Merge pull request #48 from oberien/read_until

feat(io): Add `read_until`

src/io/mod.rs

@@ -36,6 +36,7 @@ mod flush;
 mod read_exact;
 mod read_to_end;
 mod read;
+mod read_until;
 mod split;
 mod window;
 mod write_all;
@@ -44,6 +45,7 @@ pub use self::flush::{flush, Flush};
 pub use self::read_exact::{read_exact, ReadExact};
 pub use self::read_to_end::{read_to_end, ReadToEnd};
 pub use self::read::read;
+pub use self::read_until::{read_until, ReadUntil};
 pub use self::split::{ReadHalf, WriteHalf};
 pub use self::window::Window;
 pub use self::write_all::{write_all, WriteAll};

src/io/read_until.rs

@@ -0,0 +1,70 @@
+use std::io::{self, Read, BufRead};
+use std::mem;
+
+use futures::{Poll, Future};
+
+/// A future which can be used to easily read the contents of a stream into a 
+/// vector until the delimiter is reached.
+///
+/// Created by the [`read_until`] function.
+///
+/// [`read_until`]: fn.read_until.html
+pub struct ReadUntil<A> {
+    state: State<A>,
+}
+
+enum State<A> {
+    Reading {
+        a: A,
+        byte: u8,
+        buf: Vec<u8>,
+    },
+    Empty,
+}
+
+/// Creates a future which will read all the bytes associated with the I/O
+/// object `A` into the buffer provided until the delimiter `byte` is reached.
+/// This method is the async equivalent to [`BufRead::read_until`].
+///
+/// In case of an error the buffer and the object will be discarded, with
+/// the error yielded. In the case of success the object will be destroyed and
+/// the buffer will be returned, with all bytes up to, and including, the delimiter
+/// (if found).
+///
+/// [`ButRead::read_until`]: https://doc.rust-lang.org/std/io/trait.BufRead.html#method.read_until
+pub fn read_until<A>(a: A, byte: u8, buf: Vec<u8>) -> ReadUntil<A>
+    where A: BufRead
+{
+    ReadUntil {
+        state: State::Reading {
+            a: a,
+            byte: byte,
+            buf: buf,
+        }
+    }
+}
+
+impl<A> Future for ReadUntil<A>
+    where A: Read + BufRead
+{
+    type Item = (A, Vec<u8>);
+    type Error = io::Error;
+
+    fn poll(&mut self) -> Poll<(A, Vec<u8>), io::Error> {
+        match self.state {
+            State::Reading { ref mut a, byte, ref mut buf } => {
+                // If we get `Ok(n)`, then we know the stream hit EOF or the delimiter.
+                // and just return it, as we are finished.
+                // If we hit "would block" then all the read data so far
+                // is in our buffer, and otherwise we propagate errors.
+                try_nb!(a.read_until(byte, buf));
+            },
+            State::Empty => panic!("poll ReadUntil after it's done"),
+        }
+
+        match mem::replace(&mut self.state, State::Empty) {
+            State::Reading { a, byte: _, buf } => Ok((a, buf).into()),
+            State::Empty => unreachable!(),
+        }
+    }
+}