1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130

use crate::fields::FixStr;
use nom::{
    bytes::streaming::tag,
    bytes::streaming::{take_until, take_while},
    character::{
        is_alphanumeric,
        streaming::{u16, u8},
    },
    combinator::{map, verify},
    error::{context, ContextError, ParseError},
    multi::length_data,
    sequence::{delimited, separated_pair, terminated, tuple},
    IResult,
};

pub use nom::Err;

// TODO: Don't use Nom, no need to use additional dependency for RawMessage processing.

pub fn generic_field<'a, E: ParseError<&'a [u8]> + ContextError<&'a [u8]>>(
    i: &'a [u8],
) -> IResult<&'a [u8], (u16, &[u8]), E> {
    terminated(
        separated_pair(u16, tag("="), take_until("\x01")),
        tag("\x01"),
    )(i)
}

fn verify_fix_str(bytes: &[u8]) -> bool {
    for b in bytes {
        // No control character is allowed
        if let 0x00..=0x1f | 0x80..=0xff = b {
            return false;
        }
    }
    true
}

fn begin_string<'a, E: ParseError<&'a [u8]> + ContextError<&'a [u8]>>(
    i: &'a [u8],
) -> IResult<&'a [u8], &[u8], E> {
    context(
        "begin_string",
        delimited(
            tag("8="),
            verify(take_until("\x01"), verify_fix_str),
            tag("\x01"),
        ),
    )(i)
}

fn checksum<'a, E: ParseError<&'a [u8]> + ContextError<&'a [u8]>>(
    i: &'a [u8],
) -> IResult<&[u8], u8, E> {
    context("checksum", delimited(tag("10="), u8, tag("\x01")))(i)
}

fn body_length<'a, E: ParseError<&'a [u8]> + ContextError<&'a [u8]>>(
    i: &'a [u8],
) -> IResult<&[u8], u16, E> {
    delimited(tag("9="), u16, tag("\x01"))(i)
}

fn _message_type<'a, E: ParseError<&'a [u8]> + ContextError<&'a [u8]>>(
    i: &'a [u8],
) -> IResult<&[u8], &[u8], E> {
    context(
        "message_type",
        delimited(tag("35="), take_while(is_alphanumeric), tag("\x01")),
    )(i)
}

#[derive(Debug)]
pub struct RawMessage<'a> {
    pub begin_string: &'a FixStr,
    pub body: &'a [u8],
    pub checksum: u8,
}

pub fn raw_message<'a>(i: &'a [u8]) -> IResult<&'a [u8], RawMessage<'a>> {
    map(
        tuple((begin_string, length_data(body_length), checksum)),
        |(begin_string, body, checksum)| RawMessage {
            // SAFETY: it's already checked
            begin_string: unsafe { FixStr::from_ascii_unchecked(begin_string) },
            body,
            checksum,
        },
    )(i)
}

#[cfg(test)]
mod tests {
    use super::raw_message;
    use nom::Err::Incomplete;

    #[test]
    fn parse_complete_ok() {
        let input = b"8=MSG_BODY\x019=19\x01<lots of tags here>10=015\x01";
        assert!(raw_message(input).is_ok());
    }

    #[test]
    fn parse_from_chunks_ok() {
        let input = &[
            b"8=MSG_BOD".as_slice(),
            b"Y\x019=19\x01<lots".as_slice(),
            b" of tags here>10=015\x01".as_slice(),
            b"leftover".as_slice(),
        ];
        let mut buf = Vec::new();
        let mut i = input.iter();
        {
            buf.extend_from_slice(i.next().unwrap());
            assert!(matches!(raw_message(&buf), Err(Incomplete(_))));
        }
        {
            buf.extend_from_slice(i.next().unwrap());
            assert!(matches!(raw_message(&buf), Err(Incomplete(_))));
        }
        {
            buf.extend_from_slice(i.next().unwrap());
            assert!(matches!(raw_message(&buf), Ok(([], _))));
        }
        {
            buf.extend_from_slice(i.next().unwrap());
            assert!(matches!(raw_message(&buf), Ok((b"leftover", _))));
        }
    }
}