server.ts: restrict SSR to paths in the sitemap

Because Angular SSR is not very efficient, after discussion with
the Google Scholar team we realized a compromise would be to only
use SSR for pages in the DSpace sitemap.

server.ts

@@ -72,6 +72,16 @@ const cookieParser = require('cookie-parser');
 
 const appConfig: AppConfig = buildAppConfig(join(DIST_FOLDER, 'assets/config.json'));
 
+// only enable SSR for paths in the sitemap
+const SSR_PATHS = [
+  '/items/',
+  '/entities/',
+  '/collections/',
+  '/communities/',
+  '/bitstream/',
+  '/bitstreams/'
+];
+
 // cache of SSR pages for known bots, only enabled in production mode
 let botCache: LRU<string, any>;
 
@@ -218,7 +228,7 @@ export function app() {
  * The callback function to serve server side angular
  */
 function ngApp(req, res, next) {
-  if (environment.ssr.enabled) {
+  if (environment.ssr.enabled && req.method === 'GET' && SSR_PATHS.some(p => req.url.includes(p))) {
     // Render the page to user via SSR (server side rendering)
     serverSideRender(req, res, next);
   } else {