TechDocs: Make requestUrl and storageUrl optional configs by using discovery APIs

closes #3715

Co-authored-by: Himanshu Mishra <himanshu@orkohunter.net>

plugins/techdocs-backend/config.d.ts

@@ -24,7 +24,7 @@ export interface Config {
      * attr: 'storageUrl' - accepts a string value
      * e.g. storageUrl: http://localhost:7000/api/techdocs/static/docs
      */
-    storageUrl: string;
+    storageUrl?: string;
     /**
      * documentation building process depends on the builder attr
      * attr: 'builder' - accepts a string value

plugins/techdocs-backend/src/service/router.ts

@@ -26,7 +26,10 @@ import {
   PublisherBase,
   getLocationForEntity,
 } from '@backstage/techdocs-common';
-import { PluginEndpointDiscovery } from '@backstage/backend-common';
+import {
+  PluginEndpointDiscovery,
+  SingleHostDiscovery,
+} from '@backstage/backend-common';
 import { Entity } from '@backstage/catalog-model';
 import { getEntityNameFromUrlPath } from './helpers';
 import { DocsBuilder } from '../DocsBuilder';
@@ -102,7 +105,10 @@ export async function createRouter({
 
   router.get('/docs/:namespace/:kind/:name/*', async (req, res) => {
     const { kind, namespace, name } = req.params;
-    const storageUrl = config.getString('techdocs.storageUrl');
+    const discoveryApi = SingleHostDiscovery.fromConfig(config);
+    const storageUrl =
+      config.getOptionalString('techdocs.storageUrl') ??
+      `${await discoveryApi.getBaseUrl('techdocs')}/static/docs`;
 
     const catalogUrl = await discovery.getBaseUrl('catalog');
     const triple = [kind, namespace, name].map(encodeURIComponent).join('/');