lossy.rs.html -- source
Description: Source to the Rust file `library/core/src/str/lossy.rs`.
Keywords: rust, rustlang, rust-lang

      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
    144
    145
    146
    147
    148
    149
    150
    151
    152
    153
    154
    155
    156
    157
    158
    159
    160
    161
    162
    163
    164
    165
    166
    167
    168
    169
    170
    171
    172
    173
    174
    175
    176
    177
    178
    179
    180
    181
    182
    183
    184
    185
    186
    187
    188
    189
    190
    191
    192
    193
    194
    195
    196
    197
    198
    199
    200
    201
    202
    203

    use crate::char;
    use crate::fmt::{self, Write};
    use crate::mem;

    use super::from_utf8_unchecked;
    use super::validations::utf8_char_width;

    /// Lossy UTF-8 string.
    #[unstable(feature = "str_internals", issue = "none")]
    pub struct Utf8Lossy {
        bytes: [u8],
    }

    impl Utf8Lossy {
        pub fn from_str(s: &str) -> &Utf8Lossy {
            Utf8Lossy::from_bytes(s.as_bytes())
        }

        pub fn from_bytes(bytes: &[u8]) -> &Utf8Lossy {
            // SAFETY: Both use the same memory layout, and UTF-8 correctness isn't required.
            unsafe { mem::transmute(bytes) }
        }

        pub fn chunks(&self) -> Utf8LossyChunksIter<'_> {
            Utf8LossyChunksIter { source: &self.bytes }
        }
    }

    /// Iterator over lossy UTF-8 string
    #[unstable(feature = "str_internals", issue = "none")]
    #[allow(missing_debug_implementations)]
    pub struct Utf8LossyChunksIter<'a> {
        source: &'a [u8],
    }

    #[unstable(feature = "str_internals", issue = "none")]
    #[derive(PartialEq, Eq, Debug)]
    pub struct Utf8LossyChunk<'a> {
        /// Sequence of valid chars.
        /// Can be empty between broken UTF-8 chars.
        pub valid: &'a str,
        /// Single broken char, empty if none.
        /// Empty iff iterator item is last.
        pub broken: &'a [u8],
    }

    impl<'a> Iterator for Utf8LossyChunksIter<'a> {
        type Item = Utf8LossyChunk<'a>;

        fn next(&mut self) -> Option<Utf8LossyChunk<'a>> {
            if self.source.is_empty() {
                return None;
            }

            const TAG_CONT_U8: u8 = 128;
            fn safe_get(xs: &[u8], i: usize) -> u8 {
                *xs.get(i).unwrap_or(&0)
            }

            let mut i = 0;
            while i < self.source.len() {
                let i_ = i;

                // SAFETY: `i` starts at `0`, is less than `self.source.len()`, and
                // only increases, so `0 <= i < self.source.len()`.
                let byte = unsafe { *self.source.get_unchecked(i) };
                i += 1;

                if byte < 128 {
                } else {
                    let w = utf8_char_width(byte);

                    macro_rules! error {
                        () => {{
                            // SAFETY: We have checked up to `i` that source is valid UTF-8.
                            unsafe {
                                let r = Utf8LossyChunk {
                                    valid: from_utf8_unchecked(&self.source[0..i_]),
                                    broken: &self.source[i_..i],
                                };
                                self.source = &self.source[i..];
                                return Some(r);
                            }
                        }};
                    }

                    match w {
                        2 => {
                            if safe_get(self.source, i) & 192 != TAG_CONT_U8 {
                                error!();
                            }
                            i += 1;
                        }
                        3 => {
                            match (byte, safe_get(self.source, i)) {
                                (0xE0, 0xA0..=0xBF) => (),
                                (0xE1..=0xEC, 0x80..=0xBF) => (),
                                (0xED, 0x80..=0x9F) => (),
                                (0xEE..=0xEF, 0x80..=0xBF) => (),
                                _ => {
                                    error!();
                                }
                            }
                            i += 1;
                            if safe_get(self.source, i) & 192 != TAG_CONT_U8 {
                                error!();
                            }
                            i += 1;
                        }
                        4 => {
                            match (byte, safe_get(self.source, i)) {
                                (0xF0, 0x90..=0xBF) => (),
                                (0xF1..=0xF3, 0x80..=0xBF) => (),
                                (0xF4, 0x80..=0x8F) => (),
                                _ => {
                                    error!();
                                }
                            }
                            i += 1;
                            if safe_get(self.source, i) & 192 != TAG_CONT_U8 {
                                error!();
                            }
                            i += 1;
                            if safe_get(self.source, i) & 192 != TAG_CONT_U8 {
                                error!();
                            }
                            i += 1;
                        }
                        _ => {
                            error!();
                        }
                    }
                }
            }

            let r = Utf8LossyChunk {
                // SAFETY: We have checked that the entire source is valid UTF-8.
                valid: unsafe { from_utf8_unchecked(self.source) },
                broken: &[],
            };
            self.source = &[];
            Some(r)
        }
    }

    impl fmt::Display for Utf8Lossy {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            // If we're the empty string then our iterator won't actually yield
            // anything, so perform the formatting manually
            if self.bytes.is_empty() {
                return "".fmt(f);
            }

            for Utf8LossyChunk { valid, broken } in self.chunks() {
                // If we successfully decoded the whole chunk as a valid string then
                // we can return a direct formatting of the string which will also
                // respect various formatting flags if possible.
                if valid.len() == self.bytes.len() {
                    assert!(broken.is_empty());
                    return valid.fmt(f);
                }

                f.write_str(valid)?;
                if !broken.is_empty() {
                    f.write_char(char::REPLACEMENT_CHARACTER)?;
                }
            }
            Ok(())
        }
    }

    impl fmt::Debug for Utf8Lossy {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.write_char('"')?;

            for Utf8LossyChunk { valid, broken } in self.chunks() {
                // Valid part.
                // Here we partially parse UTF-8 again which is suboptimal.
                {
                    let mut from = 0;
                    for (i, c) in valid.char_indices() {
                        let esc = c.escape_debug();
                        // If char needs escaping, flush backlog so far and write, else skip
                        if esc.len() != 1 {
                            f.write_str(&valid[from..i])?;
                            for c in esc {
                                f.write_char(c)?;
                            }
                            from = i + c.len_utf8();
                        }
                    }
                    f.write_str(&valid[from..])?;
                }

                // Broken parts of string as hex escape.
                for &b in broken {
                    write!(f, "\\x{:02x}", b)?;
                }
            }

            f.write_char('"')
        }
    }