improved error message to address issue #2941 (#2955)

improved error message for missing query string in GET request, to
address issue #2941
Fixes #2941

Co-authored-by: Jesse Rosenberger <git@jro.cc>

Author: kushal-93

.changesets/fix_dev-error-message.md

@@ -0,0 +1,7 @@
+### Improved messaging when a request is received without an operation ([Issue #2941](https://github.com/apollographql/router/issues/2941))
+
+The message that is displayed when a request has been sent to the Router without an operation has been improved.  This materializes as a developer experience improvement since users (especially those using GraphqL for the first time) might send a request to the Router using a tool that isn't GraphQL-aware, or might just have their API tool of choice misconfigured.
+
+Previously, the message stated "missing query string", but now more helpfully suggests sending either a POST or GET request and specifying the desired operation as the `query` parameter (i.e., either in the POST data or in the query string parameters for GET queries).
+
+By [@kushal-93](https://github.com/kushal-93) in https://github.com/apollographql/router/pull/2955

apollo-router/src/services/router_service.rs

@@ -196,7 +196,7 @@ where
                         })
                     })
                     .unwrap_or_else(|| {
-                        Err(("missing query string", "missing query string".to_string()))
+                        Err(("There was no GraphQL operation to execute. Use the `query` parameter to send an operation, using either GET or POST.", "There was no GraphQL operation to execute. Use the `query` parameter to send an operation, using either GET or POST.".to_string()))
                     })
             } else {
                 hyper::body::to_bytes(body)