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

use super::buf_writer::BufWriter;
use futures_core::ready;
use futures_core::task::{Context, Poll};
use futures_io::AsyncWrite;
use futures_io::IoSlice;
use pin_project_lite::pin_project;
use std::io;
use std::pin::Pin;

pin_project! {
/// Wrap a writer, like [`BufWriter`] does, but prioritizes buffering lines
///
/// This was written based on `std::io::LineWriter` which goes into further details
/// explaining the code.
///
/// Buffering is actually done using `BufWriter`. This class will leverage `BufWriter`
/// to write on-each-line.
#[derive(Debug)]
pub struct LineWriter<W: AsyncWrite> {
    #[pin]
    buf_writer: BufWriter<W>,
}
}

impl<W: AsyncWrite> LineWriter<W> {
    /// Create a new `LineWriter` with default buffer capacity. The default is currently 1KB
    /// which was taken from `std::io::LineWriter`
    pub fn new(inner: W) -> LineWriter<W> {
        LineWriter::with_capacity(1024, inner)
    }

    /// Creates a new `LineWriter` with the specified buffer capacity.
    pub fn with_capacity(capacity: usize, inner: W) -> LineWriter<W> {
        LineWriter { buf_writer: BufWriter::with_capacity(capacity, inner) }
    }

    /// Flush `buf_writer` if last char is "new line"
    fn flush_if_completed_line(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        let this = self.project();
        match this.buf_writer.buffer().last().copied() {
            Some(b'\n') => this.buf_writer.flush_buf(cx),
            _ => Poll::Ready(Ok(())),
        }
    }

    /// Returns a reference to `buf_writer`'s internally buffered data.
    pub fn buffer(&self) -> &[u8] {
        self.buf_writer.buffer()
    }

    /// Acquires a reference to the underlying sink or stream that this combinator is
    /// pulling from.
    pub fn get_ref(&self) -> &W {
        self.buf_writer.get_ref()
    }
}

impl<W: AsyncWrite> AsyncWrite for LineWriter<W> {
    fn poll_write(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &[u8],
    ) -> Poll<io::Result<usize>> {
        let mut this = self.as_mut().project();
        let newline_index = match memchr::memrchr(b'\n', buf) {
            None => {
                ready!(self.as_mut().flush_if_completed_line(cx)?);
                return self.project().buf_writer.poll_write(cx, buf);
            }
            Some(newline_index) => newline_index + 1,
        };

        ready!(this.buf_writer.as_mut().poll_flush(cx)?);

        let lines = &buf[..newline_index];

        let flushed = { ready!(this.buf_writer.as_mut().inner_poll_write(cx, lines))? };

        if flushed == 0 {
            return Poll::Ready(Ok(0));
        }

        let tail = if flushed >= newline_index {
            &buf[flushed..]
        } else if newline_index - flushed <= this.buf_writer.capacity() {
            &buf[flushed..newline_index]
        } else {
            let scan_area = &buf[flushed..];
            let scan_area = &scan_area[..this.buf_writer.capacity()];
            match memchr::memrchr(b'\n', scan_area) {
                Some(newline_index) => &scan_area[..newline_index + 1],
                None => scan_area,
            }
        };

        let buffered = this.buf_writer.as_mut().write_to_buf(tail);
        Poll::Ready(Ok(flushed + buffered))
    }

    fn poll_write_vectored(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        bufs: &[IoSlice<'_>],
    ) -> Poll<io::Result<usize>> {
        let mut this = self.as_mut().project();
        // `is_write_vectored()` is handled in original code, but not in this crate
        // see https://github.com/rust-lang/rust/issues/70436

        let last_newline_buf_idx = bufs
            .iter()
            .enumerate()
            .rev()
            .find_map(|(i, buf)| memchr::memchr(b'\n', buf).map(|_| i));
        let last_newline_buf_idx = match last_newline_buf_idx {
            None => {
                ready!(self.as_mut().flush_if_completed_line(cx)?);
                return self.project().buf_writer.poll_write_vectored(cx, bufs);
            }
            Some(i) => i,
        };

        ready!(this.buf_writer.as_mut().poll_flush(cx)?);

        let (lines, tail) = bufs.split_at(last_newline_buf_idx + 1);

        let flushed = { ready!(this.buf_writer.as_mut().inner_poll_write_vectored(cx, lines))? };
        if flushed == 0 {
            return Poll::Ready(Ok(0));
        }

        let lines_len = lines.iter().map(|buf| buf.len()).sum();
        if flushed < lines_len {
            return Poll::Ready(Ok(flushed));
        }

        let buffered: usize = tail
            .iter()
            .filter(|buf| !buf.is_empty())
            .map(|buf| this.buf_writer.as_mut().write_to_buf(buf))
            .take_while(|&n| n > 0)
            .sum();

        Poll::Ready(Ok(flushed + buffered))
    }

    /// Forward to `buf_writer` 's `BufWriter::poll_flush()`
    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        self.as_mut().project().buf_writer.poll_flush(cx)
    }

    /// Forward to `buf_writer` 's `BufWriter::poll_close()`
    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        self.as_mut().project().buf_writer.poll_close(cx)
    }
}