rust - 一个关于用 Rust 中的 crate Nom 解析 http 头的奇怪问题

Question

我编写了一些使用 NOM 解析 HTTP header 的代码，但得到了一些奇怪的结果，如示例所示。
在 main 函数中，字符串 input1 的末尾只比 input2 多了一个分号，但得到的结果却完全不同。显然，我希望得到与 text(input2) 类似的结果，感谢您帮助我检查发生了什么。

[dependencies]
nom = "6"

use nom::{
    branch::alt,
    bytes::complete::{tag, tag_no_case, take_until},
    character::complete::multispace0,
    combinator::opt,
    multi::separated_list0,
    sequence::tuple,
};
use nom::{AsChar, IResult, InputTakeAtPosition};
use std::collections::HashMap;
use std::fmt::Debug;

#[derive(Debug, PartialEq)]
pub struct Header<'a> {
    pub options_header_cookies: HashMap<&'a str, &'a str>,
    pub options_headers_more: HashMap<&'a str, &'a str>,
}

#[allow(dead_code)]
fn key(input: &str) -> IResult<&str, &str> {
    input.split_at_position_complete(|item| {
        !(item.is_alphanum() || item.as_char() == '-' || item.as_char() == '_')
    })
}

#[allow(dead_code)]
fn cookie_pairs(input: &str) -> IResult<&str, HashMap<&str, &str>> {
    let (input, cookies) = separated_list0(
        tag(";"),
        tuple((
            multispace0,
            key,
            tag("="),
            alt((take_until(";"), take_until("'"))),
            multispace0,
        )),
    )(input)?;
    Ok((input, cookies.into_iter().map(|c| (c.1, c.3)).collect()))
}

#[allow(dead_code)]
fn options_header_cookie(input: &str) -> IResult<&str, HashMap<&str, &str>> {
    let (input, (_, _, cookies, _)) = tuple((
        alt((tag("-H\x20"), tag("--header\x20"))),
        tag_no_case("'cookie:\x20"),
        cookie_pairs,
        tag("'"),
    ))(input)?;
    Ok((input, cookies))
}

#[allow(dead_code)]
fn options_header_(input: &str) -> IResult<&str, (&str, &str)> {
    let (input, (_, k, _, v, _)) = tuple((
        alt((tag("-H\x20'"), tag("--header\x20'"))),
        key,
        tag(":\x20"),
        take_until("'"),
        tag("'"),
    ))(input)?;
    Ok((input, (k, v)))
}

fn text(input: &str) -> IResult<&str, Header> {
    let mut h = Header {
        options_header_cookies: HashMap::new(),
        options_headers_more: HashMap::new(),
    };
    let (input, opts) = separated_list0(
        tag("\x20"),
        tuple((
            opt(tag("\\\n")),
            multispace0,
            tuple((opt(options_header_cookie), opt(options_header_))),
        )),
    )(input)?;
    for (_, _, o) in opts {
        if let Some(cookies) = o.0 {
            h.options_header_cookies = cookies;
            continue;
        }else if let Some(header) = o.1 {
            h.options_headers_more.insert(header.0, header.1);
            continue;
        }
    }
    Ok((input, h))
}

#[allow(dead_code)]
fn debug<T: Debug>(o: T) {
    println!("=> {:#?}", o);
}

fn main() {
    let input1 = r#"
-H 'Cookie: NID=219=Ji47zdfV6mSKlkKmpVf8F67O80WTSw; DV=03-vBWQ2RBEqsNFUD5FEuieRJvkwrRfXaKa0v0Cj2wAAAAA' \
-H 'User-Agent: Mozilla/5.0 Macintosh;'"#;

    debug(text(input1));

    let input2 = r#"
-H 'Cookie: NID=219=Ji47zdfV6mSKlkKmpVf8F67O80WTSw; DV=03-vBWQ2RBEqsNFUD5FEuieRJvkwrRfXaKa0v0Cj2wAAAAA' \
-H 'User-Agent: Mozilla/5.0 Macintosh'"#;

    debug(text(input2));
}

Answer 1

问题出在您的 cookie_pairs()解析器:

fn cookie_pairs(input: &str) -> IResult<&str, HashMap<&str, &str>> {
    let (input, cookies) = separated_list0(
        tag(";"),
        tuple((
            multispace0,
            key,
            tag("="),
            alt((take_until(";"), take_until("'"))),
            multispace0,
        )),
    )(input)?;
    Ok((input, cookies.into_iter().map(|c| (c.1, c.3)).collect()))
}

alt()组合器运行第一个解析器直到完成，只有当它失败时，才会尝试第二个:

alt((take_until(";"), take_until("'")))

所以在尾随 ; 的情况下该解析器本质上消耗了整个输入，从而使父解析器失败并且不返回任何 cookie。
修复很简单。您必须将其替换为:

take_while(|ch| ch != '\'' && ch != ';')

这将在 ' 时停止或 ;出现并且不会消耗整个输入:

fn cookie_pairs(input: &str) -> IResult<&str, HashMap<&str, &str>> {
    let (input, cookies) = separated_list0(
        tag(";"),
        tuple((
            multispace0,
            key,
            tag("="),
            take_while(|ch| ch != '\'' && ch != ';'),
            multispace0,
        )),
    )(input)?;
    Ok((input, cookies.into_iter().map(|c| (c.1, c.3)).collect()))
}