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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)
}
}
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