Keep polling in Buffered if there's more futures

We're not NotReady until we hit the final future and it's not done.

tests/stream-buffered.rs

@@ -0,0 +1,55 @@
+extern crate futures;
+extern crate futures_io;
+extern crate futures_mio;
+extern crate env_logger;
+
+use std::net::TcpStream;
+use std::thread;
+use std::io::{Read, Write};
+
+use futures::Future;
+use futures::stream::Stream;
+use futures_io::{copy, TaskIo};
+
+macro_rules! t {
+    ($e:expr) => (match $e {
+        Ok(e) => e,
+        Err(e) => panic!("{} failed with {:?}", stringify!($e), e),
+    })
+}
+
+#[test]
+fn echo_server() {
+    drop(env_logger::init());
+
+    let mut l = t!(futures_mio::Loop::new());
+    let srv = l.handle().tcp_listen(&"127.0.0.1:0".parse().unwrap());
+    let srv = t!(l.run(srv));
+    let addr = t!(srv.local_addr());
+
+    let t = thread::spawn(move || {
+        let mut s1 = t!(TcpStream::connect(&addr));
+        let mut s2 = t!(TcpStream::connect(&addr));
+
+        let msg = b"foo";
+        assert_eq!(t!(s1.write(msg)), msg.len());
+        assert_eq!(t!(s2.write(msg)), msg.len());
+        let mut buf = [0; 1024];
+        assert_eq!(t!(s1.read(&mut buf)), msg.len());
+        assert_eq!(&buf[..msg.len()], msg);
+        assert_eq!(t!(s2.read(&mut buf)), msg.len());
+        assert_eq!(&buf[..msg.len()], msg);
+    });
+
+    let future = srv.incoming()
+                    .and_then(|s| TaskIo::new(s.0))
+                    .map(|i| i.split())
+                    .map(|(a,b)| copy(a,b).map(|_| ()))
+                    .buffered(10)
+                    .take(2)
+                    .collect();
+
+    t!(l.run(future));
+
+    t.join().unwrap();
+}