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LibCompress: Use LZMA context from preexisting dictionary

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Tim Schumacher 2023-03-29 18:15:44 +02:00 committed by Andreas Kling
parent c020ee8bfa
commit fe761a4e9b
2 changed files with 59 additions and 1 deletions
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58
Tests/LibCompress/TestXz.cpp
View file

@ -120,6 +120,64 @@ TEST_CASE(lzma2_uncompressed_size_overflow)
EXPECT(buffer_or_error.is_error());
}
TEST_CASE(lzma2_literal_context_bits_after_state_reset)
{
Array<u8, 72> const compressed {
// Stream Header
0xFD, 0x37, 0x7A, 0x58, 0x5A, 0x00, // Magic
0x00, 0x00, // Stream Flags (Check: None)
0xFF, 0x12, 0xD9, 0x41, // CRC32
// Block Header
0x02, // Block Header Size [(0x02 + 1) * 4, i.e. 12 bytes]
0x00, // Block Flags (one filter, no compressed or uncompressed size present)
// Filter 0 Flags
0x21, // Filter ID (0x21 for LZMA2, encoded as a multibyte integer)
0x01, // Size of Properties (0x01, encoded as a multibyte integer)
0x00, // Filter Properties (LZMA2 encoded dictionary size byte; 0x00 = 4 KiB)
0x00, 0x00, 0x00, // Header Padding
0x37, 0x27, 0x97, 0xD6, // CRC32
// Compressed Data (LZMA2)
// LZMA chunk with dictionary reset
0xE0, // Control Byte
0x00, 0x00, // Low 16 bits of uncompressed size minus one (big-endian)
0x00, 0x05, // Compressed size minus one (big-endian)
0x01, // LZMA properties byte (lc = 1; lp = 0; pb = 0)
0x00, 0x3F, 0xFF, 0xFC, 0x00, 0x00,
// LZMA chunk with state reset
0xA0, // Control Byte
0x00, 0x01, // Low 16 bits of uncompressed size minus one (big-endian)
0x00, 0x06, // Compressed size minus one (big-endian)
0x00, 0x40, 0x1F, 0xF4, 0x00, 0x00, 0x00,
// End of LZMA2 stream
0x00,
// Block Padding
0x00, 0x00, 0x00,
// Index
0x00, // Index Indicator
0x01, // Number of Records (multibyte integer)
// Record 0
0x25, // Unpadded Size (multibyte integer)
0x03, // Uncompressed Size (multibyte integer)
// CRC32
0x76, 0x34, 0x7C, 0x51,
// Stream Footer
0x06, 0x72, 0x9E, 0x7A, // CRC32
0x01, 0x00, 0x00, 0x00, // Backward Size
0x00, 0x00, // Stream Flags
0x59, 0x5A, // Footer Magic Bytes
};
auto stream = MUST(try_make<FixedMemoryStream>(compressed));
auto decompressor = MUST(Compress::XzDecompressor::create(move(stream)));
auto buffer = MUST(decompressor->read_until_eof(PAGE_SIZE));
EXPECT_EQ("\x80\x80\x80"sv.bytes(), buffer.span());
}
// The following tests are based on test files from the XZ utils package, which have been placed in the public domain:
// https://tukaani.org/xz/xz-5.4.1.tar.xz (subdirectory /xz-5.4.1/tests/files)
// Test descriptions have been taken from the README file in the test files directory.

2
Userland/Libraries/LibCompress/Lzma.cpp
View file

@ -295,7 +295,7 @@ ErrorOr<u16> LzmaDecompressor::decode_symbol_using_reverse_bit_tree(size_t bit_c
ErrorOr<void> LzmaDecompressor::decode_literal_to_output_buffer()
{
u8 previous_byte = 0;
if (m_total_decoded_bytes > 0) {
if (m_dictionary->seekback_limit() > 0) {
auto read_bytes = MUST(m_dictionary->read_with_seekback({ &previous_byte, sizeof(previous_byte) }, 1));
VERIFY(read_bytes.size() == sizeof(previous_byte));
}