/* -*- 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 mozilla_dom_FakeString_h__ #define mozilla_dom_FakeString_h__ #include "nsString.h" #include "nsStringBuffer.h" #include "mozilla/RefPtr.h" namespace mozilla { namespace dom { namespace binding_detail { // A struct that has the same layout as an nsString but much faster // constructor and destructor behavior. FakeString uses inline storage // for small strings and a nsStringBuffer for longer strings. struct FakeString { FakeString() : mFlags(nsString::F_TERMINATED) { } ~FakeString() { if (mFlags & nsString::F_SHARED) { nsStringBuffer::FromData(mData)->Release(); } } void Rebind(const nsString::char_type* aData, nsString::size_type aLength) { MOZ_ASSERT(mFlags == nsString::F_TERMINATED); mData = const_cast<nsString::char_type*>(aData); mLength = aLength; } // Share aString's string buffer, if it has one; otherwise, make this string // depend upon aString's data. aString should outlive this instance of // FakeString. void ShareOrDependUpon(const nsAString& aString) { RefPtr<nsStringBuffer> sharedBuffer = nsStringBuffer::FromString(aString); if (!sharedBuffer) { Rebind(aString.Data(), aString.Length()); } else { AssignFromStringBuffer(sharedBuffer.forget()); mLength = aString.Length(); } } void Truncate() { MOZ_ASSERT(mFlags == nsString::F_TERMINATED); mData = nsString::char_traits::sEmptyBuffer; mLength = 0; } void SetIsVoid(bool aValue) { MOZ_ASSERT(aValue, "We don't support SetIsVoid(false) on FakeString!"); Truncate(); mFlags |= nsString::F_VOIDED; } const nsString::char_type* Data() const { return mData; } nsString::char_type* BeginWriting() { return mData; } nsString::size_type Length() const { return mLength; } // Reserve space to write aLength chars, not including null-terminator. bool SetLength(nsString::size_type aLength, mozilla::fallible_t const&) { // Use mInlineStorage for small strings. if (aLength < sInlineCapacity) { SetData(mInlineStorage); } else { RefPtr<nsStringBuffer> buf = nsStringBuffer::Alloc((aLength + 1) * sizeof(nsString::char_type)); if (MOZ_UNLIKELY(!buf)) { return false; } AssignFromStringBuffer(buf.forget()); } mLength = aLength; mData[mLength] = char16_t(0); return true; } // If this ever changes, change the corresponding code in the // Optional<nsAString> specialization as well. const nsAString* ToAStringPtr() const { return reinterpret_cast<const nsString*>(this); } operator const nsAString& () const { return *reinterpret_cast<const nsString*>(this); } private: nsAString* ToAStringPtr() { return reinterpret_cast<nsString*>(this); } nsString::char_type* mData; nsString::size_type mLength; uint32_t mFlags; static const size_t sInlineCapacity = 64; nsString::char_type mInlineStorage[sInlineCapacity]; FakeString(const FakeString& other) = delete; void operator=(const FakeString& other) = delete; void SetData(nsString::char_type* aData) { MOZ_ASSERT(mFlags == nsString::F_TERMINATED); mData = const_cast<nsString::char_type*>(aData); } void AssignFromStringBuffer(already_AddRefed<nsStringBuffer> aBuffer) { SetData(static_cast<nsString::char_type*>(aBuffer.take()->Data())); mFlags = nsString::F_SHARED | nsString::F_TERMINATED; } friend class NonNull<nsAString>; // A class to use for our static asserts to ensure our object layout // matches that of nsString. class StringAsserter; friend class StringAsserter; class StringAsserter : public nsString { public: static void StaticAsserts() { static_assert(offsetof(FakeString, mInlineStorage) == sizeof(nsString), "FakeString should include all nsString members"); static_assert(offsetof(FakeString, mData) == offsetof(StringAsserter, mData), "Offset of mData should match"); static_assert(offsetof(FakeString, mLength) == offsetof(StringAsserter, mLength), "Offset of mLength should match"); static_assert(offsetof(FakeString, mFlags) == offsetof(StringAsserter, mFlags), "Offset of mFlags should match"); } }; }; } // namespace binding_detail } // namespace dom } // namespace mozilla #endif /* mozilla_dom_FakeString_h__ */