magic_header.hpp

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// SPDX-FileCopyrightText: 2006-2025 Knut Reinert & Freie Universität Berlin
// SPDX-FileCopyrightText: 2016-2025 Knut Reinert & MPI für molekulare Genetik
// SPDX-License-Identifier: BSD-3-Clause

 
#pragma once
 
#include <array>
#include <bit>
#include <span>
#include <string>
#include <type_traits>
#include <vector>
 
#include <seqan3/core/detail/template_inspection.hpp>
#include <seqan3/utility/concept.hpp>
#include <seqan3/utility/type_pack/traits.hpp>
 
namespace seqan3::detail
{

struct gz_compression
{
    static inline std::vector<std::string> file_extensions{{"gz"}};

    static constexpr std::array<char, 3> magic_header{'\x1f', '\x8b', '\x08'};
};

struct bz2_compression
{
    static inline std::vector<std::string> file_extensions{{"bz2"}};

    static constexpr std::array<char, 3> magic_header{'\x42', '\x5a', '\x68'};
};

struct zstd_compression
{
    static inline std::vector<std::string> file_extensions{{"zst"}};

    static constexpr std::array<char, 4> magic_header{'\x28', '\xb5', '\x2f', '\xfd'};
};

struct bgzf_compression
{
    static inline std::vector<std::string> file_extensions{{"bgzf"}};

    static constexpr std::array<char, 18> magic_header{
        //  ID1                              ID2                              CM
        gz_compression::magic_header[0],
        gz_compression::magic_header[1],
        gz_compression::magic_header[2],
        //  FLG     [MTIME                       ]  XFL     OS      [XLEN        ]
        '\x04',
        '\x00',
        '\x00',
        '\x00',
        '\x00',
        '\x00',
        '\xff',
        '\x06',
        '\x00',
        //  B       C       [SLEN        ]  [BSIZE       ]
        '\x42',
        '\x43',
        '\x02',
        '\x00',
        '\x00',
        '\x00'};

    template <typename char_t, size_t extend>
    static bool validate_header(std::span<char_t, extend> header)
    {
        static_assert(std::equality_comparable_with<char_t, char>,
                      "The given char type of the span must be comparable with char.");
 
        static constexpr auto id1_pos = std::endian::native == std::endian::little ? 10 : 11;
 
        return (header[0] == magic_header[0] &&           // GZ_ID1
                header[1] == magic_header[1] &&           // GZ_ID2
                header[2] == magic_header[2] &&           // GZ_CM
                (header[3] & magic_header[3]) != 0 &&     // FLG_FEXTRA
                header[id1_pos] == magic_header[10] &&    // BGZF_ID1
                header[12] == magic_header[12] &&         // BGZF_ID2
                header[13] == magic_header[13] &&         // BGZF_SLEN
                header[id1_pos + 4] == magic_header[14]); // BGZF_XLEN
    }
};

using compression_formats = pack_traits::drop_front<void
#if SEQAN3_HAS_ZLIB
                                                    ,
                                                    gz_compression,
                                                    bgzf_compression
#endif // SEQAN3_HAS_ZLIB
#if SEQAN3_HAS_BZIP2
                                                    ,
                                                    bz2_compression
#endif // SEQAN3_HAS_BZIP2
#if SEQAN3_HAS_ZSTD
                                                    ,
                                                    zstd_compression
#endif // SEQAN3_HAS_ZSTD
                                                    >;
 
} // namespace seqan3::detail