nom/bits/
mod.rs

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1//! Bit level parsers
2//!
3
4pub mod complete;
5pub mod streaming;
6
7use crate::error::{ErrorKind, ParseError};
8use crate::internal::{Err, IResult, Needed, Parser};
9use crate::lib::std::ops::RangeFrom;
10use crate::traits::{ErrorConvert, Slice};
11
12/// Converts a byte-level input to a bit-level input, for consumption by a parser that uses bits.
13///
14/// Afterwards, the input is converted back to a byte-level parser, with any remaining bits thrown
15/// away.
16///
17/// # Example
18/// ```
19/// use nom::bits::{bits, streaming::take};
20/// use nom::error::Error;
21/// use nom::sequence::tuple;
22/// use nom::IResult;
23///
24/// fn parse(input: &[u8]) -> IResult<&[u8], (u8, u8)> {
25///     bits::<_, _, Error<(&[u8], usize)>, _, _>(tuple((take(4usize), take(8usize))))(input)
26/// }
27///
28/// let input = &[0x12, 0x34, 0xff, 0xff];
29///
30/// let output = parse(input).expect("We take 1.5 bytes and the input is longer than 2 bytes");
31///
32/// // The first byte is consumed, the second byte is partially consumed and dropped.
33/// let remaining = output.0;
34/// assert_eq!(remaining, [0xff, 0xff]);
35///
36/// let parsed = output.1;
37/// assert_eq!(parsed.0, 0x01);
38/// assert_eq!(parsed.1, 0x23);
39/// ```
40pub fn bits<I, O, E1, E2, P>(mut parser: P) -> impl FnMut(I) -> IResult<I, O, E2>
41where
42  E1: ParseError<(I, usize)> + ErrorConvert<E2>,
43  E2: ParseError<I>,
44  I: Slice<RangeFrom<usize>>,
45  P: Parser<(I, usize), O, E1>,
46{
47  move |input: I| match parser.parse((input, 0)) {
48    Ok(((rest, offset), result)) => {
49      // If the next byte has been partially read, it will be sliced away as well.
50      // The parser functions might already slice away all fully read bytes.
51      // That's why `offset / 8` isn't necessarily needed at all times.
52      let remaining_bytes_index = offset / 8 + if offset % 8 == 0 { 0 } else { 1 };
53      Ok((rest.slice(remaining_bytes_index..), result))
54    }
55    Err(Err::Incomplete(n)) => Err(Err::Incomplete(n.map(|u| u.get() / 8 + 1))),
56    Err(Err::Error(e)) => Err(Err::Error(e.convert())),
57    Err(Err::Failure(e)) => Err(Err::Failure(e.convert())),
58  }
59}
60
61/// Counterpart to `bits`, `bytes` transforms its bit stream input into a byte slice for the underlying
62/// parser, allowing byte-slice parsers to work on bit streams.
63///
64/// A partial byte remaining in the input will be ignored and the given parser will start parsing
65/// at the next full byte.
66///
67/// ```
68/// use nom::bits::{bits, bytes, streaming::take};
69/// use nom::combinator::rest;
70/// use nom::error::Error;
71/// use nom::sequence::tuple;
72/// use nom::IResult;
73///
74/// fn parse(input: &[u8]) -> IResult<&[u8], (u8, u8, &[u8])> {
75///   bits::<_, _, Error<(&[u8], usize)>, _, _>(tuple((
76///     take(4usize),
77///     take(8usize),
78///     bytes::<_, _, Error<&[u8]>, _, _>(rest)
79///   )))(input)
80/// }
81///
82/// let input = &[0x12, 0x34, 0xff, 0xff];
83///
84/// assert_eq!(parse( input ), Ok(( &[][..], (0x01, 0x23, &[0xff, 0xff][..]) )));
85/// ```
86pub fn bytes<I, O, E1, E2, P>(mut parser: P) -> impl FnMut((I, usize)) -> IResult<(I, usize), O, E2>
87where
88  E1: ParseError<I> + ErrorConvert<E2>,
89  E2: ParseError<(I, usize)>,
90  I: Slice<RangeFrom<usize>> + Clone,
91  P: Parser<I, O, E1>,
92{
93  move |(input, offset): (I, usize)| {
94    let inner = if offset % 8 != 0 {
95      input.slice((1 + offset / 8)..)
96    } else {
97      input.slice((offset / 8)..)
98    };
99    let i = (input, offset);
100    match parser.parse(inner) {
101      Ok((rest, res)) => Ok(((rest, 0), res)),
102      Err(Err::Incomplete(Needed::Unknown)) => Err(Err::Incomplete(Needed::Unknown)),
103      Err(Err::Incomplete(Needed::Size(sz))) => Err(match sz.get().checked_mul(8) {
104        Some(v) => Err::Incomplete(Needed::new(v)),
105        None => Err::Failure(E2::from_error_kind(i, ErrorKind::TooLarge)),
106      }),
107      Err(Err::Error(e)) => Err(Err::Error(e.convert())),
108      Err(Err::Failure(e)) => Err(Err::Failure(e.convert())),
109    }
110  }
111}
112
113#[cfg(test)]
114mod test {
115  use super::*;
116  use crate::bits::streaming::take;
117  use crate::error::Error;
118  use crate::sequence::tuple;
119
120  #[test]
121  /// Take the `bits` function and assert that remaining bytes are correctly returned, if the
122  /// previous bytes are fully consumed
123  fn test_complete_byte_consumption_bits() {
124    let input = &[0x12, 0x34, 0x56, 0x78];
125
126    // Take 3 bit slices with sizes [4, 8, 4].
127    let result: IResult<&[u8], (u8, u8, u8)> =
128      bits::<_, _, Error<(&[u8], usize)>, _, _>(tuple((take(4usize), take(8usize), take(4usize))))(
129        input,
130      );
131
132    let output = result.expect("We take 2 bytes and the input is longer than 2 bytes");
133
134    let remaining = output.0;
135    assert_eq!(remaining, [0x56, 0x78]);
136
137    let parsed = output.1;
138    assert_eq!(parsed.0, 0x01);
139    assert_eq!(parsed.1, 0x23);
140    assert_eq!(parsed.2, 0x04);
141  }
142
143  #[test]
144  /// Take the `bits` function and assert that remaining bytes are correctly returned, if the
145  /// previous bytes are NOT fully consumed. Partially consumed bytes are supposed to be dropped.
146  /// I.e. if we consume 1.5 bytes of 4 bytes, 2 bytes will be returned, bits 13-16 will be
147  /// dropped.
148  fn test_partial_byte_consumption_bits() {
149    let input = &[0x12, 0x34, 0x56, 0x78];
150
151    // Take bit slices with sizes [4, 8].
152    let result: IResult<&[u8], (u8, u8)> =
153      bits::<_, _, Error<(&[u8], usize)>, _, _>(tuple((take(4usize), take(8usize))))(input);
154
155    let output = result.expect("We take 1.5 bytes and the input is longer than 2 bytes");
156
157    let remaining = output.0;
158    assert_eq!(remaining, [0x56, 0x78]);
159
160    let parsed = output.1;
161    assert_eq!(parsed.0, 0x01);
162    assert_eq!(parsed.1, 0x23);
163  }
164
165  #[test]
166  #[cfg(feature = "std")]
167  /// Ensure that in Incomplete error is thrown, if too few bytes are passed for a given parser.
168  fn test_incomplete_bits() {
169    let input = &[0x12];
170
171    // Take bit slices with sizes [4, 8].
172    let result: IResult<&[u8], (u8, u8)> =
173      bits::<_, _, Error<(&[u8], usize)>, _, _>(tuple((take(4usize), take(8usize))))(input);
174
175    assert!(result.is_err());
176    let error = result.err().unwrap();
177    assert_eq!("Parsing requires 2 bytes/chars", error.to_string());
178  }
179}
nom/bits/mod.rs

nom/bits/
mod.rs
