Add server-side ServerAddOn entity

Reviewed By: lblasa

Differential Revision: D33982373

fbshipit-source-id: a07589e515fe82d3735402cc26d1258e1d212931

desktop/flipper-server-core/src/plugins/ServerAddOn.tsx

@@ -0,0 +1,71 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import assert from 'assert';
+import {assertNotNull} from '../comms/Utilities';
+
+type ServerAddOnCleanup = () => Promise<void>;
+interface ServerAddOnModule {
+  serverAddOn?: () => Promise<ServerAddOnCleanup>;
+}
+
+// TODO: Fix potential race conditions when starting/stopping concurrently
+export class ServerAddOn {
+  private owners: Set<string>;
+
+  constructor(
+    public readonly path: string,
+    private readonly cleanup: ServerAddOnCleanup,
+    initialOwner: string,
+  ) {
+    this.owners = new Set(initialOwner);
+  }
+
+  static async start(path: string, initialOwner: string): Promise<ServerAddOn> {
+    console.info('ServerAddOn.start', path);
+
+    const {serverAddOn} = require(path) as ServerAddOnModule;
+    assertNotNull(serverAddOn);
+    assert(
+      typeof serverAddOn === 'function',
+      `ServerAddOn ${path} must export "serverAddOn" function.`,
+    );
+
+    const cleanup = await serverAddOn();
+    assert(
+      typeof cleanup === 'function',
+      `ServerAddOn ${path} must return a clean up function, instead it returned ${typeof cleanup}.`,
+    );
+
+    return new ServerAddOn(path, cleanup, initialOwner);
+  }
+
+  addOwner(owner: string) {
+    this.owners.add(owner);
+  }
+
+  removeOwner(owner: string) {
+    this.owners.delete(owner);
+
+    if (!this.owners.size) {
+      this.stop().catch((e) => {
+        console.error(
+          'ServerAddOn.removeOwner -> failed to stop automatically when no owners left',
+          this.path,
+          e,
+        );
+      });
+    }
+  }
+
+  private async stop() {
+    console.info('ServerAddOn.stop', this.path);
+    await this.cleanup();
+  }
+}