[DURACOM-344] switch to blacklist approach for SSR

Author: FrancescoMolinaro

config/config.example.yml

@@ -23,10 +23,13 @@ ssr:
   # Determining which styles are critical is a relatively expensive operation; this option is
   # disabled (false) by default to boost server performance at the expense of loading smoothness.
   inlineCriticalCss: false
-  # Path prefixes to enable SSR for. By default these are limited to paths of primary DSpace objects.
-  # NOTE: The "/handle/" path ensures Handle redirects work via SSR.  The "/reload/" path ensures
-  # hard refreshes (e.g. after login) trigger SSR while fully reloading the page.
-  paths: [ '/home', '/items/', '/entities/', '/collections/', '/communities/', '/bitstream/', '/bitstreams/', '/handle/', '/reload/' ]
+  # Path prefixes to disable SSR for. If the path the user is visiting starts with one of the excluded paths, it will be served directly in CSR.
+  # These should be limited to paths that might cause high consumption in resources (e.g. crawler on pages with many items to follow).
+  excludePaths: ['/browse/', '/community-list', '/search/', '/statistics' ]
+  # Regexes to be run against the URl of the page to check if SSR is allowed.
+  # This configuration offers more flexibility and precision than excludePaths as we can match more complex URLs.
+  # If the entire URL match any of the regexes it will be served directly in CSR.
+  ssrBlacklistRegexes: [ /^\/communities\/[0-9a-fA-F-]{36}(\/.*)?$/, /^\/collections\/[0-9a-fA-F-]{36}(\/.*)?$/]
   # Whether to enable rendering of Search component on SSR.
   # If set to true the component will be included in the HTML returned from the server side rendering.
   # If set to false the component will not be included in the HTML returned from the server side rendering.

server.ts

@@ -221,7 +221,7 @@ export function app() {
  * The callback function to serve server side angular
  */
 function ngApp(req, res, next) {
-  if (environment.ssr.enabled && req.method === 'GET' && (req.path === '/' || environment.ssr.paths.some(pathPrefix => req.path.startsWith(pathPrefix)))) {
+    if (environment.ssr.enabled && req.method === 'GET' && (req.path === '/' || !isBlacklistedPathForSsr(req.url, req.path, environment.ssr.ssrBlacklistRegexes))) {
     // Render the page to user via SSR (server side rendering)
     serverSideRender(req, res, next);
   } else {
@@ -627,6 +627,17 @@ function start() {
   }
 }
 
+/**
+ * Check if SSR should be skipped for url or path
+ *
+ * @param url
+ * @param path
+ * @param blacklist
+ */
+function isBlacklistedPathForSsr(url: string, path: string, blacklist: RegExp[]): boolean {
+  return blacklist.some((regex) => regex.test(url)) || environment.ssr.excludePaths.some(blacklistedPath => path.startsWith(blacklistedPath));
+}
+
 /*
  * The callback function to serve health check requests
  */

src/config/ssr-config.interface.ts

@@ -39,9 +39,14 @@ export interface SSRConfig extends Config {
   replaceRestUrl: boolean;
 
   /**
-   * Paths to enable SSR for. Defaults to the home page and paths in the sitemap.
+   * Paths to disable SSR for, to avoid some possible performance issue for specific pages.
    */
-  paths: Array<string>;
+  excludePaths: Array<string>;
+
+  /**
+   * Regexes to match url and check if SSR is enabled for it.
+   */
+  ssrBlacklistRegexes:  RegExp[];
 
   /**
    * Whether to enable rendering of search component on SSR

src/environments/environment.production.ts

@@ -10,7 +10,11 @@ export const environment: Partial<BuildConfig> = {
     inlineCriticalCss: false,
     transferState: true,
     replaceRestUrl: true,
-    paths: [ '/home', '/items/', '/entities/', '/collections/', '/communities/', '/bitstream/', '/bitstreams/', '/handle/', '/reload/', '/500', '/404', '/403' ],
+    excludePaths: [ '/browse/', '/community-list', '/search/', '/statistics' ],
+    ssrBlacklistRegexes: [
+      /^\/communities\/[0-9a-fA-F-]{36}(\/.*)?$/,
+      /^\/collections\/[0-9a-fA-F-]{36}(\/.*)?$/,
+    ],
     enableSearchComponent: false,
     enableBrowseComponent: false,
   },

src/environments/environment.test.ts

@@ -14,7 +14,11 @@ export const environment: BuildConfig = {
     inlineCriticalCss: false,
     transferState: true,
     replaceRestUrl: false,
-    paths: [ '/home', '/items/', '/entities/', '/collections/', '/communities/', '/bitstream/', '/bitstreams/', '/handle/', '/reload/' ],
+    excludePaths: [ '/browse/', '/community-list', '/search/', '/statistics' ],
+    ssrBlacklistRegexes: [
+      /^\/communities\/[0-9a-fA-F-]{36}(\/.*)?$/,
+      /^\/collections\/[0-9a-fA-F-]{36}(\/.*)?$/,
+    ],
     enableSearchComponent: false,
     enableBrowseComponent: false,
   },

src/environments/environment.ts

@@ -15,7 +15,11 @@ export const environment: Partial<BuildConfig> = {
     inlineCriticalCss: false,
     transferState: true,
     replaceRestUrl: false,
-    paths: [ '/home', '/items/', '/entities/', '/collections/', '/communities/', '/bitstream/', '/bitstreams/', '/handle/', '/reload/' ],
+    excludePaths: [ '/browse/', '/community-list', '/search/', '/statistics' ],
+    ssrBlacklistRegexes: [
+      /^\/communities\/[0-9a-fA-F-]{36}(\/.*)?$/,
+      /^\/collections\/[0-9a-fA-F-]{36}(\/.*)?$/,
+    ],
     enableSearchComponent: false,
     enableBrowseComponent: false,
   },