support the backup incumbent settings object
* stack.
* https://html.spec.whatwg.org/multipage/webappapis.html#backup-incumbent-settings-object-stack
*/
class V8_EXPORT V8_NODISCARD BackupIncumbentScope final {
public:
/**
* |backup_incumbent_context| is pushed onto the backup incumbent settings
* object stack.
*/
explicit BackupIncumbentScope(Local<Context> backup_incumbent_context);
~BackupIncumbentScope();
private:
friend class internal::Isolate;
uintptr_t JSStackComparableAddressPrivate() const {
return js_stack_comparable_address_;
}
Local<Context> backup_incumbent_context_;
uintptr_t js_stack_comparable_address_ = 0;
const BackupIncumbentScope* prev_ = nullptr;
};
V8_INLINE static Context* Cast(Data* data);
private:
friend class Value;
friend class Script;
friend class Object;
friend class Function;
static void CheckCast(Data* obj);
internal::Address* GetDataFromSnapshotOnce(size_t index);
Local<Value> SlowGetEmbedderData(int index);
void* SlowGetAlignedPointerFromEmbedderData(int index);
};
// --- Implementation ---
Local<Value> Context::GetEmbedderData(int index) {
#ifndef V8_ENABLE_CHECKS
using A = internal::Address;
using I = internal::Internals;
A ctx = *reinterpret_cast<const A*>(this);
A embedder_data =
I::ReadTaggedPointerField(ctx, I::kNativeContextEmbedderDataOffset);
int value_offset =
I::kEmbedderDataArrayHeaderSize + (I::kEmbedderDataSlotSize * index);
A value = I::ReadRawField<A>(embedder_data, value_offset);
#ifdef V8_COMPRESS_POINTERS
// We read the full pointer value and then decompress it in order to avoid
// dealing with potential endiannes issues.
value = I::DecompressTaggedField(embedder_data, static_cast<uint32_t>(value));
#endif
#ifdef V8_ENABLE_CONSERVATIVE_STACK_SCANNING
return Local<Value>(reinterpret_cast<Value*>(value));
#else
internal::Isolate* isolate = internal::IsolateFromNeverReadOnlySpaceObject(
*reinterpret_cast<A*>(this));
A* result = HandleScope::CreateHandle(isolate, value);
return Local<Value>(reinterpret_cast<Value*>(result));
#endif
#else
return SlowGetEmbedderData(index);
#endif
}
void* Context::GetAlignedPointerFromEmbedderData(int index) {
#if !defined(V8_ENABLE_CHECKS)
using A = internal::Address;
using I = internal::Internals;
A ctx = internal::ValueHelper::ValueAsAddress(this);
A embedder_data =
I::ReadTaggedPointerField(ctx, I::kNativeContextEmbedderDataOffset);
int value_offset = I::kEmbedderDataArrayHeaderSize +
(I::kEmbedderDataSlotSize * index) +
I::kEmbedderDataSlotExternalPointerOffset;
Isolate* isolate = I::GetIsolateForSandbox(ctx);
return reinterpret_cast<void*>(
I::ReadExternalPointerField<internal::kEmbedderDataSlotPayloadTag>(
isolate, embedder_data, value_offset));
#else
return SlowGetAlignedPointerFromEmbedderData(index);
#endif
}
template <class T>
MaybeLocal<T> Context::GetDataFromSnapshotOnce(size_t index) {
T* data = reinterpret_cast<T*>(GetDataFromSnapshotOnce(index));
if (data) internal::PerformCastCheck(data);
return Local<T>(data);
}
Context* Context::Cast(v8::Data* data) {
#ifdef V8_ENABLE_CHECKS
CheckCast(data);
#endif
return static_cast<Context*>(data);
}
} // namespace v8
#endif // INCLUDE_V8_CONTEXT_H_
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