gecko-dev/dom/base/nsJSUtils.h

/* -*- 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/. */

#ifndef nsJSUtils_h__
#define nsJSUtils_h__

/**
 * This is not a generated file. It contains common utility functions
 * invoked from the JavaScript code generated from IDL interfaces.
 * The goal of the utility functions is to cut down on the size of
 * the generated code itself.
 */

#include "mozilla/Assertions.h"

#include "jsapi.h"
#include "js/CompileOptions.h"
#include "js/Conversions.h"
#include "js/String.h"  // JS::{,Lossy}CopyLinearStringChars, JS::CopyStringChars, JS::Get{,Linear}StringLength, JS::MaxStringLength, JS::StringHasLatin1Chars
#include "js/Utility.h"  // JS::FreePolicy
#include "nsString.h"
#include "xpcpublic.h"

class nsIScriptContext;
class nsIScriptElement;
class nsIScriptGlobalObject;
class nsXBLPrototypeBinding;

namespace mozilla {
union Utf8Unit;

namespace dom {
class AutoJSAPI;
class Element;
}  // namespace dom
}  // namespace mozilla

class nsJSUtils {
 public:
  /**
   * Retrieve the inner window ID based on the given JSContext.
   *
   * @param JSContext aContext
   *        The JSContext from which you want to find the inner window ID.
   *
   * @returns uint64_t the inner window ID.
   */
  static uint64_t GetCurrentlyRunningCodeInnerWindowID(JSContext* aContext);

  static nsresult CompileFunction(mozilla::dom::AutoJSAPI& jsapi,
                                  JS::HandleVector<JSObject*> aScopeChain,
                                  JS::CompileOptions& aOptions,
                                  const nsACString& aName, uint32_t aArgCount,
                                  const char** aArgArray,
                                  const nsAString& aBody,
                                  JSObject** aFunctionObject);

  static nsresult UpdateFunctionDebugMetadata(
      mozilla::dom::AutoJSAPI& jsapi, JS::Handle<JSObject*> aFun,
      JS::CompileOptions& aOptions, JS::Handle<JSString*> aElementAttributeName,
      JS::Handle<JS::Value> aPrivateValue);

  static bool IsScriptable(JS::Handle<JSObject*> aEvaluationGlobal);

  // Returns false if an exception got thrown on aCx.  Passing a null
  // aElement is allowed; that wil produce an empty aScopeChain.
  static bool GetScopeChainForElement(
      JSContext* aCx, mozilla::dom::Element* aElement,
      JS::MutableHandleVector<JSObject*> aScopeChain);

  static void ResetTimeZone();

  static bool DumpEnabled();

  // A helper function that receives buffer pointer, creates ArrayBuffer, and
  // convert it to Uint8Array.
  // Note that the buffer needs to be created by JS_malloc (or at least can be
  // freed by JS_free), as the resulting Uint8Array takes the ownership of the
  // buffer.
  static JSObject* MoveBufferAsUint8Array(
      JSContext* aCx, size_t aSize,
      mozilla::UniquePtr<uint8_t[], JS::FreePolicy> aBuffer);
};

template <typename T, typename std::enable_if_t<std::is_same<
                          typename T::char_type, char16_t>::value>* = nullptr>
inline bool AssignJSString(JSContext* cx, T& dest, JSString* s) {
  size_t len = JS::GetStringLength(s);
  static_assert(JS::MaxStringLength < (1 << 30),
                "Shouldn't overflow here or in SetCapacity");

  if (XPCStringConvert::MaybeAssignUCStringChars(s, len, dest)) {
    return true;
  }

  // We don't bother checking for a dynamic-atom external string, because we'd
  // just need to copy out of it anyway.

  if (MOZ_UNLIKELY(!dest.SetLength(len, mozilla::fallible))) {
    JS_ReportOutOfMemory(cx);
    return false;
  }
  return JS::CopyStringChars(cx, dest.BeginWriting(), s, len);
}

// Specialization for UTF8String.
template <typename T, typename std::enable_if_t<std::is_same<
                          typename T::char_type, char>::value>* = nullptr>
inline bool AssignJSString(JSContext* cx, T& dest, JSString* s) {
  using namespace mozilla;
  CheckedInt<size_t> bufLen(JS::GetStringLength(s));

  if (XPCStringConvert::MaybeAssignUTF8StringChars(s, bufLen.value(), dest)) {
    return true;
  }

  // From the contract for JS_EncodeStringToUTF8BufferPartial, to guarantee that
  // the whole string is converted.
  if (JS::StringHasLatin1Chars(s)) {
    bufLen *= 2;
  } else {
    bufLen *= 3;
  }

  if (MOZ_UNLIKELY(!bufLen.isValid())) {
    JS_ReportOutOfMemory(cx);
    return false;
  }

  // Shouldn't really matter, but worth being safe.
  const bool kAllowShrinking = true;

  auto handleOrErr = dest.BulkWrite(bufLen.value(), 0, kAllowShrinking);
  if (MOZ_UNLIKELY(handleOrErr.isErr())) {
    JS_ReportOutOfMemory(cx);
    return false;
  }

  auto handle = handleOrErr.unwrap();

  auto maybe = JS_EncodeStringToUTF8BufferPartial(cx, s, handle.AsSpan());
  if (MOZ_UNLIKELY(!maybe)) {
    JS_ReportOutOfMemory(cx);
    return false;
  }

  size_t read;
  size_t written;
  std::tie(read, written) = *maybe;

  MOZ_ASSERT(read == JS::GetStringLength(s));
  handle.Finish(written, kAllowShrinking);
  return true;
}

inline void AssignJSLinearString(nsAString& dest, JSLinearString* s) {
  size_t len = JS::GetLinearStringLength(s);
  static_assert(JS::MaxStringLength < (1 << 30),
                "Shouldn't overflow here or in SetCapacity");
  dest.SetLength(len);
  JS::CopyLinearStringChars(dest.BeginWriting(), s, len);
}

inline void AssignJSLinearString(nsACString& dest, JSLinearString* s) {
  size_t len = JS::GetLinearStringLength(s);
  static_assert(JS::MaxStringLength < (1 << 30),
                "Shouldn't overflow here or in SetCapacity");
  dest.SetLength(len);
  JS::LossyCopyLinearStringChars(dest.BeginWriting(), s, len);
}

template <typename T>
class nsTAutoJSLinearString : public nsTAutoString<T> {
 public:
  explicit nsTAutoJSLinearString(JSLinearString* str) {
    AssignJSLinearString(*this, str);
  }
};

using nsAutoJSLinearString = nsTAutoJSLinearString<char16_t>;
using nsAutoJSLinearCString = nsTAutoJSLinearString<char>;

template <typename T>
class nsTAutoJSString : public nsTAutoString<T> {
 public:
  /**
   * nsTAutoJSString should be default constructed, which leaves it empty
   * (this->IsEmpty()), and initialized with one of the init() methods below.
   */
  nsTAutoJSString() = default;

  bool init(JSContext* aContext, JSString* str) {
    return AssignJSString(aContext, *this, str);
  }

  bool init(JSContext* aContext, const JS::Value& v) {
    if (v.isString()) {
      return init(aContext, v.toString());
    }

    // Stringify, making sure not to run script.
    JS::Rooted<JSString*> str(aContext);
    if (v.isObject()) {
      str = JS_NewStringCopyZ(aContext, "[Object]");
    } else {
      JS::Rooted<JS::Value> rootedVal(aContext, v);
      str = JS::ToString(aContext, rootedVal);
    }

    return str && init(aContext, str);
  }

  bool init(JSContext* aContext, jsid id) {
    JS::Rooted<JS::Value> v(aContext);
    return JS_IdToValue(aContext, id, &v) && init(aContext, v);
  }

  bool init(const JS::Value& v);

  ~nsTAutoJSString() = default;
};

using nsAutoJSString = nsTAutoJSString<char16_t>;

// Note that this is guaranteed to be UTF-8.
using nsAutoJSCString = nsTAutoJSString<char>;

#endif /* nsJSUtils_h__ */