1 files changed, 77 insertions, 0 deletions
diff --git a/src/io/read_exact.rs b/src/io/read_exact.rs
new file mode 100644
index 00000000..b251bfea
--- /dev/null
+++ b/src/io/read_exact.rs
@@ -0,0 +1,77 @@
+use std::io::{self, Read};
+use std::mem;
+
+use futures::{Poll, Future};
+
+/// A future which can be used to easily read the entire contents of a stream
+/// into a vector.
+///
+/// Created by the `read_exact` function.
+pub struct ReadExact<A, T> {
+    state: State<A, T>,
+}
+
+enum State<A, T> {
+    Reading {
+        a: A,
+        buf: T,
+        pos: usize,
+    },
+    Empty,
+}
+
+/// Creates a future which will read exactly enough bytes to fill `buf`,
+/// returning an error if EOF is hit sooner.
+///
+/// The returned future will resolve to both the I/O stream as well as the
+/// buffer once the read operation is completed.
+///
+/// In the 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 data read from the stream appended to
+/// the buffer.
+pub fn read_exact<A, T>(a: A, buf: T) -> ReadExact<A, T>
+    where A: Read,
+          T: AsMut<[u8]>,
+{
+    ReadExact {
+        state: State::Reading {
+            a: a,
+            buf: buf,
+            pos: 0,
+        },
+    }
+}
+
+fn eof() -> io::Error {
+    io::Error::new(io::ErrorKind::UnexpectedEof, "early eof")
+}
+
+impl<A, T> Future for ReadExact<A, T>
+    where A: Read,
+          T: AsMut<[u8]>,
+{
+    type Item = (A, T);
+    type Error = io::Error;
+
+    fn poll(&mut self) -> Poll<(A, T), io::Error> {
+        match self.state {
+            State::Reading { ref mut a, ref mut buf, ref mut pos } => {
+                let buf = buf.as_mut();
+                while *pos < buf.len() {
+                    let n = try_nb!(a.read(&mut buf[*pos..]));
+                    *pos += n;
+                    if n == 0 {
+                        return Poll::Err(eof())
+                    }
+                }
+            }
+            State::Empty => panic!("poll a WriteAll after it's done"),
+        }
+
+        match mem::replace(&mut self.state, State::Empty) {
+            State::Reading { a, buf, .. } => Poll::Ok((a, buf)),
+            State::Empty => panic!(),
+        }
+    }
+}