Bug 1487985: webdriver: stop throwing away error causes; r=whimboo

Instead of using a catch-all that ignores the error cause, we can
print the cause as part of the panic.

Eventually the error handling in this function should be fixed to
not panic at all, obviously.

testing/webdriver/src/server.rs

@@ -174,7 +174,7 @@ impl<U: WebDriverExtensionRoute + 'static> Service for HttpHandler<U> {
     type ResBody = Body;
 
     type Error = hyper::Error;
-    type Future = Box<future::Future<Item=Response<Self::ResBody>, Error=hyper::Error> + Send>;
+    type Future = Box<future::Future<Item = Response<Self::ResBody>, Error = hyper::Error> + Send>;
 
     fn call(&mut self, req: Request<Self::ReqBody>) -> Self::Future {
         let uri = req.uri().clone();
@@ -191,7 +191,7 @@ impl<U: WebDriverExtensionRoute + 'static> Service for HttpHandler<U> {
                 // matter as long as we are only handling one request at a time.
                 match api.lock() {
                     Ok(ref api) => api.decode_request(method, &uri.path(), &body[..]),
-                    Err(_) => panic!("Something terrible happened"),
+                    Err(e) => panic!("Error decoding request: {:?}", e),
                 }
             };
 
@@ -200,13 +200,10 @@ impl<U: WebDriverExtensionRoute + 'static> Service for HttpHandler<U> {
                     let (send_res, recv_res) = channel();
                     match chan.lock() {
                         Ok(ref c) => {
-                            let res =
-                                c.send(DispatchMessage::HandleWebDriver(message, send_res));
+                            let res = c.send(DispatchMessage::HandleWebDriver(message, send_res));
                             match res {
                                 Ok(x) => x,
-                                Err(_) => {
-                                    panic!("Something terrible happened");
-                                }
+                                Err(e) => panic!("Error: {:?}", e),
                             }
                         }
                         Err(e) => panic!("Error reading response: {:?}", e),
@@ -217,14 +214,12 @@ impl<U: WebDriverExtensionRoute + 'static> Service for HttpHandler<U> {
                             Ok(response) => {
                                 (StatusCode::OK, serde_json::to_string(&response).unwrap())
                             }
-                            Err(err) => {
-                                (err.http_status(), serde_json::to_string(&err).unwrap())
-                            }
+                            Err(e) => (e.http_status(), serde_json::to_string(&e).unwrap()),
                         },
                         Err(e) => panic!("Error reading response: {:?}", e),
                     }
                 }
-                Err(err) => (err.http_status(), serde_json::to_string(&err).unwrap()),
+                Err(e) => (e.http_status(), serde_json::to_string(&e).unwrap()),
             };
 
             debug!("<- {} {}", status, resp_body);