FixedBufferOutputStream.h

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/* -*- 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_FixedBufferOutputStream_h

#define mozilla_FixedBufferOutputStream_h

#include <cstddef>

#include "mozilla/fallible.h"

#include "mozilla/Mutex.h"

#include "mozilla/Span.h"

#include "mozilla/UniquePtr.h"

#include "nsIOutputStream.h"

#include "nsStringFwd.h"

template <class T>

class RefPtr;

namespace mozilla {

class StreamBufferSink;

// An output stream so you can read your potentially-async input stream into

// a contiguous buffer using NS_AsyncCopy. Back when streams were more

// synchronous and people didn't know blocking I/O was bad, if you wanted to

// read a stream into a flat buffer, you could use NS_ReadInputStreamToString

// or NS_ReadInputStreamToBuffer.  But those don't work with async streams.

// This can be used to replace hand-rolled Read/AsyncWait() loops.  Because you

// specify the expected size up front, the buffer is pre-allocated so wasteful

// reallocations can be avoided.

class FixedBufferOutputStream final : public nsIOutputStream {

  template <typename T, typename... Args>

  friend RefPtr<T> MakeRefPtr(Args&&... aArgs);

 public:

  // Factory method to get a FixedBufferOutputStream by allocating a char buffer

  // with the given length.

  static RefPtr<FixedBufferOutputStream> Create(size_t aLength);

  // Factory method to get a FixedBufferOutputStream by allocating a char buffer

  // with the given length, fallible version.

  static RefPtr<FixedBufferOutputStream> Create(size_t aLength,

                                                const mozilla::fallible_t&);

  // Factory method to get a FixedBufferOutputStream from a preallocated char

  // buffer. The output stream doesn't take ownership of the char buffer, so the

  // char buffer must outlive the output stream (to avoid a use-after-free).

  static RefPtr<FixedBufferOutputStream> Create(mozilla::Span<char> aBuffer);

  // Factory method to get a FixedBufferOutputStream from an arbitrary

  // StreamBufferSink.

  static RefPtr<FixedBufferOutputStream> Create(

      UniquePtr<StreamBufferSink>&& aSink);

  nsDependentCSubstring WrittenData();

  NS_DECL_THREADSAFE_ISUPPORTS

  NS_DECL_NSIOUTPUTSTREAM

 private:

  explicit FixedBufferOutputStream(UniquePtr<StreamBufferSink>&& aSink);

  ~FixedBufferOutputStream() = default;

  const UniquePtr<StreamBufferSink> mSink;

  Mutex mMutex;

  size_t mOffset MOZ_GUARDED_BY(mMutex);

  bool mWriting MOZ_GUARDED_BY(mMutex);

  bool mClosed MOZ_GUARDED_BY(mMutex);

};

}  // namespace mozilla

#endif  // mozilla_FixedBufferOutputStream_h