io: Bind to shutdown() for TCP streams

This is something that is plausibly useful, and is provided by libuv. This is
not currently surfaced as part of the `TcpStream` type, but it may possibly
appear in the future. For now only the raw functionality is provided through the
Rtio objects.

src/librustuv/net.rs

@@ -305,6 +305,38 @@ impl rtio::RtioTcpStream for TcpWatcher {
             read_access: self.read_access.clone(),
         } as ~rtio::RtioTcpStream
     }
+
+    fn close_write(&mut self) -> Result<(), IoError> {
+        struct Ctx {
+            slot: Option<BlockedTask>,
+            status: c_int,
+        }
+        let mut req = Request::new(uvll::UV_SHUTDOWN);
+
+        return match unsafe {
+            uvll::uv_shutdown(req.handle, self.handle, shutdown_cb)
+        } {
+            0 => {
+                req.defuse(); // uv callback now owns this request
+                let mut cx = Ctx { slot: None, status: 0 };
+
+                wait_until_woken_after(&mut cx.slot, &self.uv_loop(), || {
+                    req.set_data(&cx);
+                });
+
+                status_to_io_result(cx.status)
+            }
+            n => Err(uv_error_to_io_error(UvError(n)))
+        };
+
+        extern fn shutdown_cb(req: *uvll::uv_shutdown_t, status: libc::c_int) {
+            let req = Request::wrap(req);
+            assert!(status != uvll::ECANCELED);
+            let cx: &mut Ctx = unsafe { req.get_data() };
+            cx.status = status;
+            wakeup(&mut cx.slot);
+        }
+    }
 }
 
 impl UvHandle<uvll::uv_tcp_t> for TcpWatcher {

src/librustuv/uvll.rs

@@ -157,6 +157,7 @@ pub type uv_process_t = c_void;
 pub type uv_pipe_t = c_void;
 pub type uv_tty_t = c_void;
 pub type uv_signal_t = c_void;
+pub type uv_shutdown_t = c_void;
 
 pub struct uv_timespec_t {
     tv_sec: libc::c_long,
@@ -248,6 +249,7 @@ pub type uv_exit_cb = extern "C" fn(handle: *uv_process_t,
 pub type uv_signal_cb = extern "C" fn(handle: *uv_signal_t,
                                       signum: c_int);
 pub type uv_fs_cb = extern "C" fn(req: *uv_fs_t);
+pub type uv_shutdown_cb = extern "C" fn(req: *uv_shutdown_t, status: c_int);
 
 #[cfg(unix)] pub type uv_uid_t = libc::types::os::arch::posix88::uid_t;
 #[cfg(unix)] pub type uv_gid_t = libc::types::os::arch::posix88::gid_t;
@@ -539,6 +541,8 @@ extern {
                          on_alloc: uv_alloc_cb,
                          on_read: uv_read_cb) -> c_int;
     pub fn uv_read_stop(stream: *uv_stream_t) -> c_int;
+    pub fn uv_shutdown(req: *uv_shutdown_t, handle: *uv_stream_t,
+                       cb: uv_shutdown_cb) -> c_int;
 
     // idle bindings
     pub fn uv_idle_init(l: *uv_loop_t, i: *uv_idle_t) -> c_int;