tartan_parsers/
lib.rs

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//! Utilities for nom parsers

#![no_std]
#![warn(missing_docs)]
#![warn(clippy::pedantic)]
#![allow(clippy::must_use_candidate)]
#![allow(clippy::upper_case_acronyms)]

use nom::combinator::cut;
use nom::error::{ContextError, ParseError};
use nom::sequence::preceded;
use nom::{IResult, InputLength, Parser};


/// Helpers for reporting parsing errors
pub mod error;


/// Parse struct fields in order using an initializer-like syntax
///
/// # Example
///
/// ```
/// # use nom::IResult;
/// # use nom::character::complete::alphanumeric1;
/// # use nom::number::complete::le_u16;
/// # use tartan_parsers::struct_parser;
/// #
/// type Parser<'a, T> = fn(&'a [u8]) -> IResult<&'a [u8], T, ()>;
///
/// # #[derive(Debug, Clone, Copy, PartialEq, Eq)]
/// struct Foo<'a> { a: u16, b: &'a [u8] };
///
/// // Will parse `a`, then `b`, and return the struct if both succeed
/// let parse_foo: Parser<Foo> = struct_parser!(
///     Foo {
///         a: le_u16,
///         b: alphanumeric1,
///     }
/// );
///
/// assert_eq!(
///     parse_foo(b"\x34\x12Bar10"),
///     Ok((b"" as &[u8], Foo { a: 0x1234, b: b"Bar10" }))
/// );
/// ```
#[macro_export]
macro_rules! struct_parser {
    // Struct form
    [
        $struct:ident $( :: $struct_x:ident )* {
            $( $field:ident : $parser:expr ),+
            $(,)?
        }
    ] => {
        |i| {
            $( let (i, $field) = $parser(i)?; )+
            let result = ($struct $(::$struct_x)* { $($field),+ });
            Ok((i, result))
        }
    };

    // Tuple form
    [
        $struct:ident $( :: $struct_x:ident )* (
            $( $parser:expr ),+
            $(,)?
        )
    ] => {
        |i| {
            let (i, t) = nom::sequence::tuple(( $($parser),+ ))(i)?;
            let result = Fn::call(& $struct $(::$struct_x)*, t);
            Ok((i, result))
        }
    };
}


/// Combinator for productions that use a deterministic opcode
///
/// If a production is preceded by an unambiguous opcode, then we can avoid
/// backtracking when parsing the rest. This enables better error messages in addition
/// to faster parsing.
pub fn opcode<I, O1, O2, E, P, Q>(
    description: &'static str,
    opcode_parser: P,
    body_parser: Q,
) -> impl FnMut(I) -> IResult<I, O2, E>
where
    I: Clone,
    P: Parser<I, O1, E>,
    Q: Parser<I, O2, E>,
    E: ParseError<I> + ContextError<I>,
{
    let mut parser = preceded(opcode_parser, cut(body_parser));
    move |i: I| match parser.parse(i.clone()) {
        Err(nom::Err::Failure(e)) => {
            // Only add context to *failures*, on the assumption that these will only
            // come from the opcode body, and we don't want to add context when the
            // opcode itself wasn't recognized.
            Err(nom::Err::Failure(E::add_context(i, description, e)))
        }
        other => other,
    }
}


/// Create an iterator that repeatedly executes the parser.
///
/// Unlike [`nom::combinator::iterator`], this yields a [`Result`] at every step, so
/// errors are returned in the stream, and there is no separate `finish()` method. If the
/// parser encounters an error, the iterator will yield that error and not attempt to
/// parse any more elements.
pub fn result_iterator<P, I, O, E>(
    input: I,
    parser: P,
) -> impl Iterator<Item = Result<O, nom::Err<E>>>
where
    P: Fn(I) -> IResult<I, O, E>,
    I: InputLength,
    E: ParseError<I>,
{
    ResultIterator { input: Some(input), parser }
}


struct ResultIterator<P, I, O, E>
where
    P: Fn(I) -> IResult<I, O, E>,
    I: InputLength,
    E: ParseError<I>,
{
    input: Option<I>,
    parser: P,
}

impl<P, I, O, E> Iterator for ResultIterator<P, I, O, E>
where
    P: Fn(I) -> IResult<I, O, E>,
    I: InputLength,
    E: ParseError<I>,
{
    type Item = Result<O, nom::Err<E>>;

    fn next(&mut self) -> Option<Self::Item> {
        let mut input = None;
        core::mem::swap(&mut self.input, &mut input);
        match input {
            None => None,
            Some(i) if i.input_len() == 0 => None,
            Some(i) => match (self.parser)(i) {
                Ok((rest, output)) => {
                    self.input = Some(rest);
                    Some(Ok(output))
                }
                Err(e) => {
                    self.input = None;
                    Some(Err(e))
                }
            },
        }
    }
}