events-backend: add hub http subscription API + listen by subscription ID

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

plugins/events-backend/dev/index.ts

@@ -79,6 +79,39 @@ backend.add(
               onBehalfOf: await auth.getOwnServiceCredentials(),
               targetPluginId: 'events',
             });
+
+            const subRes = await fetch(`${baseUrl}/hub/subscriptions/123`, {
+              method: 'PUT',
+              headers: {
+                Authorization: `Bearer ${token}`,
+                'Content-Type': 'application/json',
+              },
+              body: JSON.stringify({
+                topics: ['test'],
+              }),
+            });
+            console.log(
+              `DEBUG: sub create req = ${subRes.status} ${subRes.statusText}`,
+            );
+
+            const poll = async () => {
+              const res = await fetch(`${baseUrl}/hub/subscriptions/123`, {
+                headers: {
+                  Authorization: `Bearer ${token}`,
+                  'Content-Type': 'application/json',
+                },
+              });
+
+              const data = res.status === 200 && (await res.json());
+              console.log(
+                `DEBUG: sub poll req = ${res.status} ${res.statusText}`,
+                data,
+              );
+              poll();
+            };
+
+            poll();
+
             const ws = new WebSocket(`${baseUrl}/hub/connect`, {
               headers: {
                 Authorization: `Bearer ${token}`,
@@ -86,14 +119,14 @@ backend.add(
             });
             ws.onopen = () => {
               console.log('DEBUG: ws.onopen');
-              ws.send(
-                JSON.stringify([
-                  'req',
-                  1,
-                  'subscribe',
-                  { id: 'derp', topics: ['test'] },
-                ]),
-              );
+              // ws.send(
+              //   JSON.stringify([
+              //     'req',
+              //     1,
+              //     'subscribe',
+              //     { id: 'derp', topics: ['test'] },
+              //   ]),
+              // );
               setTimeout(() => {
                 console.log(`DEBUG: publish!`);
                 ws.send(

plugins/events-backend/src/service/hub/EventHub.ts

@@ -20,7 +20,7 @@ import {
   HttpAuthService,
   LoggerService,
 } from '@backstage/backend-plugin-api';
-import { Handler } from 'express';
+import express, { Handler } from 'express';
 import Router from 'express-promise-router';
 import { Socket } from 'net';
 import { STATUS_CODES } from 'http';
@@ -113,7 +113,7 @@ type EventHubStore = {
   readSubscription(id: string): Promise<{ events: EventParams[] }>;
 
   listen(
-    topicIds: string[],
+    subscriptionId: string,
     onNotify: (topicId: string) => void,
   ): Promise<() => void>;
 };
@@ -191,10 +191,14 @@ class MemoryEventHubStore implements EventHubStore {
   }
 
   async listen(
-    topicIds: string[],
+    subscriptionId: string,
     onNotify: (topicId: string) => void,
   ): Promise<() => void> {
-    const listener = { topics: new Set(topicIds), notify: onNotify };
+    const sub = this.#subscribers.get(subscriptionId);
+    if (!sub) {
+      throw new Error(`Subscription not found`);
+    }
+    const listener = { topics: sub.topics, notify: onNotify };
     this.#listeners.add(listener);
     return () => {
       this.#listeners.delete(listener);
@@ -390,8 +394,15 @@ export class EventHub {
 
     const hub = new EventHub(server, router, logger, httpAuth);
 
+    // WS
     router.get('/connect', hub.#handleGetConnect);
 
+    router.use(express.json());
+
+    // Long-polling
+    router.get('/subscriptions/:id', hub.#handleGetSubscription);
+    router.put('/subscriptions/:id', hub.#handlePutSubscription);
+
     return hub;
   }
 
@@ -474,10 +485,7 @@ export class EventHub {
                   },
                 );
 
-              const removeListener = await this.#store.listen(
-                params.topics,
-                read,
-              );
+              const removeListener = await this.#store.listen(params.id, read);
               ws.addListener('close', removeListener);
 
               await read();
@@ -518,6 +526,45 @@ export class EventHub {
     }
   };
 
+  #handleGetSubscription: Handler = async (req, res) => {
+    const credentials = await this.#httpAuth.credentials(req, {
+      allow: ['service'],
+    });
+    const id = req.params.id;
+
+    const { events } = await this.#store.readSubscription(id);
+
+    this.#logger.info(
+      `Reading subscription '${id}' resulted in ${events.length} events`,
+      { subject: credentials.principal.subject },
+    );
+
+    if (events.length > 0) {
+      res.json({ events });
+      return;
+    }
+
+    this.#store.listen(id, () => {
+      res.status(204).end();
+    });
+  };
+
+  #handlePutSubscription: Handler = async (req, res) => {
+    const credentials = await this.#httpAuth.credentials(req, {
+      allow: ['service'],
+    });
+    const id = req.params.id;
+
+    await this.#store.upsertSubscription(id, req.body.topics);
+
+    this.#logger.info(
+      `New subscription '${id}' topics='${req.body.topics.join("', '")}'`,
+      { subject: credentials.principal.subject },
+    );
+
+    res.status(201).end();
+  };
+
   close() {
     this.#connections.forEach(conn => conn.close());
     this.#connections.clear();