tokio: add AsyncBufReadExt::lines

tokio/Cargo.toml

@@ -40,7 +40,7 @@ default = [
 
 codec = ["io", "tokio-codec"]
 fs = ["tokio-fs"]
-io = ["bytes", "tokio-io", "memchr"]
+io = ["bytes", "tokio-io", "tokio-futures", "memchr"]
 reactor = ["io", "tokio-reactor"]
 rt-full = [
   "num_cpus",
@@ -83,7 +83,7 @@ tracing-core = { version = "0.1", optional = true }
 memchr = { version = "2.2", optional = true }
 
 # Needed for async/await preview support
-#tokio-futures = { version = "0.2.0", optional = true, path = "../tokio-futures" }
+tokio-futures = { version = "0.2.0", optional = true, path = "../tokio-futures" }
 
 [target.'cfg(unix)'.dependencies]
 tokio-uds = { version = "0.3.0", optional = true, path = "../tokio-uds" }
@@ -102,3 +102,4 @@ num_cpus = "1.0"
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
 time = "0.1"
+futures-util-preview = "0.3.0-alpha.17"

tokio/src/io/async_buf_read_ext.rs

@@ -1,3 +1,4 @@
+use crate::io::lines::{lines, Lines};
 use crate::io::read_line::{read_line, ReadLine};
 use crate::io::read_until::{read_until, ReadUntil};
 
@@ -66,6 +67,34 @@ pub trait AsyncBufReadExt: AsyncBufRead {
     {
         read_line(self, buf)
     }
+
+    /// Returns a stream over the lines of this reader.
+    /// This method is the async equivalent to [`BufRead::lines`](std::io::BufRead::lines).
+    ///
+    /// The stream returned from this function will yield instances of
+    /// [`io::Result`]`<`[`String`]`>`. Each string returned will *not* have a newline
+    /// byte (the 0xA byte) or CRLF (0xD, 0xA bytes) at the end.
+    ///
+    /// [`io::Result`]: std::io::Result
+    /// [`String`]: String
+    ///
+    /// # Errors
+    ///
+    /// Each line of the stream has the same error semantics as [`AsyncBufReadExt::read_line`].
+    ///
+    /// [`AsyncBufReadExt::read_line`]: AsyncBufReadExt::read_line
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// unimplemented!();
+    /// ```
+    fn lines(self) -> Lines<Self>
+    where
+        Self: Sized,
+    {
+        lines(self)
+    }
 }
 
 impl<R: AsyncBufRead + ?Sized> AsyncBufReadExt for R {}

tokio/src/io/lines.rs

@@ -0,0 +1,56 @@
+use super::read_line::read_line_internal;
+use std::io;
+use std::mem;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+use tokio_futures::Stream;
+use tokio_io::AsyncBufRead;
+
+/// Stream for the [`lines`](crate::io::AsyncBufReadExt::lines) method.
+#[derive(Debug)]
+#[must_use = "streams do nothing unless polled"]
+pub struct Lines<R> {
+    reader: R,
+    buf: String,
+    bytes: Vec<u8>,
+    read: usize,
+}
+
+impl<R: Unpin> Unpin for Lines<R> {}
+
+pub(crate) fn lines<R>(reader: R) -> Lines<R>
+where
+    R: AsyncBufRead,
+{
+    Lines {
+        reader,
+        buf: String::new(),
+        bytes: Vec::new(),
+        read: 0,
+    }
+}
+
+impl<R: AsyncBufRead> Stream for Lines<R> {
+    type Item = io::Result<String>;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let Self {
+            reader,
+            buf,
+            bytes,
+            read,
+        } = unsafe { self.get_unchecked_mut() };
+        let reader = unsafe { Pin::new_unchecked(reader) };
+        let n = ready!(read_line_internal(reader, cx, buf, bytes, read))?;
+        if n == 0 && buf.is_empty() {
+            return Poll::Ready(None);
+        }
+        if buf.ends_with('\n') {
+            buf.pop();
+            if buf.ends_with('\r') {
+                buf.pop();
+            }
+        }
+        Poll::Ready(Some(Ok(mem::replace(buf, String::new()))))
+    }
+}

tokio/src/io/mod.rs

@@ -40,6 +40,7 @@ mod async_buf_read_ext;
 mod async_read_ext;
 mod async_write_ext;
 mod copy;
+mod lines;
 mod read;
 mod read_exact;
 mod read_line;

tokio/tests/io_lines.rs

@@ -0,0 +1,53 @@
+#![deny(warnings, rust_2018_idioms)]
+#![feature(async_await)]
+
+use futures_util::StreamExt;
+use tokio::io::{AsyncBufRead, AsyncBufReadExt, AsyncRead};
+use tokio_test::assert_ok;
+
+use std::io;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+#[tokio::test]
+async fn lines() {
+    struct Rd {
+        val: &'static [u8],
+    }
+
+    impl AsyncRead for Rd {
+        fn poll_read(
+            self: Pin<&mut Self>,
+            _: &mut Context<'_>,
+            _: &mut [u8],
+        ) -> Poll<io::Result<usize>> {
+            unimplemented!()
+        }
+    }
+
+    impl AsyncBufRead for Rd {
+        fn poll_fill_buf<'a>(
+            self: Pin<&'a mut Self>,
+            _: &mut Context<'_>,
+        ) -> Poll<io::Result<&'a [u8]>> {
+            Poll::Ready(Ok(self.val))
+        }
+
+        fn consume(mut self: Pin<&mut Self>, amt: usize) {
+            self.val = &self.val[amt..];
+        }
+    }
+
+    let rd = Rd {
+        val: b"hello\r\nworld\n\n",
+    };
+    let mut st = rd.lines();
+
+    let b = assert_ok!(st.next().await.unwrap());
+    assert_eq!(b, "hello");
+    let b = assert_ok!(st.next().await.unwrap());
+    assert_eq!(b, "world");
+    let b = assert_ok!(st.next().await.unwrap());
+    assert_eq!(b, "");
+    assert!(st.next().await.is_none());
+}