feat: signals plugins

next try after #18153 without any external dependencies and only
supporting websocket. missing tests and necessary documentation but will
work on those after initial comments if this would be proper way to go
forward. already planning for the notification plugins on top of this.

Signed-off-by: Heikki Hellgren <heikki.hellgren@op.fi>

plugins/signals-node/src/SignalsService.ts

@@ -0,0 +1,226 @@
+/*
+ * Copyright 2023 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+import {
+  EventBroker,
+  EventParams,
+  EventSubscriber,
+} from '@backstage/plugin-events-node';
+import { Logger } from 'winston';
+import { ServiceOptions, SignalConnection } from './types';
+import { RawData, WebSocket, WebSocketServer } from 'ws';
+import { IncomingMessage } from 'http';
+import { v4 as uuid } from 'uuid';
+import { Request } from 'express';
+import { JsonObject } from '@backstage/types';
+import {
+  BackstageIdentityResponse,
+  IdentityApi,
+} from '@backstage/plugin-auth-node';
+
+/** @public */
+export type SignalsEventBrokerPayload = {
+  recipients?: string[];
+  topic?: string;
+  message?: JsonObject;
+};
+
+/** @public */
+export class SignalsService implements EventSubscriber {
+  private readonly serverId: string;
+  private connections: Map<string, SignalConnection> = new Map<
+    string,
+    SignalConnection
+  >();
+  private eventBroker?: EventBroker;
+  private logger: Logger;
+  private identity: IdentityApi;
+  private server: WebSocketServer;
+
+  static create(options: ServiceOptions) {
+    return new SignalsService(options);
+  }
+
+  private constructor(options: ServiceOptions) {
+    ({
+      eventBroker: this.eventBroker,
+      logger: this.logger,
+      identity: this.identity,
+    } = options);
+
+    this.serverId = uuid();
+    this.server = new WebSocketServer({
+      noServer: true,
+    });
+
+    this.server.on('close', () => {
+      this.logger.info('Closing signals server');
+      this.connections.forEach(conn => {
+        conn.ws.close();
+      });
+      this.connections = new Map();
+    });
+
+    this.eventBroker?.subscribe(this);
+  }
+
+  handleUpgrade = async (req: Request) => {
+    const identity = await this.identity.getIdentity({
+      request: req,
+    });
+
+    this.server.handleUpgrade(
+      req,
+      req.socket,
+      Buffer.from(''),
+      (ws: WebSocket, __: IncomingMessage) => {
+        this.addConnection(ws, identity);
+      },
+    );
+  };
+
+  private addConnection(ws: WebSocket, identity?: BackstageIdentityResponse) {
+    const id = uuid();
+
+    const conn = {
+      id,
+      user: identity?.identity.userEntityRef ?? 'user:default/guest',
+      ws,
+      ownershipEntityRefs: identity?.identity.ownershipEntityRefs ?? [],
+      subscriptions: new Set<string>(),
+    };
+
+    this.connections.set(id, conn);
+
+    ws.on('error', (err: Error) => {
+      this.logger.info(
+        `Error occurred with connection ${id}: ${err}, closing connection`,
+      );
+      ws.close();
+      this.connections.delete(id);
+    });
+
+    ws.on('close', (code: number, reason: Buffer) => {
+      this.logger.info(
+        `Connection ${id} closed with code ${code}, reason: ${reason}`,
+      );
+      this.connections.delete(id);
+    });
+
+    ws.on('ping', () => {
+      this.logger.debug(`Ping from connection ${id}`);
+      ws.pong();
+    });
+
+    ws.on('message', (data: RawData, isBinary: boolean) => {
+      this.logger.debug(`Received message from connection ${id}: ${data}`);
+      if (isBinary) {
+        return;
+      }
+
+      try {
+        const json = JSON.parse(data.toString()) as JsonObject;
+        this.handleMessage(conn, json);
+      } catch (err: any) {
+        this.logger.error(
+          `Invalid message received from connection ${id}: ${err}`,
+        );
+      }
+    });
+  }
+
+  private handleMessage(connection: SignalConnection, message: JsonObject) {
+    if (message.action === 'subscribe' && message.topic) {
+      this.logger.info(
+        `Connection ${connection.id} subscribed to ${message.topic}`,
+      );
+      connection.subscriptions.add(message.topic as string);
+    }
+
+    if (message.action === 'unsubscribe' && message.topic) {
+      this.logger.info(
+        `Connection ${connection.id} unsubscribed from ${message.topic}`,
+      );
+      connection.subscriptions.delete(message.topic as string);
+    }
+  }
+
+  async publish(to: string | string[], message: JsonObject, topic?: string) {
+    await this.publishInternal(
+      Array.isArray(to) ? to : [to],
+      message,
+      false,
+      topic,
+    );
+  }
+
+  private async publishInternal(
+    recipients: string[],
+    message: JsonObject,
+    brokedEvent: boolean,
+    topic?: string,
+  ) {
+    this.connections.forEach(conn => {
+      if (topic && !conn.subscriptions.has(topic)) {
+        return;
+      }
+      // Sending to all users can be done with '*'
+      if (
+        !recipients.includes('*') &&
+        !conn.ownershipEntityRefs.some(ref => recipients.includes(ref))
+      ) {
+        return;
+      }
+      conn.ws.send(JSON.stringify({ topic, message }));
+    });
+
+    // If this event has not been broadcasted to all servers, then use
+    // EventBroker to do that
+    if (this.eventBroker && !brokedEvent) {
+      await this.eventBroker.publish({
+        topic: 'signals',
+        eventPayload: {
+          recipients,
+          message,
+          topic,
+        },
+        metadata: { server: this.serverId },
+      });
+    }
+  }
+
+  async onEvent(params: EventParams<SignalsEventBrokerPayload>): Promise<void> {
+    const { eventPayload, metadata } = params;
+    // Discard message from same server to prevent duplicate messages
+    if (!metadata?.server || metadata.server === this.serverId) {
+      return;
+    }
+
+    if (!eventPayload?.recipients || !eventPayload.message) {
+      return;
+    }
+
+    await this.publishInternal(
+      eventPayload.recipients,
+      eventPayload.message,
+      true,
+      eventPayload.topic,
+    );
+  }
+
+  supportsEventTopics(): string[] {
+    return ['signals'];
+  }
+}

plugins/signals-node/src/index.ts

@@ -0,0 +1,18 @@
+/*
+ * Copyright 2023 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+export * from './SignalsService';
+export * from './types';

plugins/signals-node/src/setupTests.ts

@@ -0,0 +1,16 @@
+/*
+ * Copyright 2023 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+export {};

plugins/signals-node/src/types.ts

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2023 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+import { IdentityApi } from '@backstage/plugin-auth-node';
+import { EventBroker } from '@backstage/plugin-events-node';
+import { Logger } from 'winston';
+import { WebSocket } from 'ws';
+
+/**
+ * @public
+ */
+export type ServiceOptions = {
+  eventBroker?: EventBroker;
+  logger: Logger;
+  identity: IdentityApi;
+};
+
+/**
+ * @internal
+ */
+export type SignalConnection = {
+  id: string;
+  user: string;
+  ws: WebSocket;
+  ownershipEntityRefs: string[];
+  subscriptions: Set<string>;
+};