Initialisation

Added the packages and files for the backend server

node_modules/graphql/validation/rules/SingleFieldSubscriptionsRule.mjs

@@ -0,0 +1,77 @@
+import { GraphQLError } from '../../error/GraphQLError.mjs';
+import { Kind } from '../../language/kinds.mjs';
+import { collectFields } from '../../execution/collectFields.mjs';
+
+/**
+ * Subscriptions must only include a non-introspection field.
+ *
+ * A GraphQL subscription is valid only if it contains a single root field and
+ * that root field is not an introspection field.
+ *
+ * See https://spec.graphql.org/draft/#sec-Single-root-field
+ */
+export function SingleFieldSubscriptionsRule(context) {
+  return {
+    OperationDefinition(node) {
+      if (node.operation === 'subscription') {
+        const schema = context.getSchema();
+        const subscriptionType = schema.getSubscriptionType();
+
+        if (subscriptionType) {
+          const operationName = node.name ? node.name.value : null;
+          const variableValues = Object.create(null);
+          const document = context.getDocument();
+          const fragments = Object.create(null);
+
+          for (const definition of document.definitions) {
+            if (definition.kind === Kind.FRAGMENT_DEFINITION) {
+              fragments[definition.name.value] = definition;
+            }
+          }
+
+          const fields = collectFields(
+            schema,
+            fragments,
+            variableValues,
+            subscriptionType,
+            node.selectionSet,
+          );
+
+          if (fields.size > 1) {
+            const fieldSelectionLists = [...fields.values()];
+            const extraFieldSelectionLists = fieldSelectionLists.slice(1);
+            const extraFieldSelections = extraFieldSelectionLists.flat();
+            context.reportError(
+              new GraphQLError(
+                operationName != null
+                  ? `Subscription "${operationName}" must select only one top level field.`
+                  : 'Anonymous Subscription must select only one top level field.',
+                {
+                  nodes: extraFieldSelections,
+                },
+              ),
+            );
+          }
+
+          for (const fieldNodes of fields.values()) {
+            const field = fieldNodes[0];
+            const fieldName = field.name.value;
+
+            if (fieldName.startsWith('__')) {
+              context.reportError(
+                new GraphQLError(
+                  operationName != null
+                    ? `Subscription "${operationName}" must not select an introspection top level field.`
+                    : 'Anonymous Subscription must not select an introspection top level field.',
+                  {
+                    nodes: fieldNodes,
+                  },
+                ),
+              );
+            }
+          }
+        }
+      }
+    },
+  };
+}