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v/vlib/compress/gzip/gzip.v

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// [rfc1952](https://datatracker.ietf.org/doc/html/rfc1952) compliant
// gzip compression/decompression
module gzip
import compress
import hash.crc32
// compresses an array of bytes using gzip and returns the compressed bytes in a new array
// Example: compressed := gzip.compress(b)?
pub fn compress(data []u8) ![]u8 {
compressed := compress.compress(data, 0)!
// header
mut result := [
u8(0x1f), // magic numbers (1F 8B)
0x8b,
0x08, // deflate
0x00, // header flags
0x00, // 4-byte timestamp, 0 = no timestamp (00 00 00 00)
0x00,
0x00,
0x00,
0x00, // extra flags
0xff, // operating system id (0xff = unknown)
] // 10 bytes
result << compressed
// trailer
checksum := crc32.sum(data)
length := data.len
result << [
u8(checksum >> 24),
u8(checksum >> 16),
u8(checksum >> 8),
u8(checksum),
u8(length >> 24),
u8(length >> 16),
u8(length >> 8),
u8(length),
] // 8 bytes
return result
}
[params]
pub struct DecompressParams {
verify_header_checksum bool = true
verify_length bool = true
verify_checksum bool = true
}
// decompresses an array of bytes using zlib and returns the decompressed bytes in a new array
// Example: decompressed := gzip.decompress(b)?
pub fn decompress(data []u8, params DecompressParams) ![]u8 {
if data.len < 18 {
return error('data is too short, not gzip compressed?')
} else if data[0] != 0x1f || data[1] != 0x8b {
return error('wrong magic numbers, not gzip compressed?')
} else if data[2] != 0x08 {
return error('gzip data is not compressed with DEFLATE')
}
mut header_length := 10
// parse flags, we ignore most of them, but we still need to parse them
// correctly, so we dont accidently decompress something that belongs
// to the header
if data[4] & 0b1110_0000 > 0 { // reserved bits
// rfc 1952 2.3.1.2 Compliance
// A compliant decompressor must give an error indication if any
// reserved bit is non-zero, since such a bit could indicate the
// presence of a new field that would cause subsequent data to be
// interpreted incorrectly.
return error('reserved flags are set, unsupported field detected')
}
// if data[4] & 0b0000_0001 {} // FTEXT
if data[4] & 0b0000_0100 > 0 { // FEXTRA, extra data
xlen := data[header_length]
header_length += xlen + 1
}
if data[4] & 0b0000_1000 > 0 { // FNAME, file name
// filename is zero-terminated, so skip until we hit a zero byte
for header_length < data.len && data[header_length] != 0x00 {
header_length++
}
header_length++
}
if data[4] & 0b0001_0000 > 0 { // FCOMMENT
// comment is zero-terminated, so skip until we hit a zero byte
for header_length < data.len && data[header_length] != 0x00 {
header_length++
}
header_length++
}
if data[4] & 0b0000_0010 > 0 { // FHCRC, flag header crc
if header_length + 12 > data.len {
return error('data too short')
}
checksum_header := crc32.sum(data[..header_length])
checksum_header_expected := (u32(data[header_length]) << 24) | (u32(data[header_length + 1]) << 16) | (u32(data[
header_length + 2]) << 8) | data[header_length + 3]
if params.verify_header_checksum && checksum_header != checksum_header_expected {
return error('header checksum verification failed')
}
header_length += 4
}
if header_length + 8 > data.len {
return error('data too short')
}
decompressed := compress.decompress(data[header_length..data.len - 8], 0)!
length_expected := (u32(data[data.len - 4]) << 24) | (u32(data[data.len - 3]) << 16) | (u32(data[data.len - 2]) << 8) | data[data.len - 1]
if params.verify_length && decompressed.len != length_expected {
return error('length verification failed, got $decompressed.len, expected $length_expected')
}
checksum := crc32.sum(decompressed)
checksum_expected := (u32(data[data.len - 8]) << 24) | (u32(data[data.len - 7]) << 16) | (u32(data[data.len - 6]) << 8) | data[data.len - 5]
if params.verify_checksum && checksum != checksum_expected {
return error('checksum verification failed')
}
return decompressed
}