Implement SendRequest::ready. (#215)

This provides a functional future API for waiting for SendRequest
readiness.

src/client.rs

@@ -28,6 +28,13 @@ pub struct SendRequest<B: IntoBuf> {
     pending: Option<proto::StreamKey>,
 }
 
+/// Returns a `SendRequest` instance once it is ready to send at least one
+/// request.
+#[derive(Debug)]
+pub struct ReadySendRequest<B: IntoBuf> {
+    inner: Option<SendRequest<B>>,
+}
+
 /// A future to drive the H2 protocol on a connection.
 ///
 /// This must be placed in an executor to ensure proper connection management.
@@ -78,6 +85,12 @@ where
         Ok(().into())
     }
 
+    /// Consumes `self`, returning a future that returns `self` back once it is
+    /// ready to send a request.
+    pub fn ready(self) -> ReadySendRequest<B> {
+        ReadySendRequest { inner: Some(self) }
+    }
+
     /// Send a request on a new HTTP 2.0 stream
     pub fn send_request(
         &mut self,
@@ -147,6 +160,27 @@ where
     }
 }
 
+// ===== impl ReadySendRequest =====
+
+impl<B> Future for ReadySendRequest<B>
+where B: IntoBuf,
+      B::Buf: 'static,
+{
+    type Item = SendRequest<B>;
+    type Error = ::Error;
+
+    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
+        match self.inner {
+            Some(ref mut send_request) => {
+                let _ = try_ready!(send_request.poll_ready());
+            }
+            None => panic!("called `poll` after future completed"),
+        }
+
+        Ok(self.inner.take().unwrap().into())
+    }
+}
+
 // ===== impl Builder =====
 
 impl Builder {