GZFileAdapter.cc

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#include "GZFileAdapter.hh"
#include "ZlibInflate.hh"
#include "FileException.hh"
 
namespace openmsx {
 
constexpr uint8_t ASCII_FLAG  = 0x01; // bit 0 set: file probably ascii text
constexpr uint8_t HEAD_CRC    = 0x02; // bit 1 set: header CRC present
constexpr uint8_t EXTRA_FIELD = 0x04; // bit 2 set: extra field present
constexpr uint8_t ORIG_NAME   = 0x08; // bit 3 set: original file name present
constexpr uint8_t COMMENT     = 0x10; // bit 4 set: file comment present
constexpr uint8_t RESERVED    = 0xE0; // bits 5..7: reserved
 
 
GZFileAdapter::GZFileAdapter(std::unique_ptr<FileBase> file_)
        : CompressedFileAdapter(std::move(file_))
{
}
 
[[nodiscard]] static bool skipHeader(ZlibInflate& zlib, std::string& originalName)
{
        // check magic bytes
        if (zlib.get16LE() != 0x8B1F) {
                return false;
        }
 
        uint8_t method = zlib.getByte();
        uint8_t flags = zlib.getByte();
        if (method != Z_DEFLATED || (flags & RESERVED) != 0) {
                return false;
        }
 
        // Discard time, xflags and OS code:
        zlib.skip(6);
 
        if ((flags & EXTRA_FIELD) != 0) {
                // skip the extra field
                int len  = zlib.get16LE();
                zlib.skip(len);
        }
        if ((flags & ORIG_NAME) != 0) {
                // get the original file name
                originalName = zlib.getCString();
        }
        if ((flags & COMMENT) != 0) {
                // skip the .gz file comment
                (void)zlib.getCString();
        }
        if ((flags & HEAD_CRC) != 0) {
                // skip the header crc
                zlib.skip(2);
        }
        return true;
}
 
void GZFileAdapter::decompress(FileBase& f, Decompressed& d)
{
        ZlibInflate zlib(f.mmap());
        if (!skipHeader(zlib, d.originalName)) {
                throw FileException("Not a gzip header");
        }
        d.size = zlib.inflate(d.buf);
}
 
} // namespace openmsx