Source code
Revision control
Copy as Markdown
Other Tools
//! Bit level parsers
//!
pub mod complete;
pub mod streaming;
use crate::error::{ErrorKind, ParseError};
use crate::internal::{Err, IResult, Needed, Parser};
use crate::lib::std::ops::RangeFrom;
use crate::traits::{ErrorConvert, Slice};
/// Converts a byte-level input to a bit-level input, for consumption by a parser that uses bits.
///
/// Afterwards, the input is converted back to a byte-level parser, with any remaining bits thrown
/// away.
///
/// # Example
/// ```
/// use nom::bits::{bits, streaming::take};
/// use nom::error::Error;
/// use nom::sequence::tuple;
/// use nom::IResult;
///
/// fn parse(input: &[u8]) -> IResult<&[u8], (u8, u8)> {
/// bits::<_, _, Error<(&[u8], usize)>, _, _>(tuple((take(4usize), take(8usize))))(input)
/// }
///
/// let input = &[0x12, 0x34, 0xff, 0xff];
///
/// let output = parse(input).expect("We take 1.5 bytes and the input is longer than 2 bytes");
///
/// // The first byte is consumed, the second byte is partially consumed and dropped.
/// let remaining = output.0;
/// assert_eq!(remaining, [0xff, 0xff]);
///
/// let parsed = output.1;
/// assert_eq!(parsed.0, 0x01);
/// assert_eq!(parsed.1, 0x23);
/// ```
pub fn bits<I, O, E1, E2, P>(mut parser: P) -> impl FnMut(I) -> IResult<I, O, E2>
where
E1: ParseError<(I, usize)> + ErrorConvert<E2>,
E2: ParseError<I>,
I: Slice<RangeFrom<usize>>,
P: Parser<(I, usize), O, E1>,
{
move |input: I| match parser.parse((input, 0)) {
Ok(((rest, offset), result)) => {
// If the next byte has been partially read, it will be sliced away as well.
// The parser functions might already slice away all fully read bytes.
// That's why `offset / 8` isn't necessarily needed at all times.
let remaining_bytes_index = offset / 8 + if offset % 8 == 0 { 0 } else { 1 };
Ok((rest.slice(remaining_bytes_index..), result))
}
Err(Err::Incomplete(n)) => Err(Err::Incomplete(n.map(|u| u.get() / 8 + 1))),
Err(Err::Error(e)) => Err(Err::Error(e.convert())),
Err(Err::Failure(e)) => Err(Err::Failure(e.convert())),
}
}
/// Counterpart to `bits`, `bytes` transforms its bit stream input into a byte slice for the underlying
/// parser, allowing byte-slice parsers to work on bit streams.
///
/// A partial byte remaining in the input will be ignored and the given parser will start parsing
/// at the next full byte.
///
/// ```
/// use nom::bits::{bits, bytes, streaming::take};
/// use nom::combinator::rest;
/// use nom::error::Error;
/// use nom::sequence::tuple;
/// use nom::IResult;
///
/// fn parse(input: &[u8]) -> IResult<&[u8], (u8, u8, &[u8])> {
/// bits::<_, _, Error<(&[u8], usize)>, _, _>(tuple((
/// take(4usize),
/// take(8usize),
/// bytes::<_, _, Error<&[u8]>, _, _>(rest)
/// )))(input)
/// }
///
/// let input = &[0x12, 0x34, 0xff, 0xff];
///
/// assert_eq!(parse( input ), Ok(( &[][..], (0x01, 0x23, &[0xff, 0xff][..]) )));
/// ```
pub fn bytes<I, O, E1, E2, P>(mut parser: P) -> impl FnMut((I, usize)) -> IResult<(I, usize), O, E2>
where
E1: ParseError<I> + ErrorConvert<E2>,
E2: ParseError<(I, usize)>,
I: Slice<RangeFrom<usize>> + Clone,
P: Parser<I, O, E1>,
{
move |(input, offset): (I, usize)| {
let inner = if offset % 8 != 0 {
input.slice((1 + offset / 8)..)
} else {
input.slice((offset / 8)..)
};
let i = (input, offset);
match parser.parse(inner) {
Ok((rest, res)) => Ok(((rest, 0), res)),
Err(Err::Incomplete(Needed::Unknown)) => Err(Err::Incomplete(Needed::Unknown)),
Err(Err::Incomplete(Needed::Size(sz))) => Err(match sz.get().checked_mul(8) {
Some(v) => Err::Incomplete(Needed::new(v)),
None => Err::Failure(E2::from_error_kind(i, ErrorKind::TooLarge)),
}),
Err(Err::Error(e)) => Err(Err::Error(e.convert())),
Err(Err::Failure(e)) => Err(Err::Failure(e.convert())),
}
}
}
#[cfg(test)]
mod test {
use super::*;
use crate::bits::streaming::take;
use crate::error::Error;
use crate::sequence::tuple;
#[test]
/// Take the `bits` function and assert that remaining bytes are correctly returned, if the
/// previous bytes are fully consumed
fn test_complete_byte_consumption_bits() {
let input = &[0x12, 0x34, 0x56, 0x78];
// Take 3 bit slices with sizes [4, 8, 4].
let result: IResult<&[u8], (u8, u8, u8)> =
bits::<_, _, Error<(&[u8], usize)>, _, _>(tuple((take(4usize), take(8usize), take(4usize))))(
input,
);
let output = result.expect("We take 2 bytes and the input is longer than 2 bytes");
let remaining = output.0;
assert_eq!(remaining, [0x56, 0x78]);
let parsed = output.1;
assert_eq!(parsed.0, 0x01);
assert_eq!(parsed.1, 0x23);
assert_eq!(parsed.2, 0x04);
}
#[test]
/// Take the `bits` function and assert that remaining bytes are correctly returned, if the
/// previous bytes are NOT fully consumed. Partially consumed bytes are supposed to be dropped.
/// I.e. if we consume 1.5 bytes of 4 bytes, 2 bytes will be returned, bits 13-16 will be
/// dropped.
fn test_partial_byte_consumption_bits() {
let input = &[0x12, 0x34, 0x56, 0x78];
// Take bit slices with sizes [4, 8].
let result: IResult<&[u8], (u8, u8)> =
bits::<_, _, Error<(&[u8], usize)>, _, _>(tuple((take(4usize), take(8usize))))(input);
let output = result.expect("We take 1.5 bytes and the input is longer than 2 bytes");
let remaining = output.0;
assert_eq!(remaining, [0x56, 0x78]);
let parsed = output.1;
assert_eq!(parsed.0, 0x01);
assert_eq!(parsed.1, 0x23);
}
#[test]
#[cfg(feature = "std")]
/// Ensure that in Incomplete error is thrown, if too few bytes are passed for a given parser.
fn test_incomplete_bits() {
let input = &[0x12];
// Take bit slices with sizes [4, 8].
let result: IResult<&[u8], (u8, u8)> =
bits::<_, _, Error<(&[u8], usize)>, _, _>(tuple((take(4usize), take(8usize))))(input);
assert!(result.is_err());
let error = result.err().unwrap();
assert_eq!("Parsing requires 2 bytes/chars", error.to_string());
}
}