1 /// Generate a random frame mask.
2 #[inline]
generate_mask() -> [u8; 4]3 pub fn generate_mask() -> [u8; 4] {
4 rand::random()
5 }
6
7 /// Mask/unmask a frame.
8 #[inline]
apply_mask(buf: &mut [u8], mask: [u8; 4])9 pub fn apply_mask(buf: &mut [u8], mask: [u8; 4]) {
10 apply_mask_fast32(buf, mask)
11 }
12
13 /// A safe unoptimized mask application.
14 #[inline]
apply_mask_fallback(buf: &mut [u8], mask: [u8; 4])15 fn apply_mask_fallback(buf: &mut [u8], mask: [u8; 4]) {
16 for (i, byte) in buf.iter_mut().enumerate() {
17 *byte ^= mask[i & 3];
18 }
19 }
20
21 /// Faster version of `apply_mask()` which operates on 4-byte blocks.
22 #[inline]
apply_mask_fast32(buf: &mut [u8], mask: [u8; 4])23 pub fn apply_mask_fast32(buf: &mut [u8], mask: [u8; 4]) {
24 let mask_u32 = u32::from_ne_bytes(mask);
25
26 let (prefix, words, suffix) = unsafe { buf.align_to_mut::<u32>() };
27 apply_mask_fallback(prefix, mask);
28 let head = prefix.len() & 3;
29 let mask_u32 = if head > 0 {
30 if cfg!(target_endian = "big") {
31 mask_u32.rotate_left(8 * head as u32)
32 } else {
33 mask_u32.rotate_right(8 * head as u32)
34 }
35 } else {
36 mask_u32
37 };
38 for word in words.iter_mut() {
39 *word ^= mask_u32;
40 }
41 apply_mask_fallback(suffix, mask_u32.to_ne_bytes());
42 }
43
44 #[cfg(test)]
45 mod tests {
46 use super::*;
47
48 #[test]
test_apply_mask()49 fn test_apply_mask() {
50 let mask = [0x6d, 0xb6, 0xb2, 0x80];
51 let unmasked = [
52 0xf3, 0x00, 0x01, 0x02, 0x03, 0x80, 0x81, 0x82, 0xff, 0xfe, 0x00, 0x17, 0x74, 0xf9,
53 0x12, 0x03,
54 ];
55
56 for data_len in 0..=unmasked.len() {
57 let unmasked = &unmasked[0..data_len];
58 // Check masking with different alignment.
59 for off in 0..=3 {
60 if unmasked.len() < off {
61 continue;
62 }
63 let mut masked = unmasked.to_vec();
64 apply_mask_fallback(&mut masked[off..], mask);
65
66 let mut masked_fast = unmasked.to_vec();
67 apply_mask_fast32(&mut masked_fast[off..], mask);
68
69 assert_eq!(masked, masked_fast);
70 }
71 }
72 }
73 }
74