nom_varint/
lib.rs

1//! # nom-varint
2//!
3//! Parse varints (used by Minecraft, Celeste, and Protocol Buffers) using nom.
4
5#![no_std]
6
7use core::convert::TryInto;
8use core::u32;
9use nom::bytes::complete::take;
10use nom::error::{ErrorKind, ParseError};
11use nom::Err::*;
12use nom::Needed::Unknown;
13
14/// Parses a varint.
15///
16/// # Examples
17///
18/// ```
19/// assert_eq!(nom_varint::take_varint::<()>(&[0x0b]), Ok((&[] as &[u8], 0x0b)));
20/// ```
21pub fn take_varint<'a, E>(i: &'a [u8]) -> nom::IResult<&'a [u8], usize, E>
22where
23    E: ParseError<&'a [u8]>,
24{
25    let mut res: usize = 0;
26    let mut count: usize = 0;
27    let mut remainder = i;
28    loop {
29        let byte = match take::<usize, &[u8], ()>(1)(remainder) {
30            Ok((rest, bytes)) => {
31                remainder = rest;
32                bytes[0]
33            }
34            Err(_) => return Err(Incomplete(Unknown)),
35        };
36        res += ((byte as usize) & 127)
37            .checked_shl((count * 7).try_into().unwrap_or(u32::MAX))
38            .ok_or_else(|| Error(E::from_error_kind(remainder, ErrorKind::MapOpt)))?;
39        count += 1;
40        if (byte >> 7) == 0 {
41            return Ok((remainder, res));
42        }
43    }
44}
45
46#[cfg(test)]
47mod test {
48    #[test]
49    fn parse_varint_simple() {
50        assert_eq!(
51            super::take_varint::<()>(&[0x0b, 0x01, 0x02, 0x03]),
52            Ok((b"\x01\x02\x03" as &[u8], 11))
53        );
54    }
55
56    #[test]
57    fn parse_varint_twobyte() {
58        assert_eq!(
59            super::take_varint::<()>(&[0x84, 0x02, 0x04, 0x05, 0x06]),
60            Ok((b"\x04\x05\x06" as &[u8], 260))
61        );
62    }
63}
nom_varint/lib.rs

nom_varint/
lib.rs
