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LibCompress: Use newly created Zlib header structure when decompressing

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This way we can get rid of some magic numbers.
This commit is contained in:
Karol Kosek 2022-06-17 09:26:04 +02:00 • committed by Linus Groh
parent 20575ea1f3
commit 42abe1df77
2 changed files with 16 additions and 25 deletions
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33
Userland/Libraries/LibCompress/Zlib.cpp
View file

@ -11,37 +11,32 @@
namespace Compress { namespace Compress {
constexpr static size_t Adler32Size = sizeof(u32);
Optional<Zlib> Zlib::try_create(ReadonlyBytes data) Optional<Zlib> Zlib::try_create(ReadonlyBytes data)
{ {
if (data.size() < 6) if (data.size() < (sizeof(ZlibHeader) + Adler32Size))
return {}; // header + footer size is 6 return {};
Zlib zlib { data }; ZlibHeader header { .as_u16 = data.at(0) << 8 | data.at(1) };
u8 compression_info = data.at(0); if (header.compression_method != ZlibCompressionMethod::Deflate || header.compression_info > 7)
u8 flags = data.at(1);
zlib.m_compression_method = compression_info & 0xF;
zlib.m_compression_info = (compression_info >> 4) & 0xF;
zlib.m_check_bits = flags & 0xF;
zlib.m_has_dictionary = (flags >> 5) & 0x1;
zlib.m_compression_level = (flags >> 6) & 0x3;
if (zlib.m_compression_method != 8 || zlib.m_compression_info > 7)
return {}; // non-deflate compression return {}; // non-deflate compression
if (zlib.m_has_dictionary) if (header.present_dictionary)
return {}; // we dont support pre-defined dictionaries return {}; // we dont support pre-defined dictionaries
if ((compression_info * 256 + flags) % 31 != 0) if (header.as_u16 % 31 != 0)
return {}; // error correction code doesn't match return {}; // error correction code doesn't match
zlib.m_data_bytes = data.slice(2, data.size() - 2 - 4); Zlib zlib { header, data };
zlib.m_data_bytes = data.slice(2, data.size() - sizeof(ZlibHeader) - Adler32Size);
return zlib; return zlib;
} }
Zlib::Zlib(ReadonlyBytes data) Zlib::Zlib(ZlibHeader header, ReadonlyBytes data)
: m_input_data(data) : m_header(header)
, m_input_data(data)
{ {
} }
@ -61,7 +56,7 @@ Optional<ByteBuffer> Zlib::decompress_all(ReadonlyBytes bytes)
u32 Zlib::checksum() u32 Zlib::checksum()
{ {
if (!m_checksum) { if (!m_checksum) {
auto bytes = m_input_data.slice(m_input_data.size() - 4, 4); auto bytes = m_input_data.slice_from_end(Adler32Size);
m_checksum = bytes.at(0) << 24 | bytes.at(1) << 16 | bytes.at(2) << 8 || bytes.at(3); m_checksum = bytes.at(0) << 24 | bytes.at(1) << 16 | bytes.at(2) << 8 || bytes.at(3);
} }

8
Userland/Libraries/LibCompress/Zlib.h
View file

@ -48,13 +48,9 @@ public:
static Optional<ByteBuffer> decompress_all(ReadonlyBytes); static Optional<ByteBuffer> decompress_all(ReadonlyBytes);
private: private:
Zlib(ReadonlyBytes data); Zlib(ZlibHeader, ReadonlyBytes data);
u8 m_compression_method; ZlibHeader m_header;
u8 m_compression_info;
u8 m_check_bits;
u8 m_has_dictionary;
u8 m_compression_level;
u32 m_checksum { 0 }; u32 m_checksum { 0 };
ReadonlyBytes m_input_data; ReadonlyBytes m_input_data;