data_stream.h

/* ScummVM - Graphic Adventure Engine
 *
 * ScummVM is the legal property of its developers, whose names
 * are too numerous to list here. Please refer to the COPYRIGHT
 * file distributed with this source distribution.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

//=============================================================================
//
// Standard AGS stream implementation for reading raw data with support for
// converting to opposite endianess. Most I/O devices should inherit this
// class and provide implementation for basic reading and writing only.
//
//=============================================================================

#ifndef AGS_SHARED_UTIL_DATASTREAM_H
#define AGS_SHARED_UTIL_DATASTREAM_H

#include "ags/shared/util/bbop.h"
#include "ags/shared/util/stream.h"

namespace AGS3 {
namespace AGS {
namespace Shared {

class DataStream : public Stream {
public:
    DataStream(DataEndianess stream_endianess = kLittleEndian);
    ~DataStream() override;

    int16_t ReadInt16() override;
    int32_t ReadInt32() override;
    int64_t ReadInt64() override;

    //
    // Read- and WriteArray methods return number of full elements (NOT bytes)
    // read or written, or -1 if end of stream is reached
    //
    // Note that ReadArray and WriteArray do NOT convert byte order even when
    // work with data of different endianess; they are meant for optimal
    // reading and writing blocks of raw bytes
    inline size_t ReadArray(void *buffer, size_t elem_size, size_t count) override {
        return Read(buffer, elem_size * count) / elem_size;
    }

    inline size_t ReadArrayOfInt16(int16_t *buffer, size_t count) override {
        return MustSwapBytes() ?
               ReadAndConvertArrayOfInt16(buffer, count) : ReadArray(buffer, sizeof(int16_t), count);
    }

    inline size_t ReadArrayOfInt32(int32_t *buffer, size_t count) override {
        return MustSwapBytes() ?
               ReadAndConvertArrayOfInt32(buffer, count) : ReadArray(buffer, sizeof(int32_t), count);
    }

    inline size_t ReadArrayOfInt64(int64_t *buffer, size_t count) override {
        return MustSwapBytes() ?
               ReadAndConvertArrayOfInt64(buffer, count) : ReadArray(buffer, sizeof(int64_t), count);
    }

    size_t  WriteInt16(int16_t val) override;
    size_t  WriteInt32(int32_t val) override;
    size_t  WriteInt64(int64_t val) override;

    inline size_t WriteArray(const void *buffer, size_t elem_size, size_t count) override {
        return Write(buffer, elem_size * count) / elem_size;
    }

    inline size_t WriteArrayOfInt16(const int16_t *buffer, size_t count) override {
        return MustSwapBytes() ?
               WriteAndConvertArrayOfInt16(buffer, count) : WriteArray(buffer, sizeof(int16_t), count);
    }

    inline size_t WriteArrayOfInt32(const int32_t *buffer, size_t count) override {
        return MustSwapBytes() ?
               WriteAndConvertArrayOfInt32(buffer, count) : WriteArray(buffer, sizeof(int32_t), count);
    }

    inline size_t WriteArrayOfInt64(const int64_t *buffer, size_t count) override {
        return MustSwapBytes() ?
               WriteAndConvertArrayOfInt64(buffer, count) : WriteArray(buffer, sizeof(int64_t), count);
    }

    protected:
    DataEndianess _streamEndianess;

    // Helper methods for reading/writing arrays of basic types and
    // converting their elements to opposite endianess (swapping bytes).
    size_t  ReadAndConvertArrayOfInt16(int16_t *buffer, size_t count);
    size_t  ReadAndConvertArrayOfInt32(int32_t *buffer, size_t count);
    size_t  ReadAndConvertArrayOfInt64(int64_t *buffer, size_t count);
    size_t  WriteAndConvertArrayOfInt16(const int16_t *buffer, size_t count);
    size_t  WriteAndConvertArrayOfInt32(const int32_t *buffer, size_t count);
    size_t  WriteAndConvertArrayOfInt64(const int64_t *buffer, size_t count);

    inline bool MustSwapBytes() {
        return kDefaultSystemEndianess != _streamEndianess;
    }

    inline void ConvertInt16(int16_t &val) {
        if (MustSwapBytes()) val = BBOp::SwapBytesInt16(val);
    }
    inline void ConvertInt32(int32_t &val) {
        if (MustSwapBytes()) val = BBOp::SwapBytesInt32(val);
    }
    inline void ConvertInt64(int64_t &val) {
        if (MustSwapBytes()) val = BBOp::SwapBytesInt64(val);
    }
};

//
// DataStreamSection wraps another stream and restricts its access
// to a particular range of offsets of the base stream.
// StreamSection does NOT own the base stream, and closing
// a "stream section" does NOT close the base stream.
// Base stream must stay in memory for as long as there are
// "stream sections" referring it.
class DataStreamSection : public DataStream {
public:
    // Constructs a StreamSection over a base stream,
    // restricting working range to [start, end), i.e. end offset is
    // +1 past allowed position.
    DataStreamSection(Stream *base, soff_t start, soff_t end);
    const char *GetPath() const { return _base->GetPath().GetCStr(); }
    bool EOS() const override { return _position >= _end; }
    bool GetError() const override { return _base->GetError(); }
    soff_t GetLength() const override { return _end - _start; }
    soff_t GetPosition() const override { return _position - _start; }
    size_t Read(void *buffer, size_t len) override;
    int32_t ReadByte() override;
    size_t Write(const void *buffer, size_t len) override;
    int32_t WriteByte(uint8_t b) override;
    soff_t Seek(soff_t offset, StreamSeek origin = kSeekCurrent) override;
    bool Flush() override { return _base->Flush(); }
    void Close() override;

private:
    Stream *_base = nullptr;
    soff_t _start = 0;
    soff_t _end = 0;
    soff_t _position = 0;
};

} // namespace Shared
} // namespace AGS
} // namespace AGS3

#endif