gzip.hpp

图论必用

        // reset the decoder
        //impl_type::reset(false, true);
        base_type::close(src, BOOST_IOS::in);

        flags_ = 0;

        // now seek
        std::streamsize nuint32s = off/sizeof(uint32_t);
        std::streamsize nuint8s = off%sizeof(uint32_t);

        uint32_t four_bytes;
        uint8_t one_byte;

        while (nuint32s > 0)
        {
            read(src, (char_type*)(&four_bytes), sizeof(uint32_t));
            --nuint32s;
            rval += sizeof(uint32_t);
        }

        while (nuint8s > 0)
        {
            read(src, (char_type*)(&one_byte), sizeof(uint8_t));
            --nuint8s;
            rval += sizeof(uint8_t);
        }

        return (rval);        

    }

    template<typename Source>
    std::streamsize read(Source& src, char_type* s, std::streamsize n)
    {
        if ((flags_ & f_header_read) == 0) {
            non_blocking_adapter<Source> nb(src);
            read_header(nb);
            flags_ |= f_header_read;
        }

        if ((flags_ & f_footer_read) != 0)
            return -1;
        
        try {
            std::streamsize result = 0;
            std::streamsize amt;
            if ((amt = base_type::read(src, s, n)) != -1) {
                result += amt;
                if (amt < n) { // Double check for EOF.
                    amt = base_type::read(src, s + result, n - result);
                    if (amt != -1)
                        result += amt;
                }
            }
            if (amt == -1) {
                non_blocking_adapter<Source> nb(src);
                read_footer(nb);
                flags_ |= f_footer_read;
            }
            return result;
        } catch (const zlib_error& e) {
            throw gzip_error(e);
        }
    }

    template<typename Source>
    void close(Source& src)
    {
        try {
            base_type::close(src, BOOST_IOS::in);
            flags_ = 0;
        } catch (const zlib_error& e) {
            throw gzip_error(e);
        }
    }

    std::string file_name() const { return file_name_; }
    std::string comment() const { return comment_; }
    bool text() const { return (flags_ & gzip::flags::text) != 0; }
    int os() const { return os_; }
    std::time_t mtime() const { return mtime_; }
private:
    typedef basic_zlib_decompressor<Alloc>     base_type;
    typedef BOOST_IOSTREAMS_CHAR_TRAITS(char)  traits_type;
    static bool is_eof(int c) { return traits_type::eq_int_type(c, EOF); }
    static gzip_params make_params(int window_bits);

    template<typename Source>
    static uint8_t read_uint8(Source& src, int error)
     {
        int c;
        if ((c = boost::iostreams::get(src)) == EOF || c == WOULD_BLOCK)
            throw gzip_error(error);
        return static_cast<uint8_t>(traits_type::to_char_type(c));
    }

    template<typename Source>
    static uint32_t read_uint32(Source& src, int error)
    {
        uint8_t b1 = read_uint8(src, error);
        uint8_t b2 = read_uint8(src, error);
        uint8_t b3 = read_uint8(src, error);
        uint8_t b4 = read_uint8(src, error);
        return b1 + (b2 << 8) + (b3 << 16) + (b4 << 24);
    }

    template<typename Source>
    std::string read_string(Source& src)
    {
        std::string result;
        while (true) {
            int c;
            if (is_eof(c = boost::iostreams::get(src)))
                throw gzip_error(gzip::bad_header);
            else if (c == 0)
                return result;
            else
                result += static_cast<char>(c);
        }
    }

    template<typename Source>
    void read_header(Source& src) // Source is non-blocking.
    {
        // Reset saved values.
        #if BOOST_WORKAROUND(__GNUC__, == 2) && defined(__STL_CONFIG_H) || \
            BOOST_WORKAROUND(BOOST_DINKUMWARE_STDLIB, == 1) \
            /**/
            file_name_.erase(0, std::string::npos);
            comment_.erase(0, std::string::npos);
        #else
            file_name_.clear();
            comment_.clear();
        #endif
        os_ = gzip::os_unknown;
        mtime_ = 0;

        int flags;

        // Read header, without checking header crc.
        if ( boost::iostreams::get(src) != gzip::magic::id1 ||   // ID1.
             boost::iostreams::get(src) != gzip::magic::id2 ||   // ID2.
             is_eof(boost::iostreams::get(src)) ||               // CM.
             is_eof(flags = boost::iostreams::get(src)) )        // FLG.
        {
            throw gzip_error(gzip::bad_header);
        }
        mtime_ = read_uint32(src, gzip::bad_header);        // MTIME.
        read_uint8(src, gzip::bad_header);                 // XFL.
        os_ = read_uint8(src, gzip::bad_header);          // OS.
        if (flags & boost::iostreams::gzip::flags::text)
            flags_ |= f_text;

        // Skip extra field. (From J. Halleaux; see note at top.)
        if (flags & gzip::flags::extra) {
            int length = 
                static_cast<int>(
                    read_uint8(src, gzip::bad_header) +
                    (read_uint8(src, gzip::bad_header) << 8)
                );
            // length is garbage if EOF but the loop below will quit anyway.
            do { }
            while (length-- != 0 && !is_eof(boost::iostreams::get(src)));
        }

        if (flags & gzip::flags::name)          // Read file name.
            file_name_ = read_string(src);
        if (flags & gzip::flags::comment)       // Read comment.
            comment_ = read_string(src);
        if (flags & gzip::flags::header_crc) {  // Skip header crc.
            read_uint8(src, gzip::bad_header);
            read_uint8(src, gzip::bad_header);
        }
    }

    template<typename Source>
    void read_footer(Source& src)
    {
        typename base_type::string_type footer = 
            this->unconsumed_input();
        int c;
        while (!is_eof(c = boost::iostreams::get(src)))
            footer += c;
        detail::range_adapter<input, std::string> 
            rng(footer.begin(), footer.end());
        if (read_uint32(rng, gzip::bad_footer) != this->crc())
            throw gzip_error(gzip::bad_crc);
        if (static_cast<int>(read_uint32(rng, gzip::bad_footer)) != this->total_out())
            throw gzip_error(gzip::bad_length);
    }
    enum flag_type {
        f_header_read  = 1,
        f_footer_read  = f_header_read << 1,
        f_text         = f_footer_read << 1
    };
    std::string  file_name_;
    std::string  comment_;
    int          os_;
    std::time_t  mtime_;
    int          flags_;
};
BOOST_IOSTREAMS_PIPABLE(basic_gzip_decompressor, 1)

typedef basic_gzip_decompressor<> gzip_decompressor;

//------------------Implementation of gzip_compressor-------------------------//

template<typename Alloc>
basic_gzip_compressor<Alloc>::basic_gzip_compressor
    (const gzip_params& p, int buffer_size)
    : base_type(normalize_params(p), buffer_size),
      offset_(0), flags_(0)
{
    // Calculate gzip header.
    bool has_name = !p.file_name.empty();
    bool has_comment = !p.comment.empty();

    std::string::size_type length =
        10 +
        (has_name ? p.file_name.size() + 1 : 0) +
        (has_comment ? p.comment.size() + 1 : 0);
        // + 2; // Header crc confuses gunzip.
    int flags =
        //gzip::flags::header_crc +
        (has_name ? gzip::flags::name : 0) +
        (has_comment ? gzip::flags::comment : 0);
    int extra_flags =
        ( p.level == zlib::best_compression ?
              gzip::extra_flags::best_compression :
              0 ) +
        ( p.level == zlib::best_speed ?
              gzip::extra_flags::best_speed :
              0 );
    header_.reserve(length);
    header_ += gzip::magic::id1;                         // ID1.
    header_ += gzip::magic::id2;                         // ID2.
    header_ += gzip::method::deflate;                    // CM.
    header_ += static_cast<char>(flags);                 // FLG.
    header_ += static_cast<char>(0xFF & p.mtime);        // MTIME.
    header_ += static_cast<char>(0xFF & (p.mtime >> 8));
    header_ += static_cast<char>(0xFF & (p.mtime >> 16));
    header_ += static_cast<char>(0xFF & (p.mtime >> 24));
    header_ += static_cast<char>(extra_flags);           // XFL.
    header_ += static_cast<char>(gzip::os_unknown);      // OS.
    if (has_name) {
        header_ += p.file_name;
        header_ += '\0';
    }
    if (has_comment) {
        header_ += p.comment;
        header_ += '\0';
    }
}

template<typename Alloc>
gzip_params basic_gzip_compressor<Alloc>::normalize_params(gzip_params p)
{
    p.noheader = true;
    p.calculate_crc = true;
    return p;
}

template<typename Alloc>
void basic_gzip_compressor<Alloc>::prepare_footer()
{
    boost::iostreams::back_insert_device<std::string> out(footer_);
    write_long(this->crc(), out);
    write_long(this->total_in(), out);
    flags_ |= f_body_done;
    offset_ = 0;
}

template<typename Alloc>
std::streamsize basic_gzip_compressor<Alloc>::read_string
    (char* s, std::streamsize n, std::string& str)
{
    using namespace std;
    streamsize avail =
        static_cast<streamsize>(str.size() - offset_);
    streamsize amt = (std::min)(avail, n);
    std::copy( str.data() + offset_,
               str.data() + offset_ + amt,
               s );
    offset_ += amt;
    if ( !(flags_ & f_header_done) &&
         offset_ == static_cast<std::size_t>(str.size()) )
    {
        flags_ |= f_header_done;
    }
    return amt;
}

//------------------Implementation of gzip_decompressor-----------------------//

template<typename Alloc>
basic_gzip_decompressor<Alloc>::basic_gzip_decompressor
    (int window_bits, int buffer_size)
    : base_type(make_params(window_bits), buffer_size),
      os_(gzip::os_unknown), mtime_(0), flags_(0)
    { }

template<typename Alloc>
gzip_params basic_gzip_decompressor<Alloc>::make_params(int window_bits)
{
    gzip_params p;
    p.window_bits = window_bits;
    p.noheader = true;
    p.calculate_crc = true;
    return p;
}

//----------------------------------------------------------------------------//

} } // End namespaces iostreams, boost.

#if defined(BOOST_MSVC)
# pragma warning(pop)
#endif

#endif // #ifndef BOOST_IOSTREAMS_GZIP_HPP_INCLUDED