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LibCompress: Implement GZip compression

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This commit implements a stream compressor for the gzip
specification (RFC 1952), which is essentially a thin
wrapper around the DEFLATE compression format.
This commit is contained in:
Idan Horowitz 2021-03-13 01:26:44 +02:00 • committed by Andreas Kling
parent 02569bec11
commit 135751c3a2
2 changed files with 94 additions and 25 deletions
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59
Userland/Libraries/LibCompress/Gzip.cpp
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@ -1,5 +1,6 @@
/*
* Copyright (c) 2020, the SerenityOS developers.
* Copyright (c) 2021, Idan Horowitz <idan.horowitz@gmail.com>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
@ -36,12 +37,12 @@ bool GzipDecompressor::is_likely_compressed(ReadonlyBytes bytes)
return bytes.size() >= 2 && bytes[0] == gzip_magic_1 && bytes[1] == gzip_magic_2;
}
bool GzipDecompressor::BlockHeader::valid_magic_number() const
bool BlockHeader::valid_magic_number() const
{
return identification_1 == gzip_magic_1 && identification_2 == gzip_magic_2;
}
bool GzipDecompressor::BlockHeader::supported_by_implementation() const
bool BlockHeader::supported_by_implementation() const
{
if (compression_method != 0x08) {
// RFC 1952 does not define any compression methods other than deflate.
@ -187,4 +188,58 @@ Optional<ByteBuffer> GzipDecompressor::decompress_all(ReadonlyBytes bytes)
bool GzipDecompressor::unreliable_eof() const { return m_eof; }
GzipCompressor::GzipCompressor(OutputStream& stream)
: m_output_stream(stream)
{
}
GzipCompressor::~GzipCompressor()
{
}
size_t GzipCompressor::write(ReadonlyBytes bytes)
{
BlockHeader header;
header.identification_1 = 0x1f;
header.identification_2 = 0x8b;
header.compression_method = 0x08;
header.flags = 0;
header.modification_time = 0;
header.extra_flags = 3; // DEFLATE sets 2 for maximum compression and 4 for minimum compression
header.operating_system = 3; // unix
m_output_stream << Bytes { &header, sizeof(header) };
DeflateCompressor compressed_stream { m_output_stream };
VERIFY(compressed_stream.write_or_error(bytes));
compressed_stream.final_flush();
Crypto::Checksum::CRC32 crc32;
crc32.update(bytes);
LittleEndian<u32> digest = crc32.digest();
LittleEndian<u32> size = bytes.size();
m_output_stream << digest << size;
return bytes.size();
}
bool GzipCompressor::write_or_error(ReadonlyBytes bytes)
{
if (write(bytes) < bytes.size()) {
set_fatal_error();
return false;
}
return true;
}
Optional<ByteBuffer> GzipCompressor::compress_all(const ReadonlyBytes& bytes)
{
DuplexMemoryStream output_stream;
GzipCompressor gzip_stream { output_stream };
gzip_stream.write_or_error(bytes);
if (gzip_stream.handle_any_error())
return {};
return output_stream.copy_into_contiguous_buffer();
}
}