httproxide_h3/qpack/
prefix_int.rs

1use std::fmt;
2
3use bytes::{Buf, BufMut};
4
5use crate::proto::coding::{self, BufExt, BufMutExt};
6
7#[derive(Debug, PartialEq)]
8pub enum Error {
9    Overflow,
10    UnexpectedEnd,
11}
12
13impl std::fmt::Display for Error {
14    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> fmt::Result {
15        match self {
16            Error::Overflow => write!(f, "value overflow"),
17            Error::UnexpectedEnd => write!(f, "unexpected end"),
18        }
19    }
20}
21
22pub fn decode<B: Buf>(size: u8, buf: &mut B) -> Result<(u8, usize), Error> {
23    assert!(size <= 8);
24    let mut first = buf.get::<u8>()?;
25
26    // NOTE: following casts to u8 intend to trim the most significant bits, they are used as a
27    //       workaround for shiftoverflow errors when size == 8.
28    let flags = ((first as usize) >> size) as u8;
29    let mask = 0xFF >> (8 - size);
30    first &= mask;
31
32    // if first < 2usize.pow(size) - 1
33    if first < mask {
34        return Ok((flags, first as usize));
35    }
36
37    let mut value = mask as usize;
38    let mut power = 0usize;
39    loop {
40        let byte = buf.get::<u8>()? as usize;
41        value += (byte & 127) << power;
42        power += 7;
43
44        if byte & 128 == 0 {
45            break;
46        }
47
48        if power >= MAX_POWER {
49            return Err(Error::Overflow);
50        }
51    }
52
53    Ok((flags, value))
54}
55
56pub fn encode<B: BufMut>(size: u8, flags: u8, value: usize, buf: &mut B) {
57    assert!(size <= 8);
58    // NOTE: following casts to u8 intend to trim the most significant bits, they are used as a
59    //       workaround for shiftoverflow errors when size == 8.
60    let mask = !(0xFF << size) as u8;
61    let flags = ((flags as usize) << size) as u8;
62
63    // if value < 2usize.pow(size) - 1
64    if value < (mask as usize) {
65        buf.write(flags | value as u8);
66        return;
67    }
68
69    buf.write(mask | flags);
70    let mut remaining = value - mask as usize;
71
72    while remaining >= 128 {
73        let rest = (remaining % 128) as u8;
74        buf.write(rest + 128);
75        remaining /= 128;
76    }
77    buf.write(remaining as u8);
78}
79
80#[cfg(target_pointer_width = "64")]
81const MAX_POWER: usize = 10 * 7;
82
83#[cfg(target_pointer_width = "32")]
84const MAX_POWER: usize = 5 * 7;
85
86impl From<coding::UnexpectedEnd> for Error {
87    fn from(_: coding::UnexpectedEnd) -> Self {
88        Error::UnexpectedEnd
89    }
90}
91
92#[cfg(test)]
93mod test {
94    use std::io::Cursor;
95
96    fn check_codec(size: u8, flags: u8, value: usize, data: &[u8]) {
97        let mut buf = Vec::new();
98        super::encode(size, flags, value, &mut buf);
99        assert_eq!(buf, data);
100        let mut read = Cursor::new(&buf);
101        assert_eq!((flags, value), super::decode(size, &mut read).unwrap());
102    }
103
104    #[test]
105    fn codec_5_bits() {
106        check_codec(5, 0b101, 10, &[0b1010_1010]);
107        check_codec(5, 0b101, 0, &[0b1010_0000]);
108        check_codec(5, 0b010, 1337, &[0b0101_1111, 154, 10]);
109        check_codec(5, 0b010, 31, &[0b0101_1111, 0]);
110        check_codec(
111            5,
112            0b010,
113            usize::max_value(),
114            &[95, 224, 255, 255, 255, 255, 255, 255, 255, 255, 1],
115        );
116    }
117
118    #[test]
119    fn codec_8_bits() {
120        check_codec(8, 0, 42, &[0b0010_1010]);
121        check_codec(8, 0, 424_242, &[255, 179, 240, 25]);
122        check_codec(
123            8,
124            0,
125            usize::max_value(),
126            &[255, 128, 254, 255, 255, 255, 255, 255, 255, 255, 1],
127        );
128    }
129
130    #[test]
131    #[should_panic]
132    fn size_too_big_value() {
133        let mut buf = vec![];
134        super::encode(9, 1, 1, &mut buf);
135    }
136
137    #[test]
138    #[should_panic]
139    fn size_too_big_of_size() {
140        let buf = vec![];
141        let mut read = Cursor::new(&buf);
142        super::decode(9, &mut read).unwrap();
143    }
144
145    #[cfg(target_pointer_width = "64")]
146    #[test]
147    fn overflow() {
148        let buf = vec![255, 128, 254, 255, 255, 255, 255, 255, 255, 255, 255, 1];
149        let mut read = Cursor::new(&buf);
150        assert!(super::decode(8, &mut read).is_err());
151    }
152
153    #[test]
154    fn number_never_ends_with_0x80() {
155        check_codec(4, 0b0001, 143, &[31, 128, 1]);
156    }
157}
httproxide_h3/qpack/prefix_int.rs

httproxide_h3/qpack/
prefix_int.rs
