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gzip: fix flag location in header (#17140)

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anusrnm 2023-01-29 16:57:04 +05:30 committed by GitHub
parent 7f5f69a78a
commit 5cd01ea494
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2 changed files with 65 additions and 33 deletions
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82
vlib/compress/gzip/gzip.v
View File

@ -47,23 +47,44 @@ pub struct DecompressParams {
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 {
pub const (
reserved_bits = 0b1110_0000
ftext = 0b0000_0001
fextra = 0b0000_0100
fname = 0b0000_1000
fcomment = 0b0001_0000
fhcrc = 0b0000_0010
)
const min_header_length = 18
[noinit]
pub struct GzipHeader {
pub mut:
length int = 10
extra []u8
filename []u8
comment []u8
modification_time u32
operating_system u8
}
// validate validates the header and returns its details if valid
pub fn validate(data []u8, params DecompressParams) !GzipHeader {
if data.len < gzip.min_header_length {
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
mut header := GzipHeader{}
// 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
if data[3] & gzip.reserved_bits > 0 {
// 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
@ -72,40 +93,51 @@ pub fn decompress(data []u8, params DecompressParams) ![]u8 {
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[3] & gzip.fextra > 0 {
xlen := data[header.length]
header.extra = data[header.length + 1..header.length + 1 + xlen]
header.length += xlen + 1
}
if data[4] & 0b0000_1000 > 0 { // FNAME, file name
if data[3] & gzip.fname > 0 {
// filename is zero-terminated, so skip until we hit a zero byte
for header_length < data.len && data[header_length] != 0x00 {
header_length++
for header.length < data.len && data[header.length] != 0x00 {
header.filename << data[header.length]
header.length++
}
header_length++
header.length++
}
if data[4] & 0b0001_0000 > 0 { // FCOMMENT
if data[3] & gzip.fcomment > 0 {
// comment is zero-terminated, so skip until we hit a zero byte
for header_length < data.len && data[header_length] != 0x00 {
header_length++
for header.length < data.len && data[header.length] != 0x00 {
header.comment << data[header.length]
header.length++
}
header_length++
header.length++
}
if data[4] & 0b0000_0010 > 0 { // FHCRC, flag header crc
if header_length + 12 > data.len {
if data[3] & gzip.fhcrc > 0 {
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]
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
header.length += 4
}
if header_length + 8 > data.len {
if header.length + 8 > data.len {
return error('data too short')
}
header.operating_system = data[9]
return header
}
// 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 {
gzip_header := validate(data, params)!
header_length := gzip_header.length
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]

16
vlib/compress/gzip/gzip_test.v
View File

@ -35,7 +35,7 @@ fn test_gzip_invalid_compression() {
fn test_gzip_with_ftext() {
uncompressed := 'Hello world!'
mut compressed := compress(uncompressed.bytes())!
compressed[4] |= 0b0000_0001 // FTEXT
compressed[3] |= ftext
decompressed := decompress(compressed)!
assert decompressed == uncompressed.bytes()
}
@ -43,7 +43,7 @@ fn test_gzip_with_ftext() {
fn test_gzip_with_fname() {
uncompressed := 'Hello world!'
mut compressed := compress(uncompressed.bytes())!
compressed[4] |= 0b0000_1000
compressed[3] |= fname
compressed.insert(10, `h`)
compressed.insert(11, `i`)
compressed.insert(12, 0x00)
@ -54,7 +54,7 @@ fn test_gzip_with_fname() {
fn test_gzip_with_fcomment() {
uncompressed := 'Hello world!'
mut compressed := compress(uncompressed.bytes())!
compressed[4] |= 0b0001_0000
compressed[3] |= fcomment
compressed.insert(10, `h`)
compressed.insert(11, `i`)
compressed.insert(12, 0x00)
@ -65,7 +65,7 @@ fn test_gzip_with_fcomment() {
fn test_gzip_with_fname_fcomment() {
uncompressed := 'Hello world!'
mut compressed := compress(uncompressed.bytes())!
compressed[4] |= 0b0001_1000
compressed[3] |= (fname | fcomment)
compressed.insert(10, `h`)
compressed.insert(11, `i`)
compressed.insert(12, 0x00)
@ -79,7 +79,7 @@ fn test_gzip_with_fname_fcomment() {
fn test_gzip_with_fextra() {
uncompressed := 'Hello world!'
mut compressed := compress(uncompressed.bytes())!
compressed[4] |= 0b0000_0100
compressed[3] |= fextra
compressed.insert(10, 2)
compressed.insert(11, `h`)
compressed.insert(12, `i`)
@ -90,7 +90,7 @@ fn test_gzip_with_fextra() {
fn test_gzip_with_hcrc() {
uncompressed := 'Hello world!'
mut compressed := compress(uncompressed.bytes())!
compressed[4] |= 0b0000_0010
compressed[3] |= fhcrc
checksum := crc32.sum(compressed[..10])
compressed.insert(10, u8(checksum >> 24))
compressed.insert(11, u8(checksum >> 16))
@ -103,7 +103,7 @@ fn test_gzip_with_hcrc() {
fn test_gzip_with_invalid_hcrc() {
uncompressed := 'Hello world!'
mut compressed := compress(uncompressed.bytes())!
compressed[4] |= 0b0000_0010
compressed[3] |= fhcrc
checksum := crc32.sum(compressed[..10])
compressed.insert(10, u8(checksum >> 24))
compressed.insert(11, u8(checksum >> 16))
@ -129,6 +129,6 @@ fn test_gzip_with_invalid_length() {
fn test_gzip_with_invalid_flags() {
uncompressed := 'Hello world!'
mut compressed := compress(uncompressed.bytes())!
compressed[4] |= 0b1000_0000
compressed[3] |= 0b1000_0000
assert_decompress_error(compressed, 'reserved flags are set, unsupported field detected')!
}