import FIREFOX_52_6_0esr_RELEASE from mozilla-esr52 hg repo

dom/bindings/FakeString.h

@@ -0,0 +1,160 @@
+/* -*- 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__ */