feat(client): introduce lower-level Connection API

Closes #1449

src/client/tests.rs

@@ -45,3 +45,47 @@ fn retryable_request() {
 
     core.run(res2.join(srv2)).expect("res2");
 }
+
+#[test]
+fn conn_reset_after_write() {
+    let _ = pretty_env_logger::try_init();
+    let mut core = Core::new().unwrap();
+
+    let mut connector = MockConnector::new();
+
+    let sock1 = connector.mock("http://mock.local/a");
+
+    let client = Client::configure()
+        .connector(connector)
+        .build(&core.handle());
+
+
+    {
+        let res1 = client.get("http://mock.local/a".parse().unwrap());
+        let srv1 = poll_fn(|| {
+            try_ready!(sock1.read(&mut [0u8; 512]));
+            try_ready!(sock1.write(b"HTTP/1.1 200 OK\r\nContent-Length: 0\r\n\r\n"));
+            Ok(Async::Ready(()))
+        });
+        core.run(res1.join(srv1)).expect("res1");
+    }
+
+    let res2 = client.get("http://mock.local/a".parse().unwrap());
+    let mut sock1 = Some(sock1);
+    let srv2 = poll_fn(|| {
+        // We purposefully keep the socket open until the client
+        // has written the second request, and THEN disconnect.
+        //
+        // Not because we expect servers to be jerks, but to trigger
+        // state where we write on an assumedly good connetion, and
+        // only reset the close AFTER we wrote bytes.
+        try_ready!(sock1.as_mut().unwrap().read(&mut [0u8; 512]));
+        sock1.take();
+        Ok(Async::Ready(()))
+    });
+    let err = core.run(res2.join(srv2)).expect_err("res2");
+    match err {
+        ::Error::Incomplete => (),
+        other => panic!("expected Incomplete, found {:?}", other)
+    }
+}