ext-apps/src/app-bridge.test.ts

import { describe, it, expect, beforeEach, afterEach } from "bun:test";
import { InMemoryTransport } from "@modelcontextprotocol/sdk/inMemory.js";
import type { Client } from "@modelcontextprotocol/sdk/client/index.js";
import type { ServerCapabilities } from "@modelcontextprotocol/sdk/types.js";
import { EmptyResultSchema } from "@modelcontextprotocol/sdk/types.js";

import { App } from "./app";
import { AppBridge, type McpUiHostCapabilities } from "./app-bridge";

/** Wait for pending microtasks to complete */
const flush = () => new Promise((resolve) => setTimeout(resolve, 0));

/**
 * Create a minimal mock MCP client for testing AppBridge.
 * Only implements methods that AppBridge calls.
 */
function createMockClient(
  serverCapabilities: ServerCapabilities = {},
): Pick<Client, "getServerCapabilities" | "request" | "notification"> {
  return {
    getServerCapabilities: () => serverCapabilities,
    request: async () => ({}) as never,
    notification: async () => {},
  };
}

const testHostInfo = { name: "TestHost", version: "1.0.0" };
const testAppInfo = { name: "TestApp", version: "1.0.0" };
const testHostCapabilities: McpUiHostCapabilities = {
  openLinks: {},
  serverTools: {},
  logging: {},
};

describe("App <-> AppBridge integration", () => {
  let app: App;
  let bridge: AppBridge;
  let appTransport: InMemoryTransport;
  let bridgeTransport: InMemoryTransport;

  beforeEach(() => {
    [appTransport, bridgeTransport] = InMemoryTransport.createLinkedPair();
    app = new App(testAppInfo, {}, { autoResize: false });
    bridge = new AppBridge(
      createMockClient() as Client,
      testHostInfo,
      testHostCapabilities,
    );
  });

  afterEach(async () => {
    await appTransport.close();
    await bridgeTransport.close();
  });

  describe("initialization handshake", () => {
    it("App.connect() triggers bridge.oninitialized", async () => {
      let initializedFired = false;

      bridge.oninitialized = () => {
        initializedFired = true;
      };

      await bridge.connect(bridgeTransport);
      await app.connect(appTransport);

      expect(initializedFired).toBe(true);
    });

    it("App receives host info and capabilities after connect", async () => {
      await bridge.connect(bridgeTransport);
      await app.connect(appTransport);

      const hostInfo = app.getHostVersion();
      expect(hostInfo).toEqual(testHostInfo);

      const hostCaps = app.getHostCapabilities();
      expect(hostCaps).toEqual(testHostCapabilities);
    });

    it("Bridge receives app info and capabilities after initialization", async () => {
      const appCapabilities = { tools: { listChanged: true } };
      app = new App(testAppInfo, appCapabilities, { autoResize: false });

      await bridge.connect(bridgeTransport);
      await app.connect(appTransport);

      const appInfo = bridge.getAppVersion();
      expect(appInfo).toEqual(testAppInfo);

      const appCaps = bridge.getAppCapabilities();
      expect(appCaps).toEqual(appCapabilities);
    });
  });

  describe("Host -> App notifications", () => {
    beforeEach(async () => {
      await bridge.connect(bridgeTransport);
    });

    it("sendToolInput triggers app.ontoolinput", async () => {
      const receivedArgs: unknown[] = [];
      app.ontoolinput = (params) => {
        receivedArgs.push(params.arguments);
      };

      await app.connect(appTransport);
      await bridge.sendToolInput({ arguments: { location: "NYC" } });

      expect(receivedArgs).toEqual([{ location: "NYC" }]);
    });

    it("sendToolInputPartial triggers app.ontoolinputpartial", async () => {
      const receivedArgs: unknown[] = [];
      app.ontoolinputpartial = (params) => {
        receivedArgs.push(params.arguments);
      };

      await app.connect(appTransport);
      await bridge.sendToolInputPartial({ arguments: { loc: "N" } });
      await bridge.sendToolInputPartial({ arguments: { location: "NYC" } });

      expect(receivedArgs).toEqual([{ loc: "N" }, { location: "NYC" }]);
    });

    it("sendToolResult triggers app.ontoolresult", async () => {
      const receivedResults: unknown[] = [];
      app.ontoolresult = (params) => {
        receivedResults.push(params);
      };

      await app.connect(appTransport);
      await bridge.sendToolResult({
        content: [{ type: "text", text: "Weather: Sunny" }],
      });

      expect(receivedResults).toHaveLength(1);
      expect(receivedResults[0]).toEqual({
        content: [{ type: "text", text: "Weather: Sunny" }],
      });
    });

    it("setHostContext triggers app.onhostcontextchanged", async () => {
      const receivedContexts: unknown[] = [];
      app.onhostcontextchanged = (params) => {
        receivedContexts.push(params);
      };

      await app.connect(appTransport);
      bridge.setHostContext({ theme: "dark" });
      await flush();

      expect(receivedContexts).toEqual([{ theme: "dark" }]);
    });

    it("setHostContext only sends changed values", async () => {
      const receivedContexts: unknown[] = [];
      app.onhostcontextchanged = (params) => {
        receivedContexts.push(params);
      };

      await app.connect(appTransport);

      bridge.setHostContext({ theme: "dark", locale: "en-US" });
      await flush();
      bridge.setHostContext({ theme: "dark", locale: "en-US" }); // No change
      await flush();
      bridge.setHostContext({ theme: "light", locale: "en-US" }); // Only theme changed
      await flush();

      expect(receivedContexts).toEqual([
        { theme: "dark", locale: "en-US" },
        { theme: "light" },
      ]);
    });
  });

  describe("App -> Host notifications", () => {
    beforeEach(async () => {
      await bridge.connect(bridgeTransport);
    });

    it("app.sendSizeChange triggers bridge.onsizechange", async () => {
      const receivedSizes: unknown[] = [];
      bridge.onsizechange = (params) => {
        receivedSizes.push(params);
      };

      await app.connect(appTransport);
      await app.sendSizeChange({ width: 400, height: 600 });

      expect(receivedSizes).toEqual([{ width: 400, height: 600 }]);
    });

    it("app.sendLog triggers bridge.onloggingmessage", async () => {
      const receivedLogs: unknown[] = [];
      bridge.onloggingmessage = (params) => {
        receivedLogs.push(params);
      };

      await app.connect(appTransport);
      await app.sendLog({
        level: "info",
        data: "Test log message",
        logger: "TestApp",
      });

      expect(receivedLogs).toHaveLength(1);
      expect(receivedLogs[0]).toMatchObject({
        level: "info",
        data: "Test log message",
        logger: "TestApp",
      });
    });
  });

  describe("App -> Host requests", () => {
    beforeEach(async () => {
      await bridge.connect(bridgeTransport);
    });

    it("app.sendMessage triggers bridge.onmessage and returns result", async () => {
      const receivedMessages: unknown[] = [];
      bridge.onmessage = async (params) => {
        receivedMessages.push(params);
        return {};
      };

      await app.connect(appTransport);
      const result = await app.sendMessage({
        role: "user",
        content: [{ type: "text", text: "Hello from app" }],
      });

      expect(receivedMessages).toHaveLength(1);
      expect(receivedMessages[0]).toMatchObject({
        role: "user",
        content: [{ type: "text", text: "Hello from app" }],
      });
      expect(result).toEqual({});
    });

    it("app.sendMessage returns error result when handler indicates error", async () => {
      bridge.onmessage = async () => {
        return { isError: true };
      };

      await app.connect(appTransport);
      const result = await app.sendMessage({
        role: "user",
        content: [{ type: "text", text: "Test" }],
      });

      expect(result.isError).toBe(true);
    });

    it("app.sendOpenLink triggers bridge.onopenlink and returns result", async () => {
      const receivedLinks: string[] = [];
      bridge.onopenlink = async (params) => {
        receivedLinks.push(params.url);
        return {};
      };

      await app.connect(appTransport);
      const result = await app.sendOpenLink({ url: "https://example.com" });

      expect(receivedLinks).toEqual(["https://example.com"]);
      expect(result).toEqual({});
    });

    it("app.sendOpenLink returns error when host denies", async () => {
      bridge.onopenlink = async () => {
        return { isError: true };
      };

      await app.connect(appTransport);
      const result = await app.sendOpenLink({ url: "https://blocked.com" });

      expect(result.isError).toBe(true);
    });
  });

  describe("ping", () => {
    it("App responds to ping from bridge", async () => {
      await bridge.connect(bridgeTransport);
      await app.connect(appTransport);

      // Bridge can send ping via the protocol's request method
      const result = await bridge.request(
        { method: "ping", params: {} },
        EmptyResultSchema,
      );

      expect(result).toEqual({});
    });
  });
});