Extract drive combinator to test support

tests/support/src/future_ext.rs

@@ -1,23 +1,43 @@
-use futures::{Future, Poll};
+use futures::{Future, Async, Poll};
 
 use std::fmt;
 
+/// Future extension helpers that are useful for tests
 pub trait FutureExt: Future {
+    /// Panic on error
     fn unwrap(self) -> Unwrap<Self>
         where Self: Sized,
               Self::Error: fmt::Debug,
     {
         Unwrap { inner: self }
     }
-}
 
-pub struct Unwrap<T> {
-    inner: T,
+    /// Drive `other` by polling `self`.
+    ///
+    /// `self` must not resolve before `other` does.
+    fn drive<T>(self, other: T) -> Drive<Self, T>
+        where T: Future,
+              T::Error: fmt::Debug,
+              Self: Future<Item = ()> + Sized,
+              Self::Error: fmt::Debug,
+    {
+        Drive {
+            driver: Some(self),
+            future: other,
+        }
+    }
 }
 
 impl<T: Future> FutureExt for T {
 }
 
+// ===== Unwrap ======
+
+/// Panic on error
+pub struct Unwrap<T> {
+    inner: T,
+}
+
 impl<T> Future for Unwrap<T>
     where T: Future,
           T::Item: fmt::Debug,
@@ -30,3 +50,44 @@ impl<T> Future for Unwrap<T>
         Ok(self.inner.poll().unwrap())
     }
 }
+
+// ===== Drive ======
+
+/// Drive a future to completion while also polling the driver
+///
+/// This is useful for H2 futures that also require the connection to be polled.
+pub struct Drive<T, U> {
+    driver: Option<T>,
+    future: U,
+}
+
+impl<T, U> Future for Drive<T, U>
+    where T: Future<Item = ()>,
+          U: Future,
+          T::Error: fmt::Debug,
+          U::Error: fmt::Debug,
+{
+    type Item = (T, U::Item);
+    type Error = ();
+
+    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
+        match self.future.poll() {
+            Ok(Async::Ready(val)) => {
+                // Get the driver
+                let driver = self.driver.take().unwrap();
+
+                return Ok((driver, val).into())
+            }
+            Ok(_) => {}
+            Err(e) => panic!("unexpected error; {:?}", e),
+        }
+
+        match self.driver.as_mut().unwrap().poll() {
+            Ok(Async::Ready(_)) => panic!("driver resolved before future"),
+            Ok(Async::NotReady) => {}
+            Err(e) => panic!("unexpected error; {:?}", e),
+        }
+
+        Ok(Async::NotReady)
+    }
+}