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

use std::io::prelude::*;

struct VersionPrefix<W> {
    version: u8,
    has_seen_version: bool,
    wrapped: W,
}

impl<W> VersionPrefix<W> {
    fn new(version: char, wrapped: W) -> Self {
        VersionPrefix {
            version: version as u8,
            has_seen_version: false,
            wrapped,
        }
    }
}

pub struct VersionPrefixWriter<W>(VersionPrefix<W>);

impl<W> VersionPrefixWriter<W>
where
    W: Write,
{
    pub fn new(version: char, wrapped: W) -> VersionPrefixWriter<W> {
        VersionPrefixWriter(VersionPrefix::new(version, wrapped))
    }
}

impl<W> Write for VersionPrefixWriter<W>
where
    W: Write,
{
    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
        if self.0.has_seen_version {
            self.0.wrapped.write(buf)
        } else {
            self.0.has_seen_version = true;
            let mut new_buf = vec![0; buf.len() + 1];
            new_buf[0] = self.0.version;
            (&mut new_buf[1..]).copy_from_slice(buf);
            self.0.wrapped.write(&new_buf).map(|n| n - 1)
        }
    }

    fn flush(&mut self) -> std::io::Result<()> {
        self.0.wrapped.flush()
    }
}

pub struct VersionPrefixReader<R>(VersionPrefix<R>, Option<u8>);

impl<R> VersionPrefixReader<R>
where
    R: Read,
{
    pub fn new(version: char, wrapped: R) -> VersionPrefixReader<R> {
        VersionPrefixReader(VersionPrefix::new(version, wrapped), None)
    }

    /// return `None` when no bytes have been read, or the truth value
    /// of the statement "the first byte read matched the expected version".
    pub fn had_expected_version(&self) -> Option<bool> {
        self.1.map(|found| found == self.0.version)
    }
}

impl<R> Read for VersionPrefixReader<R>
where
    R: Read,
{
    fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
        if !self.0.has_seen_version {
            self.0.has_seen_version = true;
            let mut head_buf = vec![0];
            self.0.wrapped.read_exact(&mut head_buf)?;
            self.1 = Some(head_buf[0]);
        }
        self.0.wrapped.read(buf)
    }
}