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
204
205
206
207
use crate::io::util::{BufReader, BufWriter};
use crate::io::{AsyncBufRead, AsyncRead, AsyncSeek, AsyncWrite, ReadBuf};

use pin_project_lite::pin_project;
use std::io::{self, IoSlice, SeekFrom};
use std::pin::Pin;
use std::task::{Context, Poll};

pin_project! {
    /// Wraps a type that is [`AsyncWrite`] and [`AsyncRead`], and buffers its input and output.
    ///
    /// It can be excessively inefficient to work directly with something that implements [`AsyncWrite`]
    /// and [`AsyncRead`]. For example, every `write`, however small, has to traverse the syscall
    /// interface, and similarly, every read has to do the same. The [`BufWriter`] and [`BufReader`]
    /// types aid with these problems respectively, but do so in only one direction. `BufStream` wraps
    /// one in the other so that both directions are buffered. See their documentation for details.
    #[derive(Debug)]
    #[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
    pub struct BufStream<RW> {
        #[pin]
        inner: BufReader<BufWriter<RW>>,
    }
}

impl<RW: AsyncRead + AsyncWrite> BufStream<RW> {
    /// Wraps a type in both [`BufWriter`] and [`BufReader`].
    ///
    /// See the documentation for those types and [`BufStream`] for details.
    pub fn new(stream: RW) -> BufStream<RW> {
        BufStream {
            inner: BufReader::new(BufWriter::new(stream)),
        }
    }

    /// Creates a `BufStream` with the specified [`BufReader`] capacity and [`BufWriter`]
    /// capacity.
    ///
    /// See the documentation for those types and [`BufStream`] for details.
    pub fn with_capacity(
        reader_capacity: usize,
        writer_capacity: usize,
        stream: RW,
    ) -> BufStream<RW> {
        BufStream {
            inner: BufReader::with_capacity(
                reader_capacity,
                BufWriter::with_capacity(writer_capacity, stream),
            ),
        }
    }

    /// Gets a reference to the underlying I/O object.
    ///
    /// It is inadvisable to directly read from the underlying I/O object.
    pub fn get_ref(&self) -> &RW {
        self.inner.get_ref().get_ref()
    }

    /// Gets a mutable reference to the underlying I/O object.
    ///
    /// It is inadvisable to directly read from the underlying I/O object.
    pub fn get_mut(&mut self) -> &mut RW {
        self.inner.get_mut().get_mut()
    }

    /// Gets a pinned mutable reference to the underlying I/O object.
    ///
    /// It is inadvisable to directly read from the underlying I/O object.
    pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut RW> {
        self.project().inner.get_pin_mut().get_pin_mut()
    }

    /// Consumes this `BufStream`, returning the underlying I/O object.
    ///
    /// Note that any leftover data in the internal buffer is lost.
    pub fn into_inner(self) -> RW {
        self.inner.into_inner().into_inner()
    }
}

impl<RW> From<BufReader<BufWriter<RW>>> for BufStream<RW> {
    fn from(b: BufReader<BufWriter<RW>>) -> Self {
        BufStream { inner: b }
    }
}

impl<RW> From<BufWriter<BufReader<RW>>> for BufStream<RW> {
    fn from(b: BufWriter<BufReader<RW>>) -> Self {
        // we need to "invert" the reader and writer
        let BufWriter {
            inner:
                BufReader {
                    inner,
                    buf: rbuf,
                    pos,
                    cap,
                    seek_state: rseek_state,
                },
            buf: wbuf,
            written,
            seek_state: wseek_state,
        } = b;

        BufStream {
            inner: BufReader {
                inner: BufWriter {
                    inner,
                    buf: wbuf,
                    written,
                    seek_state: wseek_state,
                },
                buf: rbuf,
                pos,
                cap,
                seek_state: rseek_state,
            },
        }
    }
}

impl<RW: AsyncRead + AsyncWrite> AsyncWrite for BufStream<RW> {
    fn poll_write(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &[u8],
    ) -> Poll<io::Result<usize>> {
        self.project().inner.poll_write(cx, buf)
    }

    fn poll_write_vectored(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        bufs: &[IoSlice<'_>],
    ) -> Poll<io::Result<usize>> {
        self.project().inner.poll_write_vectored(cx, bufs)
    }

    fn is_write_vectored(&self) -> bool {
        self.inner.is_write_vectored()
    }

    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        self.project().inner.poll_flush(cx)
    }

    fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        self.project().inner.poll_shutdown(cx)
    }
}

impl<RW: AsyncRead + AsyncWrite> AsyncRead for BufStream<RW> {
    fn poll_read(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &mut ReadBuf<'_>,
    ) -> Poll<io::Result<()>> {
        self.project().inner.poll_read(cx, buf)
    }
}

/// Seek to an offset, in bytes, in the underlying stream.
///
/// The position used for seeking with `SeekFrom::Current(_)` is the
/// position the underlying stream would be at if the `BufStream` had no
/// internal buffer.
///
/// Seeking always discards the internal buffer, even if the seek position
/// would otherwise fall within it. This guarantees that calling
/// `.into_inner()` immediately after a seek yields the underlying reader
/// at the same position.
///
/// See [`AsyncSeek`] for more details.
///
/// Note: In the edge case where you're seeking with `SeekFrom::Current(n)`
/// where `n` minus the internal buffer length overflows an `i64`, two
/// seeks will be performed instead of one. If the second seek returns
/// `Err`, the underlying reader will be left at the same position it would
/// have if you called `seek` with `SeekFrom::Current(0)`.
impl<RW: AsyncRead + AsyncWrite + AsyncSeek> AsyncSeek for BufStream<RW> {
    fn start_seek(self: Pin<&mut Self>, position: SeekFrom) -> io::Result<()> {
        self.project().inner.start_seek(position)
    }

    fn poll_complete(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>> {
        self.project().inner.poll_complete(cx)
    }
}

impl<RW: AsyncRead + AsyncWrite> AsyncBufRead for BufStream<RW> {
    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
        self.project().inner.poll_fill_buf(cx)
    }

    fn consume(self: Pin<&mut Self>, amt: usize) {
        self.project().inner.consume(amt)
    }
}

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

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