Add a bad_request response type. Use it when form's aren't utf8.

codegen/src/decorators/route.rs

@@ -94,7 +94,7 @@ impl RouteGenerateExt for RouteParams {
         let expr = quote_expr!(ecx,
             match ::std::str::from_utf8(_req.data.as_slice()) {
                 Ok(s) => s,
-                Err(_) => return ::rocket::Response::server_error()
+                Err(_) => return ::rocket::Response::bad_request("form isn't utf8")
             }
         );
 

lib/src/response/mod.rs

@@ -52,9 +52,15 @@ impl<'a> Response<'a> {
         Response(Box::new(Empty::new(StatusCode::NotFound)))
     }
 
-    pub fn server_error() -> Response<'a> {
+    pub fn server_error(reason: &str) -> Response<'a> {
+        warn_!("internal server error: {}", reason);
         Response(Box::new(Empty::new(StatusCode::InternalServerError)))
     }
+
+    pub fn bad_request(reason: &str) -> Response<'a> {
+        warn_!("bad request from user: {}", reason);
+        Response(Box::new(Empty::new(StatusCode::BadRequest)))
+    }
 }
 
 impl<'a> Deref for Response<'a> {