Split out starting a listener from accepting incoming connections.

The Listener trait takes two type parameters, the type of connection and the type of Acceptor,
and specifies only one method, listen, which consumes the listener and produces an Acceptor.

The Acceptor trait takes one type parameter, the type of connection, and defines two methods.
The accept() method waits for an incoming connection attempt and returns the result.
The incoming() method creates an iterator over incoming connections and is a default method.

Example:

let listener = TcpListener.bind(addr); // Bind to a socket
let acceptor = listener.listen(); // Start the listener
for stream in acceptor.incoming() {
    // Process incoming connections forever (or until you break out of the loop)
}

src/libstd/rt/io/mod.rs

@@ -474,17 +474,43 @@ pub trait Seek {
     fn seek(&mut self, pos: i64, style: SeekStyle);
 }
 
-/// A listener is a value that listens for connections
-pub trait Listener<S> {
-    /// Wait for and accept an incoming connection
-    ///
-    /// Returns `None` on timeout.
+/// A listener is a value that can consume itself to start listening for connections.
+/// Doing so produces some sort of Acceptor.
+pub trait Listener<T, A: Acceptor<T>> {
+    /// Spin up the listener and start queueing incoming connections
     ///
     /// # Failure
     ///
     /// Raises `io_error` condition. If the condition is handled,
+    /// then `listen` returns `None`.
+    fn listen(self) -> Option<A>;
+}
+
+/// An acceptor is a value that presents incoming connections
+pub trait Acceptor<T> {
+    /// Wait for and accept an incoming connection
+    ///
+    /// # Failure
+    /// Raise `io_error` condition. If the condition is handled,
     /// then `accept` returns `None`.
-    fn accept(&mut self) -> Option<S>;
+    fn accept(&mut self) -> Option<T>;
+
+    /// Create an iterator over incoming connections
+    fn incoming<'r>(&'r mut self) -> IncomingIterator<'r, Self> {
+        IncomingIterator { inc: self }
+    }
+}
+
+/// An infinite iterator over incoming connection attempts.
+/// Calling `next` will block the task until a connection is attempted.
+struct IncomingIterator<'self, A> {
+    priv inc: &'self mut A,
+}
+
+impl<'self, T, A: Acceptor<T>> Iterator<T> for IncomingIterator<'self, A> {
+    fn next(&mut self) -> Option<T> {
+        self.inc.accept()
+    }
 }
 
 /// Common trait for decorator types.

src/libstd/rt/io/net/tcp.rs

@@ -11,12 +11,13 @@
 use option::{Option, Some, None};
 use result::{Ok, Err};
 use rt::io::net::ip::SocketAddr;
-use rt::io::{Reader, Writer, Listener};
+use rt::io::{Reader, Writer, Listener, Acceptor};
 use rt::io::{io_error, read_error, EndOfFile};
 use rt::rtio::{IoFactory, IoFactoryObject,
-               RtioSocket, RtioTcpListener,
-               RtioTcpListenerObject, RtioTcpStream,
-               RtioTcpStreamObject};
+               RtioSocket,
+               RtioTcpListener, RtioTcpListenerObject,
+               RtioTcpAcceptor, RtioTcpAcceptorObject,
+               RtioTcpStream, RtioTcpStreamObject};
 use rt::local::Local;
 
 pub struct TcpStream(~RtioTcpStreamObject);
@@ -124,13 +125,27 @@ impl TcpListener {
     }
 }
 
-impl Listener<TcpStream> for TcpListener {
+impl Listener<TcpStream, TcpAcceptor> for TcpListener {
+    fn listen(self) -> Option<TcpAcceptor> {
+        match (**self).listen() {
+            Ok(acceptor) => Some(TcpAcceptor(acceptor)),
+            Err(ioerr) => {
+                io_error::cond.raise(ioerr);
+                None
+            }
+        }
+    }
+}
+
+pub struct TcpAcceptor(~RtioTcpAcceptorObject);
+
+impl Acceptor<TcpStream> for TcpAcceptor {
     fn accept(&mut self) -> Option<TcpStream> {
         match (**self).accept() {
             Ok(s) => Some(TcpStream::new(s)),
             Err(ioerr) => {
                 io_error::cond.raise(ioerr);
-                return None;
+                None
             }
         }
     }
@@ -184,8 +199,8 @@ mod test {
             let addr = next_test_ip4();
 
             do spawntask {
-                let mut listener = TcpListener::bind(addr);
-                let mut stream = listener.accept();
+                let mut acceptor = TcpListener::bind(addr).listen();
+                let mut stream = acceptor.accept();
                 let mut buf = [0];
                 stream.read(buf);
                 assert!(buf[0] == 99);
@@ -204,8 +219,8 @@ mod test {
             let addr = next_test_ip6();
 
             do spawntask {
-                let mut listener = TcpListener::bind(addr);
-                let mut stream = listener.accept();
+                let mut acceptor = TcpListener::bind(addr).listen();
+                let mut stream = acceptor.accept();
                 let mut buf = [0];
                 stream.read(buf);
                 assert!(buf[0] == 99);
@@ -224,8 +239,8 @@ mod test {
             let addr = next_test_ip4();
 
             do spawntask {
-                let mut listener = TcpListener::bind(addr);
-                let mut stream = listener.accept();
+                let mut acceptor = TcpListener::bind(addr).listen();
+                let mut stream = acceptor.accept();
                 let mut buf = [0];
                 let nread = stream.read(buf);
                 assert!(nread.is_none());
@@ -244,8 +259,8 @@ mod test {
             let addr = next_test_ip6();
 
             do spawntask {
-                let mut listener = TcpListener::bind(addr);
-                let mut stream = listener.accept();
+                let mut acceptor = TcpListener::bind(addr).listen();
+                let mut stream = acceptor.accept();
                 let mut buf = [0];
                 let nread = stream.read(buf);
                 assert!(nread.is_none());
@@ -265,8 +280,8 @@ mod test {
             let addr = next_test_ip4();
 
             do spawntask {
-                let mut listener = TcpListener::bind(addr);
-                let mut stream = listener.accept();
+                let mut acceptor = TcpListener::bind(addr).listen();
+                let mut stream = acceptor.accept();
                 let mut buf = [0];
                 let nread = stream.read(buf);
                 assert!(nread.is_none());
@@ -288,8 +303,8 @@ mod test {
             let addr = next_test_ip6();
 
             do spawntask {
-                let mut listener = TcpListener::bind(addr);
-                let mut stream = listener.accept();
+                let mut acceptor = TcpListener::bind(addr).listen();
+                let mut stream = acceptor.accept();
                 let mut buf = [0];
                 let nread = stream.read(buf);
                 assert!(nread.is_none());
@@ -311,8 +326,8 @@ mod test {
             let addr = next_test_ip4();
 
             do spawntask {
-                let mut listener = TcpListener::bind(addr);
-                let mut stream = listener.accept();
+                let mut acceptor = TcpListener::bind(addr).listen();
+                let mut stream = acceptor.accept();
                 let buf = [0];
                 loop {
                     let mut stop = false;
@@ -341,8 +356,8 @@ mod test {
             let addr = next_test_ip6();
 
             do spawntask {
-                let mut listener = TcpListener::bind(addr);
-                let mut stream = listener.accept();
+                let mut acceptor = TcpListener::bind(addr).listen();
+                let mut stream = acceptor.accept();
                 let buf = [0];
                 loop {
                     let mut stop = false;
@@ -371,9 +386,8 @@ mod test {
             let max = 10;
 
             do spawntask {
-                let mut listener = TcpListener::bind(addr);
-                do max.times {
-                    let mut stream = listener.accept();
+                let mut acceptor = TcpListener::bind(addr).listen();
+                for ref mut stream in acceptor.incoming().take(max) {
                     let mut buf = [0];
                     stream.read(buf);
                     assert_eq!(buf[0], 99);
@@ -396,9 +410,8 @@ mod test {
             let max = 10;
 
             do spawntask {
-                let mut listener = TcpListener::bind(addr);
-                do max.times {
-                    let mut stream = listener.accept();
+                let mut acceptor = TcpListener::bind(addr).listen();
+                for ref mut stream in acceptor.incoming().take(max) {
                     let mut buf = [0];
                     stream.read(buf);
                     assert_eq!(buf[0], 99);
@@ -421,10 +434,9 @@ mod test {
             static MAX: int = 10;
 
             do spawntask {
-                let mut listener = TcpListener::bind(addr);
-                for i in range(0, MAX) {
-                    let stream = Cell::new(listener.accept());
-                    rtdebug!("accepted");
+                let mut acceptor = TcpListener::bind(addr).listen();
+                for (i, stream) in acceptor.incoming().enumerate().take(MAX as uint) {
+                    let stream = Cell::new(stream);
                     // Start another task to handle the connection
                     do spawntask {
                         let mut stream = stream.take();
@@ -460,10 +472,9 @@ mod test {
             static MAX: int = 10;
 
             do spawntask {
-                let mut listener = TcpListener::bind(addr);
-                for i in range(0, MAX) {
-                    let stream = Cell::new(listener.accept());
-                    rtdebug!("accepted");
+                let mut acceptor = TcpListener::bind(addr).listen();
+                for (i, stream) in acceptor.incoming().enumerate().take(MAX as uint) {
+                    let stream = Cell::new(stream);
                     // Start another task to handle the connection
                     do spawntask {
                         let mut stream = stream.take();
@@ -499,10 +510,9 @@ mod test {
             static MAX: int = 10;
 
             do spawntask {
-                let mut listener = TcpListener::bind(addr);
-                for _ in range(0, MAX) {
-                    let stream = Cell::new(listener.accept());
-                    rtdebug!("accepted");
+                let mut acceptor = TcpListener::bind(addr).listen();
+                for stream in acceptor.incoming().take(MAX as uint) {
+                    let stream = Cell::new(stream);
                     // Start another task to handle the connection
                     do spawntask_later {
                         let mut stream = stream.take();
@@ -537,10 +547,9 @@ mod test {
             static MAX: int = 10;
 
             do spawntask {
-                let mut listener = TcpListener::bind(addr);
-                for _ in range(0, MAX) {
-                    let stream = Cell::new(listener.accept());
-                    rtdebug!("accepted");
+                let mut acceptor = TcpListener::bind(addr).listen();
+                for stream in acceptor.incoming().take(MAX as uint) {
+                    let stream = Cell::new(stream);
                     // Start another task to handle the connection
                     do spawntask_later {
                         let mut stream = stream.take();
@@ -573,10 +582,7 @@ mod test {
     fn socket_name(addr: SocketAddr) {
         do run_in_newsched_task {
             do spawntask {
-                let listener = TcpListener::bind(addr);
-
-                assert!(listener.is_some());
-                let mut listener = listener.unwrap();
+                let mut listener = TcpListener::bind(addr).unwrap();
 
                 // Make sure socket_name gives
                 // us the socket we binded to.
@@ -592,9 +598,9 @@ mod test {
     fn peer_name(addr: SocketAddr) {
         do run_in_newsched_task {
             do spawntask {
-                let mut listener = TcpListener::bind(addr);
+                let mut acceptor = TcpListener::bind(addr).listen();
 
-                listener.accept();
+                acceptor.accept();
             }
 
             do spawntask {

src/libstd/rt/io/net/unix.rs

@@ -40,6 +40,12 @@ impl UnixListener {
     }
 }
 
-impl Listener<UnixStream> for UnixListener {
+impl Listener<UnixStream, UnixAcceptor> for UnixListener {
+    fn listen(self) -> Option<UnixAcceptor> { fail!() }
+}
+
+pub struct UnixAcceptor;
+
+impl Acceptor<UnixStream> for UnixAcceptor {
     fn accept(&mut self) -> Option<UnixStream> { fail!() }
 }

src/libstd/rt/io/option.rs

@@ -17,7 +17,7 @@
 //! # XXX Seek and Close
 
 use option::*;
-use super::{Reader, Writer, Listener};
+use super::{Reader, Writer, Listener, Acceptor};
 use super::{standard_error, PreviousIoError, io_error, read_error, IoError};
 
 fn prev_io_error() -> IoError {
@@ -62,10 +62,22 @@ impl<R: Reader> Reader for Option<R> {
     }
 }
 
-impl<L: Listener<S>, S> Listener<S> for Option<L> {
-    fn accept(&mut self) -> Option<S> {
+impl<T, A: Acceptor<T>, L: Listener<T, A>> Listener<T, A> for Option<L> {
+    fn listen(self) -> Option<A> {
+        match self {
+            Some(listener) => listener.listen(),
+            None => {
+                io_error::cond.raise(prev_io_error());
+                None
+            }
+        }
+    }
+}
+
+impl<T, A: Acceptor<T>> Acceptor<T> for Option<A> {
+    fn accept(&mut self) -> Option<T> {
         match *self {
-            Some(ref mut listener) => listener.accept(),
+            Some(ref mut acceptor) => acceptor.accept(),
             None => {
                 io_error::cond.raise(prev_io_error());
                 None

src/libstd/rt/rtio.rs

@@ -26,6 +26,7 @@ pub type EventLoopObject = uvio::UvEventLoop;
 pub type RemoteCallbackObject = uvio::UvRemoteCallback;
 pub type IoFactoryObject = uvio::UvIoFactory;
 pub type RtioTcpStreamObject = uvio::UvTcpStream;
+pub type RtioTcpAcceptorObject = uvio::UvTcpAcceptor;
 pub type RtioTcpListenerObject = uvio::UvTcpListener;
 pub type RtioUdpSocketObject = uvio::UvUdpSocket;
 pub type RtioTimerObject = uvio::UvTimer;
@@ -75,6 +76,10 @@ pub trait IoFactory {
 }
 
 pub trait RtioTcpListener : RtioSocket {
+    fn listen(self) -> Result<~RtioTcpAcceptorObject, IoError>;
+}
+
+pub trait RtioTcpAcceptor : RtioSocket {
     fn accept(&mut self) -> Result<~RtioTcpStreamObject, IoError>;
     fn accept_simultaneously(&mut self) -> Result<(), IoError>;
     fn dont_accept_simultaneously(&mut self) -> Result<(), IoError>;