IOBuffers.h

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2; -*- */
/* 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 IOBuffers_h
#define IOBuffers_h

#include "mozilla/Assertions.h"
#include "mozilla/CheckedInt.h"
#include "mozilla/EndianUtils.h"
#include "mozilla/EnumSet.h"
#include "mozilla/Range.h"
#include "mozilla/Span.h"
#include "nsString.h"
#include "nsTArray.h"

namespace mozilla {
namespace loader {

class OutputBuffer {
 public:
  OutputBuffer() {}

  uint8_t* write(size_t size) {
    auto buf = data.AppendElements(size);
    cursor_ += size;
    return buf;
  }

  void codeUint8(const uint8_t& val) { *write(sizeof val) = val; }

  template <typename T>
  void codeUint8(const EnumSet<T>& val) {
    // EnumSets are always represented as uint32_t values, so we need to
    // assert that the value actually fits in a uint8 before writing it.
    uint32_t value = val.serialize();
    codeUint8(CheckedUint8(value).value());
  }

  void codeUint16(const uint16_t& val) {
    LittleEndian::writeUint16(write(sizeof val), val);
  }

  void codeUint32(const uint32_t& val) {
    LittleEndian::writeUint32(write(sizeof val), val);
  }

  void codeString(const nsCString& str) {
    auto len = CheckedUint16(str.Length()).value();

    codeUint16(len);
    memcpy(write(len), str.BeginReading(), len);
  }

  size_t cursor() const { return cursor_; }

  uint8_t* Get() { return data.Elements(); }

  const uint8_t* Get() const { return data.Elements(); }

 private:
  nsTArray<uint8_t> data;
  size_t cursor_ = 0;
};

class InputBuffer {
 public:
  explicit InputBuffer(const Range<uint8_t>& buffer) : data(buffer) {}

  const uint8_t* read(size_t size) {
    MOZ_ASSERT(checkCapacity(size));

    auto buf = &data[cursor_];
    cursor_ += size;
    return buf;
  }

  bool codeUint8(uint8_t& val) {
    if (checkCapacity(sizeof val)) {
      val = *read(sizeof val);
    }
    return !error_;
  }

  template <typename T>
  bool codeUint8(EnumSet<T>& val) {
    uint8_t value;
    if (codeUint8(value)) {
      val.deserialize(value);
    }
    return !error_;
  }

  bool codeUint16(uint16_t& val) {
    if (checkCapacity(sizeof val)) {
      val = LittleEndian::readUint16(read(sizeof val));
    }
    return !error_;
  }

  bool codeUint32(uint32_t& val) {
    if (checkCapacity(sizeof val)) {
      val = LittleEndian::readUint32(read(sizeof val));
    }
    return !error_;
  }

  bool codeString(nsCString& str) {
    uint16_t len;
    if (codeUint16(len)) {
      if (checkCapacity(len)) {
        str.SetLength(len);
        memcpy(str.BeginWriting(), read(len), len);
      }
    }
    return !error_;
  }

  bool error() { return error_; }

  bool finished() { return error_ || !remainingCapacity(); }

  size_t remainingCapacity() { return data.length() - cursor_; }

  size_t cursor() const { return cursor_; }

  const uint8_t* Get() const { return data.begin().get(); }

 private:
  bool checkCapacity(size_t size) {
    if (size > remainingCapacity()) {
      error_ = true;
    }
    return !error_;
  }

  bool error_ = false;

 public:
  const Range<uint8_t>& data;
  size_t cursor_ = 0;
};

}  // namespace loader
}  // namespace mozilla

#endif  // IOBuffers_h