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
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
use crate::io::sys;
use crate::io::{AsyncRead, AsyncWrite, ReadBuf};

use std::cmp;
use std::future::Future;
use std::io;
use std::io::prelude::*;
use std::pin::Pin;
use std::task::{ready, Context, Poll};

/// `T` should not implement _both_ Read and Write.
#[derive(Debug)]
pub(crate) struct Blocking<T> {
    inner: Option<T>,
    state: State<T>,
    /// `true` if the lower IO layer needs flushing.
    need_flush: bool,
}

#[derive(Debug)]
pub(crate) struct Buf {
    buf: Vec<u8>,
    pos: usize,
}

pub(crate) const DEFAULT_MAX_BUF_SIZE: usize = 2 * 1024 * 1024;

#[derive(Debug)]
enum State<T> {
    Idle(Option<Buf>),
    Busy(sys::Blocking<(io::Result<usize>, Buf, T)>),
}

cfg_io_blocking! {
    impl<T> Blocking<T> {
        #[cfg_attr(feature = "fs", allow(dead_code))]
        pub(crate) fn new(inner: T) -> Blocking<T> {
            Blocking {
                inner: Some(inner),
                state: State::Idle(Some(Buf::with_capacity(0))),
                need_flush: false,
            }
        }
    }
}

impl<T> AsyncRead for Blocking<T>
where
    T: Read + Unpin + Send + 'static,
{
    fn poll_read(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        dst: &mut ReadBuf<'_>,
    ) -> Poll<io::Result<()>> {
        loop {
            match self.state {
                State::Idle(ref mut buf_cell) => {
                    let mut buf = buf_cell.take().unwrap();

                    if !buf.is_empty() {
                        buf.copy_to(dst);
                        *buf_cell = Some(buf);
                        return Poll::Ready(Ok(()));
                    }

                    buf.ensure_capacity_for(dst, DEFAULT_MAX_BUF_SIZE);
                    let mut inner = self.inner.take().unwrap();

                    self.state = State::Busy(sys::run(move || {
                        let res = buf.read_from(&mut inner);
                        (res, buf, inner)
                    }));
                }
                State::Busy(ref mut rx) => {
                    let (res, mut buf, inner) = ready!(Pin::new(rx).poll(cx))?;
                    self.inner = Some(inner);

                    match res {
                        Ok(_) => {
                            buf.copy_to(dst);
                            self.state = State::Idle(Some(buf));
                            return Poll::Ready(Ok(()));
                        }
                        Err(e) => {
                            assert!(buf.is_empty());

                            self.state = State::Idle(Some(buf));
                            return Poll::Ready(Err(e));
                        }
                    }
                }
            }
        }
    }
}

impl<T> AsyncWrite for Blocking<T>
where
    T: Write + Unpin + Send + 'static,
{
    fn poll_write(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        src: &[u8],
    ) -> Poll<io::Result<usize>> {
        loop {
            match self.state {
                State::Idle(ref mut buf_cell) => {
                    let mut buf = buf_cell.take().unwrap();

                    assert!(buf.is_empty());

                    let n = buf.copy_from(src, DEFAULT_MAX_BUF_SIZE);
                    let mut inner = self.inner.take().unwrap();

                    self.state = State::Busy(sys::run(move || {
                        let n = buf.len();
                        let res = buf.write_to(&mut inner).map(|()| n);

                        (res, buf, inner)
                    }));
                    self.need_flush = true;

                    return Poll::Ready(Ok(n));
                }
                State::Busy(ref mut rx) => {
                    let (res, buf, inner) = ready!(Pin::new(rx).poll(cx))?;
                    self.state = State::Idle(Some(buf));
                    self.inner = Some(inner);

                    // If error, return
                    res?;
                }
            }
        }
    }

    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
        loop {
            let need_flush = self.need_flush;
            match self.state {
                // The buffer is not used here
                State::Idle(ref mut buf_cell) => {
                    if need_flush {
                        let buf = buf_cell.take().unwrap();
                        let mut inner = self.inner.take().unwrap();

                        self.state = State::Busy(sys::run(move || {
                            let res = inner.flush().map(|()| 0);
                            (res, buf, inner)
                        }));

                        self.need_flush = false;
                    } else {
                        return Poll::Ready(Ok(()));
                    }
                }
                State::Busy(ref mut rx) => {
                    let (res, buf, inner) = ready!(Pin::new(rx).poll(cx))?;
                    self.state = State::Idle(Some(buf));
                    self.inner = Some(inner);

                    // If error, return
                    res?;
                }
            }
        }
    }

    fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
        Poll::Ready(Ok(()))
    }
}

/// Repeats operations that are interrupted.
macro_rules! uninterruptibly {
    ($e:expr) => {{
        loop {
            match $e {
                Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {}
                res => break res,
            }
        }
    }};
}

impl Buf {
    pub(crate) fn with_capacity(n: usize) -> Buf {
        Buf {
            buf: Vec::with_capacity(n),
            pos: 0,
        }
    }

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

    pub(crate) fn len(&self) -> usize {
        self.buf.len() - self.pos
    }

    pub(crate) fn copy_to(&mut self, dst: &mut ReadBuf<'_>) -> usize {
        let n = cmp::min(self.len(), dst.remaining());
        dst.put_slice(&self.bytes()[..n]);
        self.pos += n;

        if self.pos == self.buf.len() {
            self.buf.truncate(0);
            self.pos = 0;
        }

        n
    }

    pub(crate) fn copy_from(&mut self, src: &[u8], max_buf_size: usize) -> usize {
        assert!(self.is_empty());

        let n = cmp::min(src.len(), max_buf_size);

        self.buf.extend_from_slice(&src[..n]);
        n
    }

    pub(crate) fn bytes(&self) -> &[u8] {
        &self.buf[self.pos..]
    }

    pub(crate) fn ensure_capacity_for(&mut self, bytes: &ReadBuf<'_>, max_buf_size: usize) {
        assert!(self.is_empty());

        let len = cmp::min(bytes.remaining(), max_buf_size);

        if self.buf.len() < len {
            self.buf.reserve(len - self.buf.len());
        }

        unsafe {
            self.buf.set_len(len);
        }
    }

    pub(crate) fn read_from<T: Read>(&mut self, rd: &mut T) -> io::Result<usize> {
        let res = uninterruptibly!(rd.read(&mut self.buf));

        if let Ok(n) = res {
            self.buf.truncate(n);
        } else {
            self.buf.clear();
        }

        assert_eq!(self.pos, 0);

        res
    }

    pub(crate) fn write_to<T: Write>(&mut self, wr: &mut T) -> io::Result<()> {
        assert_eq!(self.pos, 0);

        // `write_all` already ignores interrupts
        let res = wr.write_all(&self.buf);
        self.buf.clear();
        res
    }
}

cfg_fs! {
    impl Buf {
        pub(crate) fn discard_read(&mut self) -> i64 {
            let ret = -(self.bytes().len() as i64);
            self.pos = 0;
            self.buf.truncate(0);
            ret
        }

        pub(crate) fn copy_from_bufs(&mut self, bufs: &[io::IoSlice<'_>], max_buf_size: usize) -> usize {
            assert!(self.is_empty());

            let mut rem = max_buf_size;
            for buf in bufs {
                if rem == 0 {
                    break
                }

                let len = buf.len().min(rem);
                self.buf.extend_from_slice(&buf[..len]);
                rem -= len;
            }

            max_buf_size - rem
        }
    }
}