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[issues-1567] Add varint parsing #1568

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[issues-1567] Add varint parsing #1568

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73 changes: 73 additions & 0 deletions src/number/streaming.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1538,6 +1538,79 @@ where
}
}

#[inline]
#[doc(hidden)]
pub fn varint<I, E: ParseError<I>, R>(i: I) -> IResult<I, R, E>
where
I: Slice<RangeFrom<usize>> + InputIter<Item = u8> + InputLength + Copy,
R: std::ops::AddAssign<R> + std::ops::Shl<usize, Output = R> + Default + From<u8>,
{
let mut result = R::default();
let mut ofs: usize = 0;
let mut remainder = i;
loop {
let (i, byte) = le_u8(remainder)?;
result += (<R as From<u8>>::from(byte & 0x7F)) << ofs;
if byte < 0x80 {
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I believe this should exit if enough bytes for the target data type have been collected. Otherwise the right shift or addition will overflow.

return Ok((i, result));
}
remainder = i;
ofs += 7;
}
}

/// Recognizes a variable-length quantity.
///
/// *Streaming version*: Will return `Err(nom::Err::Incomplete(_))` if there is not enough data.
///
/// ```rust
/// # use nom::{Err, error::ErrorKind, Needed};
/// # use nom::Needed::Size;
/// use nom::number::streaming::varint_u128;
///
/// let parser = |s| {
/// varint_u128(s)
/// };
///
/// assert_eq!(parser(&[0x7F][..]), Ok((b"", 127)));
/// assert_eq!(parser(&[0x80][..]), Ok((b"", 128)));
/// assert_eq!(parser(&[0x20, 0x00][..]), Ok((b"", 8192)));
/// assert_eq!(parser(&[0x20, 0x00, 0x00][..]), Ok((b"", 2_097_152)));
/// ```
#[inline]
pub fn varint_u64<I, E: ParseError<I>>(i: I) -> IResult<I, u64, E>
where
I: Slice<RangeFrom<usize>> + InputIter<Item = u8> + InputLength + Copy,
{
varint::<I, E, u64>(i)
}

/// Recognizes a variable-length quantity.
///
/// *Streaming version*: Will return `Err(nom::Err::Incomplete(_))` if there is not enough data.
///
/// ```rust
/// # use nom::{Err, error::ErrorKind, Needed};
/// # use nom::Needed::Size;
/// use nom::number::streaming::varint_u128;
///
/// let parser = |s| {
/// varint_u128(s)
/// };
///
/// assert_eq!(parser(&[0x7F][..]), Ok((b"", 127)));
/// assert_eq!(parser(&[0x80][..]), Ok((b"", 128)));
/// assert_eq!(parser(&[0x20, 0x00][..]), Ok((b"", 8192)));
/// assert_eq!(parser(&[0x20, 0x00, 0x00][..]), Ok((b"", 2_097_152)));
/// ```
#[inline]
pub fn varint_u128<I, E: ParseError<I>>(i: I) -> IResult<I, u128, E>
where
I: Slice<RangeFrom<usize>> + InputIter<Item = u8> + InputLength + Copy,
{
varint::<I, E, u128>(i)
}

#[cfg(test)]
mod tests {
use super::*;
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