compress: change the endian for validation to conform to the gzip file specification(fix #19839)

vlib/compress/gzip/gzip.v

@@ -28,14 +28,14 @@ pub fn compress(data []u8) ![]u8 {
 	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(checksum >> 8),
+		u8(checksum >> 16),
+		u8(checksum >> 24),
 		u8(length),
+		u8(length >> 8),
+		u8(length >> 16),
+		u8(length >> 24),
 	] // 8 bytes
 	return result
 }
@@ -140,12 +140,12 @@ pub fn decompress(data []u8, params DecompressParams) ![]u8 {
 	header_length := gzip_header.length
 
 	decompressed := compr.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]
+	length_expected := (u32(data[data.len - 1]) << 24) | (u32(data[data.len - 2]) << 16) | (u32(data[data.len - 3]) << 8) | data[data.len - 4]
 	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]
+	checksum_expected := (u32(data[data.len - 5]) << 24) | (u32(data[data.len - 6]) << 16) | (u32(data[data.len - 7]) << 8) | data[data.len - 8]
 	if params.verify_checksum && checksum != checksum_expected {
 		return error('checksum verification failed')
 	}

vlib/compress/gzip/gzip_test.v

@@ -123,7 +123,7 @@ fn test_gzip_with_invalid_length() {
 	uncompressed := 'Hello world!'
 	mut compressed := compress(uncompressed.bytes())!
 	compressed[compressed.len - 1] += 1
-	assert_decompress_error(compressed, 'length verification failed, got 12, expected 13')!
+	assert_decompress_error(compressed, 'length verification failed, got 12, expected 16777228')!
 }
 
 fn test_gzip_with_invalid_flags() {

vlib/compress/gzip/read_gz_files_test.v

@@ -0,0 +1,41 @@
+import os
+import compress.gzip
+
+const samples_folder = os.join_path(os.dir(@FILE), 'samples')
+
+fn s(fname string) string {
+	return os.join_path(samples_folder, fname)
+}
+
+fn read_and_decode_file(fpath string) !([]u8, string) {
+	compressed := os.read_bytes(fpath)!
+	decoded := gzip.decompress(compressed)!
+	content := decoded.bytestr()
+	return compressed, content
+}
+
+fn test_reading_and_decoding_a_known_gziped_file() {
+	compressed, content := read_and_decode_file(s('known.gz'))!
+	assert compressed#[0..3] == [u8(31), 139, 8]
+	assert compressed#[-5..] == [u8(127), 115, 1, 0, 0]
+	assert content.contains('## Description:')
+	assert content.contains('## Examples:')
+	assert content.ends_with('```\n')
+}
+
+fn test_decoding_all_samples_files() {
+	for gz_file in os.walk_ext(samples_folder, '.gz') {
+		_, content := read_and_decode_file(gz_file)!
+		assert content.len > 0, 'decoded content should not be empty: `${content}`'
+	}
+}
+
+fn test_reading_gzip_files_compressed_with_different_options() {
+	_, content1 := read_and_decode_file(s('readme_level_1.gz'))!
+	_, content5 := read_and_decode_file(s('readme_level_5.gz'))!
+	_, content9 := read_and_decode_file(s('readme_level_9.gz'))!
+	_, content9_rsyncable := read_and_decode_file(s('readme_level_9_rsyncable.gz'))!
+	assert content9_rsyncable == content9
+	assert content9 == content5
+	assert content5 == content1
+}