Bug 1791725 - Add FixedBufferOutputStream; r=xpcom-reviewers,nika

Differential Revision: https://phabricator.services.mozilla.com/D157790

xpcom/io/FixedBufferOutputStream.cpp

+/* -*- 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/. */
+
+#include "FixedBufferOutputStream.h"
+
+#include "mozilla/RefPtr.h"
+#include "mozilla/StreamBufferSinkImpl.h"
+#include "nsStreamUtils.h"
+#include "nsString.h"
+
+namespace mozilla {
+
+FixedBufferOutputStream::FixedBufferOutputStream(
+    UniquePtr<StreamBufferSink>&& aSink)
+    : mSink(std::move(aSink)),
+      mMutex("FixedBufferOutputStream::mMutex"),
+      mOffset(0),
+      mWriting(false),
+      mClosed(false) {}
+
+// static
+RefPtr<FixedBufferOutputStream> FixedBufferOutputStream::Create(
+    size_t aLength) {
+  MOZ_ASSERT(aLength);
+
+  return MakeRefPtr<FixedBufferOutputStream>(MakeUnique<BufferSink>(aLength));
+}
+
+// static
+RefPtr<FixedBufferOutputStream> FixedBufferOutputStream::Create(
+    size_t aLength, const mozilla::fallible_t&) {
+  MOZ_ASSERT(aLength);
+
+  auto sink = BufferSink::Alloc(aLength);
+
+  if (NS_WARN_IF(!sink)) {
+    return nullptr;
+  }
+
+  return MakeRefPtr<FixedBufferOutputStream>(std::move(sink));
+}
+
+// static
+RefPtr<FixedBufferOutputStream> FixedBufferOutputStream::Create(
+    mozilla::Span<char> aBuffer) {
+  return MakeRefPtr<FixedBufferOutputStream>(
+      MakeUnique<nsBorrowedSink>(aBuffer));
+}
+
+// static
+RefPtr<FixedBufferOutputStream> FixedBufferOutputStream::Create(
+    UniquePtr<StreamBufferSink>&& aSink) {
+  return MakeRefPtr<FixedBufferOutputStream>(std::move(aSink));
+}
+
+nsDependentCSubstring FixedBufferOutputStream::WrittenData() {
+  MutexAutoLock autoLock(mMutex);
+
+  return mSink->Slice(mOffset);
+}
+
+NS_IMPL_ISUPPORTS(FixedBufferOutputStream, nsIOutputStream)
+
+NS_IMETHODIMP
+FixedBufferOutputStream::Close() {
+  MutexAutoLock autoLock(mMutex);
+
+  if (mWriting) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  mClosed = true;
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+FixedBufferOutputStream::Flush() { return NS_OK; }
+
+NS_IMETHODIMP
+FixedBufferOutputStream::Write(const char* aBuf, uint32_t aCount,
+                               uint32_t* _retval) {
+  return WriteSegments(NS_CopyBufferToSegment, const_cast<char*>(aBuf), aCount,
+                       _retval);
+}
+
+NS_IMETHODIMP
+FixedBufferOutputStream::WriteFrom(nsIInputStream* aFromStream, uint32_t aCount,
+                                   uint32_t* _retval) {
+  return WriteSegments(NS_CopyStreamToSegment, aFromStream, aCount, _retval);
+}
+
+NS_IMETHODIMP
+FixedBufferOutputStream::WriteSegments(nsReadSegmentFun aReader, void* aClosure,
+                                       uint32_t aCount, uint32_t* _retval) {
+  MOZ_ASSERT(_retval);
+
+  MutexAutoLock autoLock(mMutex);
+
+  if (mWriting) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  if (mClosed) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+
+  size_t length = mSink->Data().Length();
+  size_t offset = mOffset;
+
+  MOZ_ASSERT(length >= offset, "Bad stream state!");
+
+  size_t maxCount = length - offset;
+  if (maxCount == 0) {
+    *_retval = 0;
+    return NS_OK;
+  }
+
+  if (aCount > maxCount) {
+    aCount = maxCount;
+  }
+
+  mWriting = true;
+
+  nsresult rv;
+
+  {
+    MutexAutoUnlock autoUnlock(mMutex);
+
+    rv = aReader(this, aClosure, mSink->Data().Elements() + offset, 0, aCount,
+                 _retval);
+  }
+
+  mWriting = false;
+
+  if (NS_SUCCEEDED(rv)) {
+    MOZ_ASSERT(*_retval <= aCount,
+               "Reader should not read more than we asked it to read!");
+    mOffset += *_retval;
+  }
+
+  // As defined in nsIOutputStream.idl, do not pass reader func errors.
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+FixedBufferOutputStream::IsNonBlocking(bool* _retval) {
+  *_retval = true;
+  return NS_OK;
+}
+
+}  // namespace mozilla

xpcom/io/FixedBufferOutputStream.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_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

xpcom/io/StreamBufferSink.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_StreamBufferSink_h
+#define mozilla_StreamBufferSink_h
+
+#include <cstddef>
+#include "mozilla/Span.h"
+#include "nsString.h"
+
+namespace mozilla {
+
+class StreamBufferSink {
+ public:
+  virtual mozilla::Span<char> Data() = 0;
+
+  nsDependentCSubstring Slice(size_t aOffset) {
+    return nsDependentCSubstring(Data().First(aOffset));
+  }
+
+  virtual ~StreamBufferSink() = default;
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_StreamBufferSink_h

xpcom/io/StreamBufferSinkImpl.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_StreamBufferSinkImpl_h
+#define mozilla_StreamBufferSinkImpl_h
+
+#include "mozilla/Buffer.h"
+#include "mozilla/StreamBufferSink.h"
+#include "mozilla/UniquePtr.h"
+
+namespace mozilla {
+
+class BufferSink final : public StreamBufferSink {
+ public:
+  explicit BufferSink(Buffer<char>&& aBuffer) : mBuffer(std::move(aBuffer)) {}
+
+  explicit BufferSink(size_t aLength) : mBuffer(aLength) {}
+
+  static UniquePtr<BufferSink> Alloc(size_t aLength) {
+    auto maybeBuffer = Buffer<char>::Alloc(aLength);
+    if (!maybeBuffer) {
+      return nullptr;
+    }
+
+    return MakeUnique<BufferSink>(maybeBuffer.extract());
+  }
+
+  mozilla::Span<char> Data() override { return mBuffer.AsWritableSpan(); }
+
+ private:
+  Buffer<char> mBuffer;
+};
+
+class nsBorrowedSink final : public StreamBufferSink {
+ public:
+  explicit nsBorrowedSink(mozilla::Span<char> aBuffer) : mBuffer(aBuffer) {}
+
+  mozilla::Span<char> Data() override { return mBuffer; }
+
+ private:
+  mozilla::Span<char> mBuffer;
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_StreamBufferSinkImpl_h

xpcom/io/moz.build

@@ -92,6 +92,7 @@ EXPORTS += [
 EXPORTS.mozilla += [
     "Base64.h",
     "FilePreferences.h",
+    "FixedBufferOutputStream.h",
     "InputStreamLengthHelper.h",
     "InputStreamLengthWrapper.h",
     "NonBlockingAsyncInputStream.h",
@@ -99,6 +100,8 @@ EXPORTS.mozilla += [
     "SnappyCompressOutputStream.h",
     "SnappyFrameUtils.h",
     "SnappyUncompressInputStream.h",
+    "StreamBufferSink.h",
+    "StreamBufferSinkImpl.h",
     "StreamBufferSource.h",
 ]
 
@@ -107,6 +110,7 @@ UNIFIED_SOURCES += [
     "crc32c.c",
     "FileDescriptorFile.cpp",
     "FilePreferences.cpp",
+    "FixedBufferOutputStream.cpp",
     "InputStreamLengthHelper.cpp",
     "InputStreamLengthWrapper.cpp",
     "NonBlockingAsyncInputStream.cpp",