1 files changed, 80 insertions, 0 deletions
diff --git a/tokio/src/io/util/read_line.rs b/tokio/src/io/util/read_line.rs
new file mode 100644
index 00000000..b917bd41
--- /dev/null
+++ b/tokio/src/io/util/read_line.rs
@@ -0,0 +1,80 @@
+use crate::io::util::read_until::read_until_internal;
+use crate::io::AsyncBufRead;
+
+use std::future::Future;
+use std::io;
+use std::mem;
+use std::pin::Pin;
+use std::str;
+use std::task::{Context, Poll};
+
+/// Future for the [`read_line`](crate::io::AsyncBufReadExt::read_line) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct ReadLine<'a, R: ?Sized> {
+    reader: &'a mut R,
+    buf: &'a mut String,
+    bytes: Vec<u8>,
+    read: usize,
+}
+
+pub(crate) fn read_line<'a, R>(reader: &'a mut R, buf: &'a mut String) -> ReadLine<'a, R>
+where
+    R: AsyncBufRead + ?Sized + Unpin,
+{
+    ReadLine {
+        reader,
+        bytes: unsafe { mem::replace(buf.as_mut_vec(), Vec::new()) },
+        buf,
+        read: 0,
+    }
+}
+
+pub(super) fn read_line_internal<R: AsyncBufRead + ?Sized>(
+    reader: Pin<&mut R>,
+    cx: &mut Context<'_>,
+    buf: &mut String,
+    bytes: &mut Vec<u8>,
+    read: &mut usize,
+) -> Poll<io::Result<usize>> {
+    let ret = ready!(read_until_internal(reader, cx, b'\n', bytes, read));
+    if str::from_utf8(&bytes).is_err() {
+        Poll::Ready(ret.and_then(|_| {
+            Err(io::Error::new(
+                io::ErrorKind::InvalidData,
+                "stream did not contain valid UTF-8",
+            ))
+        }))
+    } else {
+        debug_assert!(buf.is_empty());
+        debug_assert_eq!(*read, 0);
+        // Safety: `bytes` is a valid UTF-8 because `str::from_utf8` returned `Ok`.
+        mem::swap(unsafe { buf.as_mut_vec() }, bytes);
+        Poll::Ready(ret)
+    }
+}
+
+impl<R: AsyncBufRead + ?Sized + Unpin> Future for ReadLine<'_, R> {
+    type Output = io::Result<usize>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let Self {
+            reader,
+            buf,
+            bytes,
+            read,
+        } = &mut *self;
+        read_line_internal(Pin::new(reader), cx, buf, bytes, read)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn assert_unpin() {
+        use std::marker::PhantomPinned;
+        crate::is_unpin::<ReadLine<'_, PhantomPinned>>();
+    }
+}