Update schema.rs

src/schema.rs

@@ -11,6 +11,7 @@ use crate::{
     Environment, Error, ObjectType, Pos, QueryError, QueryResponse, Result, SubscriptionStream,
     SubscriptionType, Type, Variables,
 };
+use async_graphql_parser::query::OperationType;
 use bytes::Bytes;
 use futures::channel::mpsc;
 use futures::Stream;
@@ -255,6 +256,10 @@ where
             };
         }
 
+        if document.current_operation().ty != OperationType::Subscription {
+            return Err(QueryError::NotSupported.into_error(Pos::default()));
+        }
+
         let resolve_id = AtomicUsize::default();
         let environment = Arc::new(Environment {
             variables,