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

use alloc::vec::Vec;

use crate::Decoder;
use crate::error::UnexpectedEnd;

#[derive(Debug)]
pub struct ByteVecDecoder {
    buf: Vec<u8>,
    required: usize,
}

impl ByteVecDecoder {
    pub fn new(required_bytes: usize) -> Self {
        ByteVecDecoder {
            buf: Vec::with_capacity(required_bytes),
            required: required_bytes,
        }
    }
}

impl Decoder for ByteVecDecoder {
    type Value = Vec<u8>;
    type Error = UnexpectedEnd;

    fn decode_chunk(&mut self, bytes: &mut &[u8]) -> Result<(), Self::Error> {
        let to_copy = bytes.len().min(self.required - self.buf.len());
        self.buf.extend_from_slice(&bytes[..to_copy]);
        *bytes = &bytes[to_copy..];
        Ok(())
    }

    fn end(self) -> Result<Self::Value, Self::Error> {
        if self.buf.len() < self.required {
            Err(UnexpectedEnd { missing: self.required - self.buf.len() })
        } else {
            Ok(self.buf)
        }
    }
}

#[cfg(test)]
mod tests {
    use super::ByteVecDecoder;
    use crate::Decoder;

    #[test]
    fn empty() {
        let mut decoder = ByteVecDecoder::new(0);
        assert_eq!(decoder.bytes_received(&[42]).unwrap(), 0);
        decoder.end().unwrap();
    }

    #[test]
    fn empty_immediate_end() {
        let decoder = ByteVecDecoder::new(0);
        decoder.end().unwrap();
    }

    #[test]
    fn one() {
        let mut decoder = ByteVecDecoder::new(1);
        assert_eq!(decoder.bytes_received(&[42, 21]).unwrap(), 1);
        assert_eq!(decoder.end().unwrap(), [42]);
    }

    #[test]
    fn one_immediate_end() {
        let mut decoder = ByteVecDecoder::new(1);
        assert_eq!(decoder.bytes_received(&[42]).unwrap(), 1);
        assert_eq!(decoder.end().unwrap(), [42]);
    }

    #[test]
    fn two_single() {
        let mut decoder = ByteVecDecoder::new(2);
        assert_eq!(decoder.bytes_received(&[42, 21]).unwrap(), 2);
        assert_eq!(decoder.end().unwrap(), [42, 21]);
    }

    #[test]
    fn two_split() {
        let mut decoder = ByteVecDecoder::new(2);
        assert_eq!(decoder.bytes_received(&[42]).unwrap(), 1);
        assert_eq!(decoder.bytes_received(&[21]).unwrap(), 1);
        assert_eq!(decoder.end().unwrap(), [42, 21]);
    }

    #[test]
    fn two_split_extra() {
        let mut decoder = ByteVecDecoder::new(2);
        assert_eq!(decoder.bytes_received(&[42]).unwrap(), 1);
        assert_eq!(decoder.bytes_received(&[21, 47]).unwrap(), 1);
        assert_eq!(decoder.end().unwrap(), [42, 21]);
    }
}