fune/xpcom/io/nsBinaryStream.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/. */

/**
 * This file contains implementations of the nsIBinaryInputStream and
 * nsIBinaryOutputStream interfaces.  Together, these interfaces allows reading
 * and writing of primitive data types (integers, floating-point values,
 * booleans, etc.) to a stream in a binary, untagged, fixed-endianness format.
 * This might be used, for example, to implement network protocols or to
 * produce architecture-neutral binary disk files, i.e. ones that can be read
 * and written by both big-endian and little-endian platforms.  Output is
 * written in big-endian order (high-order byte first), as this is traditional
 * network order.
 *
 * @See nsIBinaryInputStream
 * @See nsIBinaryOutputStream
 */
#include <algorithm>
#include <string.h>

#include "nsBinaryStream.h"

#include "mozilla/EndianUtils.h"
#include "mozilla/PodOperations.h"
#include "mozilla/RefPtr.h"
#include "mozilla/Span.h"
#include "mozilla/UniquePtr.h"

#include "nsCRT.h"
#include "nsString.h"
#include "nsISerializable.h"
#include "nsIClassInfo.h"
#include "nsComponentManagerUtils.h"
#include "nsIURI.h"       // for NS_IURI_IID
#include "nsIX509Cert.h"  // for NS_IX509CERT_IID

#include "js/ArrayBuffer.h"  // JS::{GetArrayBuffer{,ByteLength},IsArrayBufferObject}
#include "js/GCAPI.h"        // JS::AutoCheckCannotGC
#include "js/RootingAPI.h"  // JS::{Handle,Rooted}
#include "js/Value.h"       // JS::Value

using mozilla::AsBytes;
using mozilla::MakeUnique;
using mozilla::PodCopy;
using mozilla::Span;
using mozilla::UniquePtr;

already_AddRefed<nsIObjectOutputStream> NS_NewObjectOutputStream(
    nsIOutputStream* aOutputStream) {
  MOZ_ASSERT(aOutputStream);
  auto stream = mozilla::MakeRefPtr<nsBinaryOutputStream>();

  MOZ_ALWAYS_SUCCEEDS(stream->SetOutputStream(aOutputStream));
  return stream.forget();
}

already_AddRefed<nsIObjectInputStream> NS_NewObjectInputStream(
    nsIInputStream* aInputStream) {
  MOZ_ASSERT(aInputStream);
  auto stream = mozilla::MakeRefPtr<nsBinaryInputStream>();

  MOZ_ALWAYS_SUCCEEDS(stream->SetInputStream(aInputStream));
  return stream.forget();
}

NS_IMPL_ISUPPORTS(nsBinaryOutputStream, nsIObjectOutputStream,
                  nsIBinaryOutputStream, nsIOutputStream)

NS_IMETHODIMP
nsBinaryOutputStream::Flush() {
  if (NS_WARN_IF(!mOutputStream)) {
    return NS_ERROR_UNEXPECTED;
  }
  return mOutputStream->Flush();
}

NS_IMETHODIMP
nsBinaryOutputStream::Close() {
  if (NS_WARN_IF(!mOutputStream)) {
    return NS_ERROR_UNEXPECTED;
  }
  return mOutputStream->Close();
}

NS_IMETHODIMP
nsBinaryOutputStream::Write(const char* aBuf, uint32_t aCount,
                            uint32_t* aActualBytes) {
  if (NS_WARN_IF(!mOutputStream)) {
    return NS_ERROR_UNEXPECTED;
  }
  return mOutputStream->Write(aBuf, aCount, aActualBytes);
}

NS_IMETHODIMP
nsBinaryOutputStream::WriteFrom(nsIInputStream* aInStr, uint32_t aCount,
                                uint32_t* aResult) {
  MOZ_ASSERT_UNREACHABLE("WriteFrom");
  return NS_ERROR_NOT_IMPLEMENTED;
}

NS_IMETHODIMP
nsBinaryOutputStream::WriteSegments(nsReadSegmentFun aReader, void* aClosure,
                                    uint32_t aCount, uint32_t* aResult) {
  MOZ_ASSERT_UNREACHABLE("WriteSegments");
  return NS_ERROR_NOT_IMPLEMENTED;
}

NS_IMETHODIMP
nsBinaryOutputStream::IsNonBlocking(bool* aNonBlocking) {
  if (NS_WARN_IF(!mOutputStream)) {
    return NS_ERROR_UNEXPECTED;
  }
  return mOutputStream->IsNonBlocking(aNonBlocking);
}

nsresult nsBinaryOutputStream::WriteFully(const char* aBuf, uint32_t aCount) {
  if (NS_WARN_IF(!mOutputStream)) {
    return NS_ERROR_UNEXPECTED;
  }

  nsresult rv;
  uint32_t bytesWritten;

  rv = mOutputStream->Write(aBuf, aCount, &bytesWritten);
  if (NS_FAILED(rv)) {
    return rv;
  }
  if (bytesWritten != aCount) {
    return NS_ERROR_FAILURE;
  }
  return NS_OK;
}

NS_IMETHODIMP
nsBinaryOutputStream::SetOutputStream(nsIOutputStream* aOutputStream) {
  if (NS_WARN_IF(!aOutputStream)) {
    return NS_ERROR_INVALID_ARG;
  }
  mOutputStream = aOutputStream;
  mBufferAccess = do_QueryInterface(aOutputStream);
  return NS_OK;
}

NS_IMETHODIMP
nsBinaryOutputStream::WriteBoolean(bool aBoolean) { return Write8(aBoolean); }

NS_IMETHODIMP
nsBinaryOutputStream::Write8(uint8_t aByte) {
  return WriteFully((const char*)&aByte, sizeof(aByte));
}

NS_IMETHODIMP
nsBinaryOutputStream::Write16(uint16_t aNum) {
  aNum = mozilla::NativeEndian::swapToBigEndian(aNum);
  return WriteFully((const char*)&aNum, sizeof(aNum));
}

NS_IMETHODIMP
nsBinaryOutputStream::Write32(uint32_t aNum) {
  aNum = mozilla::NativeEndian::swapToBigEndian(aNum);
  return WriteFully((const char*)&aNum, sizeof(aNum));
}

NS_IMETHODIMP
nsBinaryOutputStream::Write64(uint64_t aNum) {
  nsresult rv;
  uint32_t bytesWritten;

  aNum = mozilla::NativeEndian::swapToBigEndian(aNum);
  rv = Write(reinterpret_cast<char*>(&aNum), sizeof(aNum), &bytesWritten);
  if (NS_FAILED(rv)) {
    return rv;
  }
  if (bytesWritten != sizeof(aNum)) {
    return NS_ERROR_FAILURE;
  }
  return rv;
}

NS_IMETHODIMP
nsBinaryOutputStream::WriteFloat(float aFloat) {
  static_assert(sizeof(float) == sizeof(uint32_t),
                "False assumption about sizeof(float)");
  return Write32(*reinterpret_cast<uint32_t*>(&aFloat));
}

NS_IMETHODIMP
nsBinaryOutputStream::WriteDouble(double aDouble) {
  static_assert(sizeof(double) == sizeof(uint64_t),
                "False assumption about sizeof(double)");
  return Write64(*reinterpret_cast<uint64_t*>(&aDouble));
}

NS_IMETHODIMP
nsBinaryOutputStream::WriteStringZ(const char* aString) {
  uint32_t length;
  nsresult rv;

  length = strlen(aString);
  rv = Write32(length);
  if (NS_FAILED(rv)) {
    return rv;
  }
  return WriteFully(aString, length);
}

NS_IMETHODIMP
nsBinaryOutputStream::WriteWStringZ(const char16_t* aString) {
  uint32_t length = NS_strlen(aString);
  nsresult rv = Write32(length);
  if (NS_FAILED(rv)) {
    return rv;
  }

  if (length == 0) {
    return NS_OK;
  }

#ifdef IS_BIG_ENDIAN
  rv = WriteBytes(AsBytes(Span(aString, length)));
#else
  // XXX use WriteSegments here to avoid copy!
  char16_t* copy;
  char16_t temp[64];
  if (length <= 64) {
    copy = temp;
  } else {
    copy = static_cast<char16_t*>(malloc(length * sizeof(char16_t)));
    if (!copy) {
      return NS_ERROR_OUT_OF_MEMORY;
    }
  }
  NS_ASSERTION((uintptr_t(aString) & 0x1) == 0, "aString not properly aligned");
  mozilla::NativeEndian::copyAndSwapToBigEndian(copy, aString, length);
  rv = WriteBytes(AsBytes(Span(copy, length)));
  if (copy != temp) {
    free(copy);
  }
#endif

  return rv;
}

NS_IMETHODIMP
nsBinaryOutputStream::WriteUtf8Z(const char16_t* aString) {
  return WriteStringZ(NS_ConvertUTF16toUTF8(aString).get());
}

nsresult nsBinaryOutputStream::WriteBytes(Span<const uint8_t> aBytes) {
  nsresult rv;
  uint32_t bytesWritten;

  rv = Write(reinterpret_cast<const char*>(aBytes.Elements()), aBytes.Length(),
             &bytesWritten);
  if (NS_FAILED(rv)) {
    return rv;
  }
  if (bytesWritten != aBytes.Length()) {
    return NS_ERROR_FAILURE;
  }
  return rv;
}

NS_IMETHODIMP
nsBinaryOutputStream::WriteBytesFromJS(const char* aString, uint32_t aLength) {
  return WriteBytes(AsBytes(Span(aString, aLength)));
}

NS_IMETHODIMP
nsBinaryOutputStream::WriteByteArray(const nsTArray<uint8_t>& aByteArray) {
  return WriteBytes(aByteArray);
}

NS_IMETHODIMP
nsBinaryOutputStream::WriteObject(nsISupports* aObject, bool aIsStrongRef) {
  return WriteCompoundObject(aObject, NS_GET_IID(nsISupports), aIsStrongRef);
}

NS_IMETHODIMP
nsBinaryOutputStream::WriteSingleRefObject(nsISupports* aObject) {
  return WriteCompoundObject(aObject, NS_GET_IID(nsISupports), true);
}

NS_IMETHODIMP
nsBinaryOutputStream::WriteCompoundObject(nsISupports* aObject,
                                          const nsIID& aIID,
                                          bool aIsStrongRef) {
  nsCOMPtr<nsIClassInfo> classInfo = do_QueryInterface(aObject);
  nsCOMPtr<nsISerializable> serializable = do_QueryInterface(aObject);

  // Can't deal with weak refs
  if (NS_WARN_IF(!aIsStrongRef)) {
    return NS_ERROR_UNEXPECTED;
  }
  if (NS_WARN_IF(!classInfo) || NS_WARN_IF(!serializable)) {
    return NS_ERROR_NOT_AVAILABLE;
  }

  nsCID cid;
  nsresult rv = classInfo->GetClassIDNoAlloc(&cid);
  if (NS_SUCCEEDED(rv)) {
    rv = WriteID(cid);
  } else {
    nsCID* cidptr = nullptr;
    rv = classInfo->GetClassID(&cidptr);
    if (NS_WARN_IF(NS_FAILED(rv))) {
      return rv;
    }

    rv = WriteID(*cidptr);

    free(cidptr);
  }

  if (NS_WARN_IF(NS_FAILED(rv))) {
    return rv;
  }

  rv = WriteID(aIID);
  if (NS_WARN_IF(NS_FAILED(rv))) {
    return rv;
  }

  return serializable->Write(this);
}

NS_IMETHODIMP
nsBinaryOutputStream::WriteID(const nsIID& aIID) {
  nsresult rv = Write32(aIID.m0);
  if (NS_WARN_IF(NS_FAILED(rv))) {
    return rv;
  }

  rv = Write16(aIID.m1);
  if (NS_WARN_IF(NS_FAILED(rv))) {
    return rv;
  }

  rv = Write16(aIID.m2);
  if (NS_WARN_IF(NS_FAILED(rv))) {
    return rv;
  }

  rv = WriteBytes(aIID.m3);
  if (NS_WARN_IF(NS_FAILED(rv))) {
    return rv;
  }

  return NS_OK;
}

NS_IMETHODIMP_(char*)
nsBinaryOutputStream::GetBuffer(uint32_t aLength, uint32_t aAlignMask) {
  if (mBufferAccess) {
    return mBufferAccess->GetBuffer(aLength, aAlignMask);
  }
  return nullptr;
}

NS_IMETHODIMP_(void)
nsBinaryOutputStream::PutBuffer(char* aBuffer, uint32_t aLength) {
  if (mBufferAccess) {
    mBufferAccess->PutBuffer(aBuffer, aLength);
  }
}

NS_IMPL_ISUPPORTS(nsBinaryInputStream, nsIObjectInputStream,
                  nsIBinaryInputStream, nsIInputStream)

NS_IMETHODIMP
nsBinaryInputStream::Available(uint64_t* aResult) {
  if (NS_WARN_IF(!mInputStream)) {
    return NS_ERROR_UNEXPECTED;
  }
  return mInputStream->Available(aResult);
}

NS_IMETHODIMP
nsBinaryInputStream::Read(char* aBuffer, uint32_t aCount, uint32_t* aNumRead) {
  if (NS_WARN_IF(!mInputStream)) {
    return NS_ERROR_UNEXPECTED;
  }

  // mInputStream might give us short reads, so deal with that.
  uint32_t totalRead = 0;

  uint32_t bytesRead;
  do {
    nsresult rv = mInputStream->Read(aBuffer, aCount, &bytesRead);
    if (rv == NS_BASE_STREAM_WOULD_BLOCK && totalRead != 0) {
      // We already read some data.  Return it.
      break;
    }

    if (NS_FAILED(rv)) {
      return rv;
    }

    totalRead += bytesRead;
    aBuffer += bytesRead;
    aCount -= bytesRead;
  } while (aCount != 0 && bytesRead != 0);

  *aNumRead = totalRead;

  return NS_OK;
}

// when forwarding ReadSegments to mInputStream, we need to make sure
// 'this' is being passed to the writer each time. To do this, we need
// a thunking function which keeps the real input stream around.

// the closure wrapper
struct MOZ_STACK_CLASS ReadSegmentsClosure {
  nsCOMPtr<nsIInputStream> mRealInputStream;
  void* mRealClosure;
  nsWriteSegmentFun mRealWriter;
  nsresult mRealResult;
  uint32_t mBytesRead;  // to properly implement aToOffset
};

// the thunking function
static nsresult ReadSegmentForwardingThunk(nsIInputStream* aStream,
                                           void* aClosure,
                                           const char* aFromSegment,
                                           uint32_t aToOffset, uint32_t aCount,
                                           uint32_t* aWriteCount) {
  ReadSegmentsClosure* thunkClosure =
      reinterpret_cast<ReadSegmentsClosure*>(aClosure);

  NS_ASSERTION(NS_SUCCEEDED(thunkClosure->mRealResult),
               "How did this get to be a failure status?");

  thunkClosure->mRealResult = thunkClosure->mRealWriter(
      thunkClosure->mRealInputStream, thunkClosure->mRealClosure, aFromSegment,
      thunkClosure->mBytesRead + aToOffset, aCount, aWriteCount);

  return thunkClosure->mRealResult;
}

NS_IMETHODIMP
nsBinaryInputStream::ReadSegments(nsWriteSegmentFun aWriter, void* aClosure,
                                  uint32_t aCount, uint32_t* aResult) {
  if (NS_WARN_IF(!mInputStream)) {
    return NS_ERROR_UNEXPECTED;
  }

  ReadSegmentsClosure thunkClosure = {this, aClosure, aWriter, NS_OK, 0};

  // mInputStream might give us short reads, so deal with that.
  uint32_t bytesRead;
  do {
    nsresult rv = mInputStream->ReadSegments(ReadSegmentForwardingThunk,
                                             &thunkClosure, aCount, &bytesRead);

    if (rv == NS_BASE_STREAM_WOULD_BLOCK && thunkClosure.mBytesRead != 0) {
      // We already read some data.  Return it.
      break;
    }

    if (NS_FAILED(rv)) {
      return rv;
    }

    thunkClosure.mBytesRead += bytesRead;
    aCount -= bytesRead;
  } while (aCount != 0 && bytesRead != 0 &&
           NS_SUCCEEDED(thunkClosure.mRealResult));

  *aResult = thunkClosure.mBytesRead;

  return NS_OK;
}

NS_IMETHODIMP
nsBinaryInputStream::IsNonBlocking(bool* aNonBlocking) {
  if (NS_WARN_IF(!mInputStream)) {
    return NS_ERROR_UNEXPECTED;
  }
  return mInputStream->IsNonBlocking(aNonBlocking);
}

NS_IMETHODIMP
nsBinaryInputStream::Close() {
  if (NS_WARN_IF(!mInputStream)) {
    return NS_ERROR_UNEXPECTED;
  }
  return mInputStream->Close();
}

NS_IMETHODIMP
nsBinaryInputStream::SetInputStream(nsIInputStream* aInputStream) {
  if (NS_WARN_IF(!aInputStream)) {
    return NS_ERROR_INVALID_ARG;
  }
  mInputStream = aInputStream;
  mBufferAccess = do_QueryInterface(aInputStream);
  return NS_OK;
}

NS_IMETHODIMP
nsBinaryInputStream::ReadBoolean(bool* aBoolean) {
  uint8_t byteResult;
  nsresult rv = Read8(&byteResult);
  if (NS_FAILED(rv)) {
    return rv;
  }
  *aBoolean = !!byteResult;
  return rv;
}

NS_IMETHODIMP
nsBinaryInputStream::Read8(uint8_t* aByte) {
  nsresult rv;
  uint32_t bytesRead;

  rv = Read(reinterpret_cast<char*>(aByte), sizeof(*aByte), &bytesRead);
  if (NS_FAILED(rv)) {
    return rv;
  }
  if (bytesRead != 1) {
    return NS_ERROR_FAILURE;
  }
  return rv;
}

NS_IMETHODIMP
nsBinaryInputStream::Read16(uint16_t* aNum) {
  uint32_t bytesRead;
  nsresult rv = Read(reinterpret_cast<char*>(aNum), sizeof(*aNum), &bytesRead);
  if (NS_FAILED(rv)) {
    return rv;
  }
  if (bytesRead != sizeof(*aNum)) {
    return NS_ERROR_FAILURE;
  }
  *aNum = mozilla::NativeEndian::swapFromBigEndian(*aNum);
  return rv;
}

NS_IMETHODIMP
nsBinaryInputStream::Read32(uint32_t* aNum) {
  uint32_t bytesRead;
  nsresult rv = Read(reinterpret_cast<char*>(aNum), sizeof(*aNum), &bytesRead);
  if (NS_FAILED(rv)) {
    return rv;
  }
  if (bytesRead != sizeof(*aNum)) {
    return NS_ERROR_FAILURE;
  }
  *aNum = mozilla::NativeEndian::swapFromBigEndian(*aNum);
  return rv;
}

NS_IMETHODIMP
nsBinaryInputStream::Read64(uint64_t* aNum) {
  uint32_t bytesRead;
  nsresult rv = Read(reinterpret_cast<char*>(aNum), sizeof(*aNum), &bytesRead);
  if (NS_FAILED(rv)) {
    return rv;
  }
  if (bytesRead != sizeof(*aNum)) {
    return NS_ERROR_FAILURE;
  }
  *aNum = mozilla::NativeEndian::swapFromBigEndian(*aNum);
  return rv;
}

NS_IMETHODIMP
nsBinaryInputStream::ReadFloat(float* aFloat) {
  static_assert(sizeof(float) == sizeof(uint32_t),
                "False assumption about sizeof(float)");
  return Read32(reinterpret_cast<uint32_t*>(aFloat));
}

NS_IMETHODIMP
nsBinaryInputStream::ReadDouble(double* aDouble) {
  static_assert(sizeof(double) == sizeof(uint64_t),
                "False assumption about sizeof(double)");
  return Read64(reinterpret_cast<uint64_t*>(aDouble));
}

static nsresult WriteSegmentToCString(nsIInputStream* aStream, void* aClosure,
                                      const char* aFromSegment,
                                      uint32_t aToOffset, uint32_t aCount,
                                      uint32_t* aWriteCount) {
  nsACString* outString = static_cast<nsACString*>(aClosure);

  outString->Append(aFromSegment, aCount);

  *aWriteCount = aCount;

  return NS_OK;
}

NS_IMETHODIMP
nsBinaryInputStream::ReadCString(nsACString& aString) {
  nsresult rv;
  uint32_t length, bytesRead;

  rv = Read32(&length);
  if (NS_FAILED(rv)) {
    return rv;
  }

  aString.Truncate();
  rv = ReadSegments(WriteSegmentToCString, &aString, length, &bytesRead);
  if (NS_FAILED(rv)) {
    return rv;
  }

  if (bytesRead != length) {
    return NS_ERROR_FAILURE;
  }

  return NS_OK;
}

// sometimes, WriteSegmentToString will be handed an odd-number of
// bytes, which means we only have half of the last char16_t
struct WriteStringClosure {
  char16_t* mWriteCursor;
  bool mHasCarryoverByte;
  char mCarryoverByte;
};

// there are a few cases we have to account for here:
// * even length buffer, no carryover - easy, just append
// * odd length buffer, no carryover - the last byte needs to be saved
//                                     for carryover
// * odd length buffer, with carryover - first byte needs to be used
//                              with the carryover byte, and
//                              the rest of the even length
//                              buffer is appended as normal
// * even length buffer, with carryover - the first byte needs to be
//                              used with the previous carryover byte.
//                              this gives you an odd length buffer,
//                              so you have to save the last byte for
//                              the next carryover

// same version of the above, but with correct casting and endian swapping
static nsresult WriteSegmentToString(nsIInputStream* aStream, void* aClosure,
                                     const char* aFromSegment,
                                     uint32_t aToOffset, uint32_t aCount,
                                     uint32_t* aWriteCount) {
  MOZ_ASSERT(aCount > 0, "Why are we being told to write 0 bytes?");
  static_assert(sizeof(char16_t) == 2, "We can't handle other sizes!");

  WriteStringClosure* closure = static_cast<WriteStringClosure*>(aClosure);
  char16_t* cursor = closure->mWriteCursor;

  // we're always going to consume the whole buffer no matter what
  // happens, so take care of that right now.. that allows us to
  // tweak aCount later. Do NOT move this!
  *aWriteCount = aCount;

  // if the last Write had an odd-number of bytes read, then
  if (closure->mHasCarryoverByte) {
    // re-create the two-byte sequence we want to work with
    char bytes[2] = {closure->mCarryoverByte, *aFromSegment};
    *cursor = *(char16_t*)bytes;
    // Now the little endianness dance
    mozilla::NativeEndian::swapToBigEndianInPlace(cursor, 1);
    ++cursor;

    // now skip past the first byte of the buffer.. code from here
    // can assume normal operations, but should not assume aCount
    // is relative to the ORIGINAL buffer
    ++aFromSegment;
    --aCount;

    closure->mHasCarryoverByte = false;
  }

  // this array is possibly unaligned... be careful how we access it!
  const char16_t* unicodeSegment =
      reinterpret_cast<const char16_t*>(aFromSegment);

  // calculate number of full characters in segment (aCount could be odd!)
  uint32_t segmentLength = aCount / sizeof(char16_t);

  // copy all data into our aligned buffer.  byte swap if necessary.
  // cursor may be unaligned, so we cannot use copyAndSwapToBigEndian directly
  memcpy(cursor, unicodeSegment, segmentLength * sizeof(char16_t));
  char16_t* end = cursor + segmentLength;
  mozilla::NativeEndian::swapToBigEndianInPlace(cursor, segmentLength);
  closure->mWriteCursor = end;

  // remember this is the modifed aCount and aFromSegment,
  // so that will take into account the fact that we might have
  // skipped the first byte in the buffer
  if (aCount % sizeof(char16_t) != 0) {
    // we must have had a carryover byte, that we'll need the next
    // time around
    closure->mCarryoverByte = aFromSegment[aCount - 1];
    closure->mHasCarryoverByte = true;
  }

  return NS_OK;
}

NS_IMETHODIMP
nsBinaryInputStream::ReadString(nsAString& aString) {
  nsresult rv;
  uint32_t length, bytesRead;

  rv = Read32(&length);
  if (NS_FAILED(rv)) {
    return rv;
  }

  if (length == 0) {
    aString.Truncate();
    return NS_OK;
  }

  // pre-allocate output buffer, and get direct access to buffer...
  if (!aString.SetLength(length, mozilla::fallible)) {
    return NS_ERROR_OUT_OF_MEMORY;
  }

  WriteStringClosure closure;
  closure.mWriteCursor = aString.BeginWriting();
  closure.mHasCarryoverByte = false;

  rv = ReadSegments(WriteSegmentToString, &closure, length * sizeof(char16_t),
                    &bytesRead);
  if (NS_FAILED(rv)) {
    return rv;
  }

  NS_ASSERTION(!closure.mHasCarryoverByte, "some strange stream corruption!");

  if (bytesRead != length * sizeof(char16_t)) {
    return NS_ERROR_FAILURE;
  }

  return NS_OK;
}

nsresult nsBinaryInputStream::ReadBytesToBuffer(uint32_t aLength,
                                                uint8_t* aBuffer) {
  uint32_t bytesRead;
  nsresult rv = Read(reinterpret_cast<char*>(aBuffer), aLength, &bytesRead);
  if (NS_FAILED(rv)) {
    return rv;
  }
  if (bytesRead != aLength) {
    return NS_ERROR_FAILURE;
  }

  return NS_OK;
}

NS_IMETHODIMP
nsBinaryInputStream::ReadBytes(uint32_t aLength, char** aResult) {
  char* s = static_cast<char*>(malloc(aLength));
  if (!s) {
    return NS_ERROR_OUT_OF_MEMORY;
  }

  nsresult rv = ReadBytesToBuffer(aLength, reinterpret_cast<uint8_t*>(s));
  if (NS_FAILED(rv)) {
    free(s);
    return rv;
  }

  *aResult = s;
  return NS_OK;
}

NS_IMETHODIMP
nsBinaryInputStream::ReadByteArray(uint32_t aLength,
                                   nsTArray<uint8_t>& aResult) {
  if (!aResult.SetLength(aLength, mozilla::fallible)) {
    return NS_ERROR_OUT_OF_MEMORY;
  }
  nsresult rv = ReadBytesToBuffer(aLength, aResult.Elements());
  if (NS_FAILED(rv)) {
    aResult.Clear();
  }
  return rv;
}

NS_IMETHODIMP
nsBinaryInputStream::ReadArrayBuffer(uint64_t aLength,
                                     JS::Handle<JS::Value> aBuffer,
                                     JSContext* aCx, uint64_t* aReadLength) {
  if (!aBuffer.isObject()) {
    return NS_ERROR_FAILURE;
  }
  JS::Rooted<JSObject*> buffer(aCx, &aBuffer.toObject());
  if (!JS::IsArrayBufferObject(buffer)) {
    return NS_ERROR_FAILURE;
  }

  size_t bufferLength = JS::GetArrayBufferByteLength(buffer);
  if (bufferLength < aLength) {
    return NS_ERROR_FAILURE;
  }

  uint32_t bufSize = std::min<uint64_t>(aLength, 4096);
  UniquePtr<char[]> buf = MakeUnique<char[]>(bufSize);

  uint64_t pos = 0;
  *aReadLength = 0;
  do {
    // Read data into temporary buffer.
    uint32_t bytesRead;
    uint32_t amount = std::min<uint64_t>(aLength - pos, bufSize);
    nsresult rv = Read(buf.get(), amount, &bytesRead);
    if (NS_WARN_IF(NS_FAILED(rv))) {
      return rv;
    }
    MOZ_ASSERT(bytesRead <= amount);

    if (bytesRead == 0) {
      break;
    }

    // Copy data into actual buffer.

    JS::AutoCheckCannotGC nogc;
    bool isShared;
    if (bufferLength != JS::GetArrayBufferByteLength(buffer)) {
      return NS_ERROR_FAILURE;
    }

    char* data = reinterpret_cast<char*>(
        JS::GetArrayBufferData(buffer, &isShared, nogc));
    MOZ_ASSERT(!isShared);  // Implied by JS::GetArrayBufferData()
    if (!data) {
      return NS_ERROR_FAILURE;
    }

    *aReadLength += bytesRead;
    PodCopy(data + pos, buf.get(), bytesRead);

    pos += bytesRead;
  } while (pos < aLength);

  return NS_OK;
}

NS_IMETHODIMP
nsBinaryInputStream::ReadObject(bool aIsStrongRef, nsISupports** aObject) {
  nsCID cid;
  nsIID iid;
  nsresult rv = ReadID(&cid);
  if (NS_WARN_IF(NS_FAILED(rv))) {
    return rv;
  }

  rv = ReadID(&iid);
  if (NS_WARN_IF(NS_FAILED(rv))) {
    return rv;
  }

  // HACK: Intercept old (pre-gecko6) nsIURI IID, and replace with
  // the updated IID, so that we're QI'ing to an actual interface.
  // (As soon as we drop support for upgrading from pre-gecko6, we can
  // remove this chunk.)
  static const nsIID oldURIiid = {
      0x7a22cc0,
      0xce5,
      0x11d3,
      {0x93, 0x31, 0x0, 0x10, 0x4b, 0xa0, 0xfd, 0x40}};

  // hackaround for bug 670542
  static const nsIID oldURIiid2 = {
      0xd6d04c36,
      0x0fa4,
      0x4db3,
      {0xbe, 0x05, 0x4a, 0x18, 0x39, 0x71, 0x03, 0xe2}};

  // hackaround for bug 682031
  static const nsIID oldURIiid3 = {
      0x12120b20,
      0x0929,
      0x40e9,
      {0x88, 0xcf, 0x6e, 0x08, 0x76, 0x6e, 0x8b, 0x23}};

  // hackaround for bug 1195415
  static const nsIID oldURIiid4 = {
      0x395fe045,
      0x7d18,
      0x4adb,
      {0xa3, 0xfd, 0xaf, 0x98, 0xc8, 0xa1, 0xaf, 0x11}};

  if (iid.Equals(oldURIiid) || iid.Equals(oldURIiid2) ||
      iid.Equals(oldURIiid3) || iid.Equals(oldURIiid4)) {
    const nsIID newURIiid = NS_IURI_IID;
    iid = newURIiid;
  }

  // Hack around bug 1508939
  // The old CSP serialization can't be handled cleanly when
  // it's embedded in an old style principal
  static const nsIID oldCSPiid = {
      0xb3c4c0ae,
      0xbd5e,
      0x4cad,
      {0x87, 0xe0, 0x8d, 0x21, 0x0d, 0xbb, 0x3f, 0x9f}};
  if (iid.Equals(oldCSPiid)) {
    return NS_ERROR_FAILURE;
  }
  // END HACK

  // HACK:  Service workers store resource security info on disk in the dom
  //        Cache API.  When the uuid of the nsIX509Cert interface changes
  //        these serialized objects cannot be loaded any more.  This hack
  //        works around this issue.

  // hackaround for bug 1247580 (FF45 to FF46 transition)
  static const nsIID oldCertIID = {
      0xf8ed8364,
      0xced9,
      0x4c6e,
      {0x86, 0xba, 0x48, 0xaf, 0x53, 0xc3, 0x93, 0xe6}};

  if (iid.Equals(oldCertIID)) {
    const nsIID newCertIID = NS_IX509CERT_IID;
    iid = newCertIID;
  }
  // END HACK

  nsCOMPtr<nsISupports> object = do_CreateInstance(cid, &rv);
  if (NS_WARN_IF(NS_FAILED(rv))) {
    return rv;
  }

  nsCOMPtr<nsISerializable> serializable = do_QueryInterface(object);
  if (NS_WARN_IF(!serializable)) {
    return NS_ERROR_UNEXPECTED;
  }

  rv = serializable->Read(this);
  if (NS_WARN_IF(NS_FAILED(rv))) {
    return rv;
  }

  return object->QueryInterface(iid, reinterpret_cast<void**>(aObject));
}

NS_IMETHODIMP
nsBinaryInputStream::ReadID(nsID* aResult) {
  nsresult rv = Read32(&aResult->m0);
  if (NS_WARN_IF(NS_FAILED(rv))) {
    return rv;
  }

  rv = Read16(&aResult->m1);
  if (NS_WARN_IF(NS_FAILED(rv))) {
    return rv;
  }

  rv = Read16(&aResult->m2);
  if (NS_WARN_IF(NS_FAILED(rv))) {
    return rv;
  }

  const uint32_t toRead = sizeof(aResult->m3);
  uint32_t bytesRead = 0;
  rv = Read(reinterpret_cast<char*>(&aResult->m3[0]), toRead, &bytesRead);
  if (NS_WARN_IF(NS_FAILED(rv))) {
    return rv;
  }
  if (bytesRead != toRead) {
    return NS_ERROR_FAILURE;
  }

  return NS_OK;
}

NS_IMETHODIMP_(char*)
nsBinaryInputStream::GetBuffer(uint32_t aLength, uint32_t aAlignMask) {
  if (mBufferAccess) {
    return mBufferAccess->GetBuffer(aLength, aAlignMask);
  }
  return nullptr;
}

NS_IMETHODIMP_(void)
nsBinaryInputStream::PutBuffer(char* aBuffer, uint32_t aLength) {
  if (mBufferAccess) {
    mBufferAccess->PutBuffer(aBuffer, aLength);
  }
}