Source
pub fn header(container: Container) []const u8 {
return switch (container) {
// GZIP 10 byte header (https://datatracker.ietf.org/doc/html/rfc1952#page-5):
// - ID1 (IDentification 1), always 0x1f
// - ID2 (IDentification 2), always 0x8b
// - CM (Compression Method), always 8 = deflate
// - FLG (Flags), all set to 0
// - 4 bytes, MTIME (Modification time), not used, all set to zero
// - XFL (eXtra FLags), all set to zero
// - OS (Operating System), 03 = Unix
.gzip => &[_]u8{ 0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x03 },
// ZLIB has a two-byte header (https://datatracker.ietf.org/doc/html/rfc1950#page-4):
// 1st byte:
// - First four bits is the CINFO (compression info), which is 7 for the default deflate window size.
// - The next four bits is the CM (compression method), which is 8 for deflate.
// 2nd byte:
// - Two bits is the FLEVEL (compression level). Values are: 0=fastest, 1=fast, 2=default, 3=best.
// - The next bit, FDICT, is set if a dictionary is given.
// - The final five FCHECK bits form a mod-31 checksum.
//
// CINFO = 7, CM = 8, FLEVEL = 0b10, FDICT = 0, FCHECK = 0b11100
.zlib => &[_]u8{ 0x78, 0b10_0_11100 },
.raw => &.{},
};
}