gecko-dev/dom/xhr/XMLHttpRequestString.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 mozilla_dom_XMLHttpRequestString_h
#define mozilla_dom_XMLHttpRequestString_h

#include "mozilla/Mutex.h"
#include "nsString.h"

struct JSContext;
class JSString;

namespace mozilla::dom {

class ArrayBufferBuilder;
class BlobImpl;
class DOMString;
class XMLHttpRequestStringBuffer;
class XMLHttpRequestStringSnapshot;
class XMLHttpRequestStringWriterHelper;

// We want to avoid the dup of strings when XHR in workers has access to
// responseText for events dispatched during the loading state. For this reason
// we use this class, able to create snapshots of the current size of itself
// without making extra copies.
class XMLHttpRequestString final {
  friend class XMLHttpRequestStringWriterHelper;

 public:
  XMLHttpRequestString();
  ~XMLHttpRequestString();

  void Truncate();

  uint32_t Length() const;

  void Append(const nsAString& aString);

  // This method should be called only when the string is really needed because
  // it can cause the duplication of the strings in case the loading of the XHR
  // is not completed yet.
  [[nodiscard]] bool GetAsString(nsAString& aString) const;

  size_t SizeOfThis(MallocSizeOf aMallocSizeOf) const;

  const char16_t* Data() const;

  bool IsEmpty() const;

  void CreateSnapshot(XMLHttpRequestStringSnapshot& aSnapshot);

 private:
  XMLHttpRequestString(const XMLHttpRequestString&) = delete;
  XMLHttpRequestString& operator=(const XMLHttpRequestString&) = delete;
  XMLHttpRequestString& operator=(const XMLHttpRequestString&&) = delete;

  RefPtr<XMLHttpRequestStringBuffer> mBuffer;
};

// This class locks the buffer and allows the callee to write data into it.
class MOZ_STACK_CLASS XMLHttpRequestStringWriterHelper final {
 public:
  explicit XMLHttpRequestStringWriterHelper(XMLHttpRequestString& aString);
  ~XMLHttpRequestStringWriterHelper();

  /**
   * The existing length of the string. Do not call during BulkWrite().
   */
  uint32_t Length() const;

  mozilla::Result<mozilla::BulkWriteHandle<char16_t>, nsresult> BulkWrite(
      uint32_t aCapacity);

 private:
  XMLHttpRequestStringWriterHelper(const XMLHttpRequestStringWriterHelper&) =
      delete;
  XMLHttpRequestStringWriterHelper& operator=(
      const XMLHttpRequestStringWriterHelper&) = delete;
  XMLHttpRequestStringWriterHelper& operator=(
      const XMLHttpRequestStringWriterHelper&&) = delete;

  RefPtr<XMLHttpRequestStringBuffer> mBuffer;
  MutexAutoLock mLock;
};

// This class is the internal XMLHttpRequestStringBuffer of the
// XMLHttpRequestString plus the current length. GetAsString will return the
// string with that particular length also if the XMLHttpRequestStringBuffer is
// grown in the meantime.
class XMLHttpRequestStringSnapshot final {
  friend class XMLHttpRequestStringBuffer;

 public:
  XMLHttpRequestStringSnapshot();
  ~XMLHttpRequestStringSnapshot();

  XMLHttpRequestStringSnapshot& operator=(const XMLHttpRequestStringSnapshot&) =
      delete;

  void Reset() { ResetInternal(false /* isVoid */); }

  void SetVoid() { ResetInternal(true /* isVoid */); }

  bool IsVoid() const { return mVoid; }

  bool IsEmpty() const { return !mLength; }

  [[nodiscard]] bool GetAsString(DOMString& aString) const;

  JSString* GetAsJSStringCopy(JSContext* aCx) const;

 private:
  XMLHttpRequestStringSnapshot(const XMLHttpRequestStringSnapshot&) = delete;
  XMLHttpRequestStringSnapshot& operator=(
      const XMLHttpRequestStringSnapshot&&) = delete;

  void Set(XMLHttpRequestStringBuffer* aBuffer, uint32_t aLength);

  void ResetInternal(bool aIsVoid);

  RefPtr<XMLHttpRequestStringBuffer> mBuffer;
  uint32_t mLength;
  bool mVoid;
};

}  // namespace mozilla::dom

#endif  // mozilla_dom_XMLHttpRequestString_h