protobuf/varint/
decode.rs

Help
1//! Varint decode utilities.
2
3use crate::error::WireError;
4use crate::varint::MAX_VARINT32_ENCODED_LEN;
5use crate::varint::MAX_VARINT_ENCODED_LEN;
6
7trait DecodeVarint {
8    const MAX_ENCODED_LEN: usize;
9    const LAST_BYTE_MAX_VALUE: u8;
10
11    fn from_u64(value: u64) -> Self;
12}
13
14impl DecodeVarint for u64 {
15    const MAX_ENCODED_LEN: usize = MAX_VARINT_ENCODED_LEN;
16    const LAST_BYTE_MAX_VALUE: u8 = 0x01;
17
18    fn from_u64(value: u64) -> Self {
19        value
20    }
21}
22
23impl DecodeVarint for u32 {
24    const MAX_ENCODED_LEN: usize = MAX_VARINT32_ENCODED_LEN;
25    const LAST_BYTE_MAX_VALUE: u8 = 0x0f;
26
27    fn from_u64(value: u64) -> Self {
28        value as u32
29    }
30}
31
32/// Decode a varint, and return decoded value and decoded byte count.
33#[inline]
34fn decode_varint_full<D: DecodeVarint>(rem: &[u8]) -> crate::Result<Option<(D, usize)>> {
35    let mut r: u64 = 0;
36    for (i, &b) in rem.iter().enumerate() {
37        if i == D::MAX_ENCODED_LEN - 1 {
38            if b > D::LAST_BYTE_MAX_VALUE {
39                return Err(WireError::IncorrectVarint.into());
40            }
41            let r = r | ((b as u64) << (i as u64 * 7));
42            return Ok(Some((D::from_u64(r), i + 1)));
43        }
44
45        r = r | (((b & 0x7f) as u64) << (i as u64 * 7));
46        if b < 0x80 {
47            return Ok(Some((D::from_u64(r), i + 1)));
48        }
49    }
50    Ok(None)
51}
52
53#[inline]
54fn decode_varint_impl<D: DecodeVarint>(buf: &[u8]) -> crate::Result<Option<(D, usize)>> {
55    if buf.len() >= 1 && buf[0] < 0x80 {
56        // The the most common case.
57        let ret = buf[0] as u64;
58        let consume = 1;
59        Ok(Some((D::from_u64(ret), consume)))
60    } else if buf.len() >= 2 && buf[1] < 0x80 {
61        // Handle the case of two bytes too.
62        let ret = (buf[0] & 0x7f) as u64 | (buf[1] as u64) << 7;
63        let consume = 2;
64        Ok(Some((D::from_u64(ret), consume)))
65    } else {
66        // Read from array when buf at at least 10 bytes,
67        // max len for varint.
68        decode_varint_full(buf)
69    }
70}
71
72/// Try decode a varint. Return `None` if the buffer does not contain complete varint.
73#[inline]
74pub(crate) fn decode_varint64(buf: &[u8]) -> crate::Result<Option<(u64, usize)>> {
75    decode_varint_impl(buf)
76}
77
78/// Try decode a varint. Return `None` if the buffer does not contain complete varint.
79#[inline]
80pub(crate) fn decode_varint32(buf: &[u8]) -> crate::Result<Option<(u32, usize)>> {
81    decode_varint_impl(buf)
82}
83
84#[cfg(test)]
85mod tests {
86    use crate::hex::decode_hex;
87    use crate::varint::decode::decode_varint32;
88    use crate::varint::decode::decode_varint64;
89
90    #[test]
91    fn test_decode_varint64() {
92        assert_eq!((0, 1), decode_varint64(&decode_hex("00")).unwrap().unwrap());
93        assert_eq!(
94            (u64::MAX, 10),
95            decode_varint64(&decode_hex("ff ff ff ff ff ff ff ff ff 01"))
96                .unwrap()
97                .unwrap()
98        );
99        assert!(decode_varint64(&decode_hex("ff ff ff ff ff ff ff ff ff 02")).is_err());
100    }
101
102    #[test]
103    fn test_decode_varint32() {
104        assert_eq!((0, 1), decode_varint32(&decode_hex("00")).unwrap().unwrap());
105        assert_eq!(
106            (u32::MAX, 5),
107            decode_varint32(&decode_hex("ff ff ff ff 0f"))
108                .unwrap()
109                .unwrap()
110        );
111        assert!(decode_varint32(&decode_hex("ff ff ff ff 10")).is_err());
112    }
113}
protobuf/varint/decode.rs

protobuf/varint/
decode.rs
