# Function nom::multi::length_value

source · [−]

    pub fn length_value<I, O, N, E, F, G>(
        f: F,
        g: G
    ) -> impl FnMut(I) -> IResult<I, O, E> where
        I: Clone + InputLength + InputTake,
        N: ToUsize,
        F: Parser<I, N, E>,
        G: Parser<I, O, E>,
        E: ParseError<I>,

Expand description

Gets a number from the first parser, takes a subslice of the input of that size, then applies the second parser on that subslice. If the second parser returns `Incomplete`, `length_value` will return an error.

## Arguments

- `f` The parser to apply.
- `g` The parser to apply on the subslice.

    use nom::number::complete::be_u16;
    use nom::multi::length_value;
    use nom::bytes::complete::tag;

    fn parser(s: &[u8]) -> IResult<&[u8], &[u8]> {
      length_value(be_u16, tag("abc"))(s)
    }

    assert_eq!(parser(b"\x00\x03abcefg"), Ok((&b"efg"[..], &b"abc"[..])));
    assert_eq!(parser(b"\x00\x03123123"), Err(Err::Error(Error::new(&b"123"[..], ErrorKind::Tag))));
    assert_eq!(parser(b"\x00\x03a"), Err(Err::Incomplete(Needed::new(2))));