Add endpoint for the Dev UI to subscribe to runtime updates

genkit-tools/common/src/manager/manager.ts

@@ -16,9 +16,9 @@
 
 import axios, { AxiosError } from 'axios';
 import chokidar from 'chokidar';
+import EventEmitter from 'events';
 import fs from 'fs/promises';
 import path from 'path';
-
 import {
   Action,
   RunActionResponse,
@@ -28,18 +28,12 @@ import * as apis from '../types/apis';
 import { TraceData } from '../types/trace';
 import { logger } from '../utils/logger';
 import { checkServerHealth, findRuntimesDir } from '../utils/utils';
-import { GenkitToolsError, StreamingCallback } from './types';
-
-interface RuntimeInfo {
-  /** Runtime ID (either user-set or `pid`). */
-  id: string;
-  /** Process ID of the runtime. */
-  pid: number;
-  /** URL of the reflection server. */
-  reflectionServerUrl: string;
-  /** Timestamp when the runtime was started. */
-  timestamp: string;
-}
+import {
+  GenkitToolsError,
+  RuntimeEvent,
+  RuntimeInfo,
+  StreamingCallback,
+} from './types';
 
 const STREAM_DELIMITER = '\n';
 const HEALTH_CHECK_INTERVAL = 5000;
@@ -54,6 +48,7 @@ interface RuntimeManagerOptions {
 export class RuntimeManager {
   private filenameToRuntimeMap: Record<string, RuntimeInfo> = {};
   private idToFileMap: Record<string, string> = {};
+  private eventEmitter = new EventEmitter();
 
   private constructor(
     readonly telemetryServerUrl?: string,
@@ -110,6 +105,23 @@ export class RuntimeManager {
         );
   }
 
+  /**
+   * Subscribe to changes to the available runtimes. e.g.) whenever a new
+   * runtime is added or removed.
+   *
+   * The `listener` will be called with the `eventType` that occured and the
+   * `runtime` to which it applies.
+   *
+   * @param listener the callback function.
+   */
+  onRuntimeEvent(
+    listener: (eventType: RuntimeEvent, runtime: RuntimeInfo) => void
+  ) {
+    Object.values(RuntimeEvent).forEach((event) =>
+      this.eventEmitter.on(event, (rt) => listener(event, rt))
+    );
+  }
+
   /**
    * Retrieves all runnable actions.
    */
@@ -305,6 +317,7 @@ export class RuntimeManager {
         if (await checkServerHealth(runtimeInfo.reflectionServerUrl)) {
           this.filenameToRuntimeMap[fileName] = runtimeInfo;
           this.idToFileMap[runtimeInfo.id] = fileName;
+          this.eventEmitter.emit(RuntimeEvent.ADD, runtimeInfo);
           await this.notifyRuntime(runtimeInfo);
           logger.debug(
             `Added runtime with ID ${runtimeInfo.id} at URL: ${runtimeInfo.reflectionServerUrl}`
@@ -326,10 +339,11 @@ export class RuntimeManager {
   private handleRemovedRuntime(filePath: string) {
     const fileName = path.basename(filePath);
     if (fileName in this.filenameToRuntimeMap) {
-      const id = this.filenameToRuntimeMap[fileName].id;
+      const runtime = this.filenameToRuntimeMap[fileName];
       delete this.filenameToRuntimeMap[fileName];
-      delete this.idToFileMap[id];
-      logger.debug(`Removed runtime with id ${id}.`);
+      delete this.idToFileMap[runtime.id];
+      this.eventEmitter.emit(RuntimeEvent.REMOVE, runtime);
+      logger.debug(`Removed runtime with id ${runtime.id}.`);
     }
   }
 

genkit-tools/common/src/manager/types.ts

@@ -26,3 +26,19 @@ export class GenkitToolsError extends Error {
 
 // Streaming callback function.
 export type StreamingCallback<T> = (chunk: T) => void;
+
+export interface RuntimeInfo {
+  /** Runtime ID (either user-set or `pid`). */
+  id: string;
+  /** Process ID of the runtime. */
+  pid: number;
+  /** URL of the reflection server. */
+  reflectionServerUrl: string;
+  /** Timestamp when the runtime was started. */
+  timestamp: string;
+}
+
+export enum RuntimeEvent {
+  ADD = 'add',
+  REMOVE = 'remove',
+}

genkit-tools/common/src/server/server.ts

@@ -79,6 +79,36 @@ export async function startServer(manager: RuntimeManager, port: number) {
     res.end();
   });
 
+  // General purpose endpoint for Server Side Events to the Developer UI.
+  // Currently only event type "current-time" is supported, which notifies the
+  // subsriber of the currently selected Genkit Runtime (typically most recent).
+  app.get('/api/sse', async (_, res) => {
+    res.writeHead(200, {
+      'Access-Control-Allow-Origin': '*',
+      'Cache-Control': 'no-cache',
+      'Content-Type': 'text/event-stream',
+      Connection: 'keep-alive',
+    });
+
+    // On connection, immediately send the "current" runtime (i.e. most recent)
+    const runtimeInfo = JSON.stringify(manager.getMostRecentRuntime() ?? {});
+    res.write('event: current-runtime\n');
+    res.write(`data: ${runtimeInfo}\n\n`);
+
+    // When runtimes are added or removed, notify the Dev UI which runtime
+    // is considered "current" (i.e. most recent). In the future, we could send
+    // updates and let the developer decide which to use.
+    manager.onRuntimeEvent(() => {
+      const runtimeInfo = JSON.stringify(manager.getMostRecentRuntime() ?? {});
+      res.write('event: current-runtime\n');
+      res.write(`data: ${runtimeInfo}\n\n`);
+    });
+
+    res.on('close', () => {
+      res.end();
+    });
+  });
+
   app.get('/api/__health', (_, res) => {
     res.status(200).send('');
   });

genkit-tools/common/src/types/index.ts

@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+export { RuntimeEvent, RuntimeInfo } from '../manager/types';
 export * from './action';
 export * from './analytics';
 export * from './apis';