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

nom/bits/
mod.rs
