feat: enhance analytics input to prioritize document referrer

- Updated AnalyticsInput to include an optional document_referrer field, allowing for better tracking of the previous page.
- Modified POST request handling to prefer document_referrer over the HTTP Referer header, ensuring more accurate analytics data.
- Adjusted ResourceViewTracker to pass the document referrer correctly, maintaining a maximum length of 2048 characters.

Author: kingRayhan

src/app/api/analytics/view/route.ts

@@ -32,7 +32,11 @@ export async function POST(req: Request) {
   }
 
   const userId = await authID();
-  const referrer = req.headers.get("referer");
+
+  const referrer =
+    parsed.data.document_referrer !== undefined
+      ? parsed.data.document_referrer.trim().slice(0, 2048) || null
+      : req.headers.get("referer")?.slice(0, 2048) ?? null;
 
   const session =
     userId != null

src/backend/services/inputs/analytics.input.ts

@@ -55,6 +55,11 @@ export const AnalyticsInput = {
     resource_type: z.enum(TRACKED_RESOURCE_TYPES),
     resource_id: z.string().uuid(),
     session_id: z.string().min(8).max(128),
+    /**
+     * `document.referrer` at page load (previous page). Prefer this over the HTTP
+     * Referer on this POST, which is usually the article URL (fetch initiator).
+     */
+    document_referrer: z.union([z.string().max(2048), z.literal("")]).optional(),
   }),
 
   getResourceAnalyticsInput: z

src/components/analytics/ResourceViewTracker.tsx

@@ -46,6 +46,9 @@ export function ResourceViewTracker({
       resource_type: resourceType,
       resource_id: resourceId,
       session_id: sessionId,
+      document_referrer: document.referrer
+        ? document.referrer.slice(0, 2048)
+        : "",
     });
 
     try {