1 files changed, 29 insertions, 0 deletions
diff --git a/app/assets/javascripts/lib/apollo/instrumentation_link.js b/app/assets/javascripts/lib/apollo/instrumentation_link.js
new file mode 100644
index 00000000000..2ab364557b8
--- /dev/null
+++ b/app/assets/javascripts/lib/apollo/instrumentation_link.js
@@ -0,0 +1,29 @@
+import { ApolloLink } from 'apollo-link';
+import { memoize } from 'lodash';
+
+export const FEATURE_CATEGORY_HEADER = 'x-gitlab-feature-category';
+
+/**
+ * Returns the ApolloLink (or null) used to add instrumentation metadata to the GraphQL request.
+ *
+ * - The result will be null if the `feature_category` cannot be found.
+ * - The result is memoized since the `feature_category` is the same for the entire page.
+ */
+export const getInstrumentationLink = memoize(() => {
+  const { feature_category: featureCategory } = gon;
+
+  if (!featureCategory) {
+    return null;
+  }
+
+  return new ApolloLink((operation, forward) => {
+    operation.setContext(({ headers = {} }) => ({
+      headers: {
+        ...headers,
+        [FEATURE_CATEGORY_HEADER]: featureCategory,
+      },
+    }));
+
+    return forward(operation);
+  });
+});