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

#[macro_use] extern crate matches;

mod polyfill;
mod lossy;

pub use lossy::LossyDecoder;

use std::cmp;
use std::str;

/// The replacement character, U+FFFD. In lossy decoding, insert it for every decoding error.
pub const REPLACEMENT_CHARACTER: &'static str = "\u{FFFD}";

#[derive(Debug, Copy, Clone)]
pub enum DecodeError<'a> {
    /// In lossy decoding insert `valid_prefix`, then `"\u{FFFD}"`,
    /// then call `decode()` again with `remaining_input`.
    Invalid {
        valid_prefix: &'a str,
        invalid_sequence: &'a [u8],
        remaining_input: &'a [u8],
    },

    /// Call the `incomplete_suffix.try_complete` method with more input when available.
    /// If no more input is available, this is an invalid byte sequence.
    Incomplete {
        valid_prefix: &'a str,
        incomplete_suffix: Incomplete,
    },
}

#[derive(Debug, Copy, Clone)]
pub struct Incomplete {
    pub buffer: [u8; 4],
    pub buffer_len: u8,
}

pub fn decode(input: &[u8]) -> Result<&str, DecodeError> {
    let error = match str::from_utf8(input) {
        Ok(valid) => return Ok(valid),
        Err(error) => error,
    };

    // FIXME: separate function from here to guide inlining?
    let (valid, after_valid) = input.split_at(error.valid_up_to());
    let valid = unsafe {
        str::from_utf8_unchecked(valid)
    };

    match polyfill::utf8error_error_len(&error, input) {
        Some(invalid_sequence_length) => {
            let (invalid, rest) = after_valid.split_at(invalid_sequence_length);
            Err(DecodeError::Invalid {
                valid_prefix: valid,
                invalid_sequence: invalid,
                remaining_input: rest
            })
        }
        None => {
            Err(DecodeError::Incomplete {
                valid_prefix: valid,
                incomplete_suffix: Incomplete::new(after_valid),
            })
        }
    }
}

impl Incomplete {
    pub fn empty() -> Self {
        Incomplete {
            buffer: [0, 0, 0, 0],
            buffer_len: 0,
        }
    }

    pub fn is_empty(&self) -> bool {
        self.buffer_len == 0
    }

    pub fn new(bytes: &[u8]) -> Self {
        let mut buffer = [0, 0, 0, 0];
        let len = bytes.len();
        buffer[..len].copy_from_slice(bytes);
        Incomplete {
            buffer: buffer,
            buffer_len: len as u8,
        }
    }

    /// * `None`: still incomplete, call `try_complete` again with more input.
    ///   If no more input is available, this is invalid byte sequence.
    /// * `Some((result, remaining_input))`: We’re done with this `Incomplete`.
    ///   To keep decoding, pass `remaining_input` to `decode()`.
    pub fn try_complete<'input>(&mut self, input: &'input [u8])
                                -> Option<(Result<&str, &[u8]>, &'input [u8])> {
        let buffer_len = self.buffer_len as usize;
        let copied_from_input;
        {
            let unwritten = &mut self.buffer[buffer_len..];
            copied_from_input = cmp::min(unwritten.len(), input.len());
            unwritten[..copied_from_input].copy_from_slice(&input[..copied_from_input]);
        }
        let spliced = &self.buffer[..buffer_len + copied_from_input];
        match str::from_utf8(spliced) {
            Ok(valid) => {
                self.buffer_len = 0;
                Some((Ok(valid), &input[copied_from_input..]))
            }
            Err(error) => {
                let valid_up_to = error.valid_up_to();
                if valid_up_to > 0 {
                    let valid = &self.buffer[..valid_up_to];
                    let valid = unsafe {
                        str::from_utf8_unchecked(valid)
                    };
                    let consumed = valid_up_to.checked_sub(buffer_len).unwrap();
                    self.buffer_len = 0;
                    Some((Ok(valid), &input[consumed..]))
                } else {
                    match polyfill::utf8error_error_len(&error, spliced) {
                        Some(invalid_sequence_length) => {
                            let invalid = &spliced[..invalid_sequence_length];
                            let consumed = invalid_sequence_length.checked_sub(buffer_len).unwrap();
                            let rest = &input[consumed..];
                            self.buffer_len = 0;
                            Some((Err(invalid), rest))
                        }
                        None => {
                            self.buffer_len = spliced.len() as u8;
                            None
                        }
                    }
                }
            }
        }
    }
}