feat(server): change Incoming to iterator over Connections

A connection is returned from Incoming.next(), and can be passed to a
separate thread before any parsing happens. Call conn.open() to get a
Result<(Request, Response)>.

BREAKING CHANGE

examples/concurrent-server.rs

@@ -11,21 +11,6 @@ use hyper::server::{Server, Handler, Incoming, Request, Response};
 use hyper::header::common::ContentLength;
 use hyper::net::{HttpStream, HttpAcceptor, Fresh};
 
-trait ConcurrentHandler: Send + Sync {
-    fn handle(&self, req: Request, res: Response<Fresh>);
-}
-
-struct Concurrent<H: ConcurrentHandler> { handler: Arc<H> }
-
-impl<H: ConcurrentHandler> Handler<HttpAcceptor, HttpStream> for Concurrent<H> {
-    fn handle(self, mut incoming: Incoming) {
-        for (mut req, mut res) in incoming {
-            let clone = self.handler.clone();
-            spawn(proc() { clone.handle(req, res) })
-        }
-    }
-}
-
 macro_rules! try_abort(
     ($e:expr) => {{
         match $e {
@@ -35,6 +20,24 @@ macro_rules! try_abort(
     }}
 )
 
+trait ConcurrentHandler: Send + Sync {
+    fn handle(&self, req: Request, res: Response<Fresh>);
+}
+
+struct Concurrent<H: ConcurrentHandler> { handler: Arc<H> }
+
+impl<H: ConcurrentHandler> Handler<HttpAcceptor, HttpStream> for Concurrent<H> {
+    fn handle(self, mut incoming: Incoming) {
+        for conn in incoming {
+            let clone = self.handler.clone();
+            spawn(proc() {
+                let (req, res) = try_abort!(conn.open());
+                clone.handle(req, res);
+            })
+        }
+    }
+}
+
 struct Echo;
 
 impl ConcurrentHandler for Echo {

examples/hello.rs

@@ -8,8 +8,9 @@ static PHRASE: &'static [u8] = b"Hello World!";
 fn hyper_handle(mut incoming: hyper::server::Incoming) {
     let mut pool = TaskPool::new(100, || { proc(_) { } });
 
-    for (_, mut res) in incoming {
+    for conn in incoming {
         pool.execute(proc(_) {
+            let (_, res) = conn.open().unwrap();
             let mut res = res.start().unwrap();
             res.write(PHRASE).unwrap();
             res.end().unwrap();

examples/server.rs

@@ -19,7 +19,8 @@ macro_rules! try_continue(
 )
 
 fn echo(mut incoming: Incoming) {
-    for (mut req, mut res) in incoming {
+    for conn in incoming {
+        let (mut req, mut res) = try_continue!(conn.open());
         match req.uri {
             hyper::uri::AbsolutePath(ref path) => match (&req.method, path.as_slice()) {
                 (&Get, "/") | (&Get, "/echo") => {