mail-parser 1.0.0

Fast and robust e-mail parsing library for Rust
Documentation 
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
131
132
133
134
135
136
137
138
139
140
141
142
143

/*
 * SPDX-FileCopyrightText: 2020 Stalwart Labs LLC <hello@stalw.art>
 *
 * SPDX-License-Identifier: Apache-2.0 OR MIT
 */

#[cfg(feature = "full_encoding")]
use encoding_rs::{Encoding, UTF_16BE, UTF_16LE};

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub(super) enum Endian {
    Little,
    Big,
}

const UNIT: usize = 2;
const LEAD_SURROGATES: std::ops::RangeInclusive<u16> = 0xd800..=0xdbff;

pub(super) fn complete_prefix_bom(bytes: &[u8]) -> &[u8] {
    match bytes {
        [0xfe, 0xff, rest @ ..] => bytes
            .get(..UNIT + Endian::Big.complete_prefix(rest).len())
            .unwrap_or_default(),
        [0xff, 0xfe, rest @ ..] => bytes
            .get(..UNIT + Endian::Little.complete_prefix(rest).len())
            .unwrap_or_default(),
        [_, _, ..] => Endian::Little.complete_prefix(bytes),
        _ => &[],
    }
}

pub(super) fn decode_bom(bytes: &[u8]) -> String {
    let mut out = String::new();
    decode_bom_append(bytes, &mut out);
    out
}

pub(super) fn decode_bom_append(bytes: &[u8], out: &mut String) {
    match bytes {
        [0xfe, 0xff, rest @ ..] => Endian::Big.decode_append(rest, out),
        [0xff, 0xfe, rest @ ..] => Endian::Little.decode_append(rest, out),
        _ => Endian::Little.decode_append(bytes, out),
    }
}

pub(super) fn decode_bom_checked(bytes: &[u8]) -> (String, bool) {
    match bytes {
        [0xfe, 0xff, rest @ ..] => Endian::Big.decode_checked(rest),
        [0xff, 0xfe, rest @ ..] => Endian::Little.decode_checked(rest),
        _ => Endian::Little.decode_checked(bytes),
    }
}

impl Endian {
    fn unit(self, bytes: [u8; UNIT]) -> u16 {
        match self {
            Endian::Little => u16::from_le_bytes(bytes),
            Endian::Big => u16::from_be_bytes(bytes),
        }
    }

    pub(super) fn complete_prefix(self, bytes: &[u8]) -> &[u8] {
        let units = bytes.as_chunks::<UNIT>().0;
        let complete = match units.last() {
            Some(&unit) if LEAD_SURROGATES.contains(&self.unit(unit)) => units.len() - 1,
            _ => units.len(),
        };
        bytes.get(..complete * UNIT).unwrap_or_default()
    }

    pub(super) fn decode(self, bytes: &[u8]) -> String {
        let mut out = String::new();
        self.decode_append(bytes, &mut out);
        out
    }

    #[cfg(feature = "full_encoding")]
    pub(super) fn decode_checked(self, bytes: &[u8]) -> (String, bool) {
        let (text, replaced) = self.encoding().decode_without_bom_handling(bytes);
        (text.into_owned(), replaced)
    }

    #[cfg(not(feature = "full_encoding"))]
    pub(super) fn decode_checked(self, bytes: &[u8]) -> (String, bool) {
        use std::char::{REPLACEMENT_CHARACTER, decode_utf16};

        let (units, odd) = bytes.as_chunks::<UNIT>();
        let mut malformed = !odd.is_empty();
        let mut out = String::with_capacity(units.len());
        out.extend(
            decode_utf16(units.iter().map(|&unit| self.unit(unit))).map(|result| {
                result.unwrap_or_else(|_| {
                    malformed = true;
                    REPLACEMENT_CHARACTER
                })
            }),
        );
        if self.replaces_odd_byte(units, odd) {
            out.push(REPLACEMENT_CHARACTER);
        }
        (out, malformed)
    }

    #[cfg(not(feature = "full_encoding"))]
    fn replaces_odd_byte(self, units: &[[u8; UNIT]], odd: &[u8]) -> bool {
        !odd.is_empty()
            && !units
                .last()
                .is_some_and(|&unit| LEAD_SURROGATES.contains(&self.unit(unit)))
    }

    #[cfg(feature = "full_encoding")]
    pub(super) fn decode_append(self, bytes: &[u8], out: &mut String) {
        super::multi_byte::decode_with(
            self.encoding().new_decoder_without_bom_handling(),
            bytes,
            out,
        );
    }

    #[cfg(feature = "full_encoding")]
    fn encoding(self) -> &'static Encoding {
        match self {
            Endian::Little => UTF_16LE,
            Endian::Big => UTF_16BE,
        }
    }

    #[cfg(not(feature = "full_encoding"))]
    pub(super) fn decode_append(self, bytes: &[u8], out: &mut String) {
        use std::char::{REPLACEMENT_CHARACTER, decode_utf16};

        let (units, odd) = bytes.as_chunks::<UNIT>();
        out.reserve(units.len());
        out.extend(
            decode_utf16(units.iter().map(|&unit| self.unit(unit)))
                .map(|result| result.unwrap_or(REPLACEMENT_CHARACTER)),
        );
        if self.replaces_odd_byte(units, odd) {
            out.push(REPLACEMENT_CHARACTER);
        }
    }
}