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

use crate::io::{AsyncBufRead, AsyncRead, ReadBuf};

use pin_project_lite::pin_project;
use std::fmt;
use std::io;
use std::pin::Pin;
use std::task::{Context, Poll};

pin_project! {
    /// Stream for the [`chain`](super::AsyncReadExt::chain) method.
    #[must_use = "streams do nothing unless polled"]
    #[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
    pub struct Chain<T, U> {
        #[pin]
        first: T,
        #[pin]
        second: U,
        done_first: bool,
    }
}

pub(super) fn chain<T, U>(first: T, second: U) -> Chain<T, U>
where
    T: AsyncRead,
    U: AsyncRead,
{
    Chain {
        first,
        second,
        done_first: false,
    }
}

impl<T, U> Chain<T, U>
where
    T: AsyncRead,
    U: AsyncRead,
{
    /// Gets references to the underlying readers in this `Chain`.
    pub fn get_ref(&self) -> (&T, &U) {
        (&self.first, &self.second)
    }

    /// Gets mutable references to the underlying readers in this `Chain`.
    ///
    /// Care should be taken to avoid modifying the internal I/O state of the
    /// underlying readers as doing so may corrupt the internal state of this
    /// `Chain`.
    pub fn get_mut(&mut self) -> (&mut T, &mut U) {
        (&mut self.first, &mut self.second)
    }

    /// Gets pinned mutable references to the underlying readers in this `Chain`.
    ///
    /// Care should be taken to avoid modifying the internal I/O state of the
    /// underlying readers as doing so may corrupt the internal state of this
    /// `Chain`.
    pub fn get_pin_mut(self: Pin<&mut Self>) -> (Pin<&mut T>, Pin<&mut U>) {
        let me = self.project();
        (me.first, me.second)
    }

    /// Consumes the `Chain`, returning the wrapped readers.
    pub fn into_inner(self) -> (T, U) {
        (self.first, self.second)
    }
}

impl<T, U> fmt::Debug for Chain<T, U>
where
    T: fmt::Debug,
    U: fmt::Debug,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Chain")
            .field("t", &self.first)
            .field("u", &self.second)
            .finish()
    }
}

impl<T, U> AsyncRead for Chain<T, U>
where
    T: AsyncRead,
    U: AsyncRead,
{
    fn poll_read(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &mut ReadBuf<'_>,
    ) -> Poll<io::Result<()>> {
        let me = self.project();

        if !*me.done_first {
            let rem = buf.remaining();
            ready!(me.first.poll_read(cx, buf))?;
            if buf.remaining() == rem {
                *me.done_first = true;
            } else {
                return Poll::Ready(Ok(()));
            }
        }
        me.second.poll_read(cx, buf)
    }
}

impl<T, U> AsyncBufRead for Chain<T, U>
where
    T: AsyncBufRead,
    U: AsyncBufRead,
{
    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
        let me = self.project();

        if !*me.done_first {
            match ready!(me.first.poll_fill_buf(cx)?) {
                [] => {
                    *me.done_first = true;
                }
                buf => return Poll::Ready(Ok(buf)),
            }
        }
        me.second.poll_fill_buf(cx)
    }

    fn consume(self: Pin<&mut Self>, amt: usize) {
        let me = self.project();
        if !*me.done_first {
            me.first.consume(amt)
        } else {
            me.second.consume(amt)
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn assert_unpin() {
        crate::is_unpin::<Chain<(), ()>>();
    }
}