[web] add includeReferer flag to SplitTestHandler.getAssignment (#33235)

* [web] add includeReferer flag to SplitTestHandler.getAssignment

* [web] tests: migrate User.getSplitTestAssignment to async/await

I don't want to fight with callbacks and optional arguments. Just move
it to async/await. New tests should use async/await, so there is no
point in making this work in callback-hell.

* [web] remove unused URL import

GitOrigin-RevId: 6251001e6ba7354f704fa663be8ef365ca0b9d23

services/web/app/src/Features/Compile/CompileController.mjs

@@ -1,4 +1,3 @@
-import { URL } from 'node:url'
 import { pipeline } from 'node:stream/promises'
 import Metrics from '@overleaf/metrics'
 import ProjectGetter from '../Project/ProjectGetter.mjs'
@@ -46,23 +45,12 @@ function getOutputFilesArchiveSpecification(projectId, userId, buildId) {
   }
 }
 
-function getPdfCachingMinChunkSize(req, res) {
-  return Settings.pdfCachingMinChunkSize
-}
-
 async function _getSplitTestOptions(req, res) {
-  // Use the query flags from the editor request for overriding the split test.
-  let query = {}
-  try {
-    const u = new URL(req.headers.referer || req.url, Settings.siteUrl)
-    query = Object.fromEntries(u.searchParams.entries())
-  } catch (e) {}
-  const editorReq = { ...req, query }
-
   const { variant } = await SplitTestHandler.promises.getAssignment(
-    editorReq,
+    req,
     res,
-    'compile-from-history'
+    'compile-from-history',
+    { includeReferer: true }
   )
   const compileFromHistory = variant === 'enabled'
 
@@ -78,7 +66,7 @@ async function _getSplitTestOptions(req, res) {
     }
   }
 
-  const pdfCachingMinChunkSize = getPdfCachingMinChunkSize(editorReq, res)
+  const pdfCachingMinChunkSize = Settings.pdfCachingMinChunkSize
   return {
     compileFromHistory,
     pdfDownloadDomain,

services/web/app/src/Features/SplitTests/SplitTestHandler.mjs

@@ -47,11 +47,17 @@ const DEFAULT_ASSIGNMENT = {
  * @param req the request
  * @param res the Express response object
  * @param splitTestName the unique name of the split test
- * @param options {Object<sync: boolean>} - for test purposes only, to force the synchronous update of the user's profile
+ * @param {Object} options
+ * @param {boolean} options.sync - for test purposes only, to force the synchronous update of the user's profile
+ * @param {boolean} options.includeReferer For ajax requests and downloads include the split test overrides of the page
  * @returns {Promise<Assignment>}
  */
-async function getAssignment(req, res, splitTestName, { sync = false } = {}) {
-  const query = req.query || {}
+async function getAssignment(
+  req,
+  res,
+  splitTestName,
+  { sync = false, includeReferer = false } = {}
+) {
   let assignment
 
   try {
@@ -60,6 +66,20 @@ async function getAssignment(req, res, splitTestName, { sync = false } = {}) {
     } else {
       await _loadSplitTestInfoInLocals(res.locals, splitTestName, req.session)
 
+      let query = req.query || {}
+      if (includeReferer && req.headers.referer) {
+        // Pick up the query of the top-level page, i.e. what's in the browsers address bar, from ajax requests.
+        // E.g. /project/:id?split-test=foo -> ajax /project/:id/compile should see split-test=foo.
+        // E.g. /project/:id?split-test=foo -> redirect /project/:id/download/zip should see split-test=foo.
+        try {
+          const u = new URL(req.headers.referer, Settings.siteUrl)
+          query = {
+            ...Object.fromEntries(u.searchParams.entries()),
+            ...query,
+          }
+        } catch {}
+      }
+
       // Check the query string for an override, ignoring an invalid value
       const queryVariant = query[splitTestName]
       if (queryVariant) {