feat(gateway): add optional bonjour/mdns discovery

src/gateway/discovery.test.ts

@@ -0,0 +1,102 @@
+import { describe, it, expect, vi, beforeAll, beforeEach } from 'vitest';
+import { spawn } from 'child_process';
+import { EventEmitter } from 'events';
+import type { ChildProcess } from 'child_process';
+
+vi.mock('child_process', () => ({
+  spawn: vi.fn(),
+}));
+
+class MockChildProcess extends EventEmitter {
+  exitCode: number | null = null;
+  killed = false;
+  unref = vi.fn();
+  kill = vi.fn((signal?: NodeJS.Signals) => {
+    this.killed = true;
+    this.emit('exit', signal === 'SIGKILL' ? 137 : 0, signal ?? null);
+    return true;
+  });
+}
+
+const mockSpawn = vi.mocked(spawn);
+
+describe('gateway discovery', () => {
+  let startGatewayDiscovery: typeof import('./discovery.js').startGatewayDiscovery;
+
+  beforeAll(async () => {
+    const mod = await import('./discovery.js');
+    startGatewayDiscovery = mod.startGatewayDiscovery;
+  });
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it('starts avahi publisher with txt records', async () => {
+    const child = new MockChildProcess();
+    mockSpawn.mockReturnValueOnce(child as unknown as ChildProcess);
+    setTimeout(() => child.emit('spawn'), 0);
+
+    const handle = await startGatewayDiscovery({
+      serviceName: 'flynn-gateway',
+      serviceType: '_flynn._tcp',
+      port: 18800,
+      txtRecord: { instance: 'pid-123', version: '0.1.0' },
+    });
+
+    expect(mockSpawn).toHaveBeenCalledWith('avahi-publish-service', [
+      'flynn-gateway',
+      '_flynn._tcp',
+      '18800',
+      'instance=pid-123',
+      'version=0.1.0',
+    ], { stdio: 'ignore' });
+    expect(child.unref).toHaveBeenCalledOnce();
+
+    await handle.stop();
+    expect(child.kill).toHaveBeenCalledWith('SIGTERM');
+  });
+
+  it('falls back to dns-sd when avahi is unavailable', async () => {
+    const avahiChild = new MockChildProcess();
+    const dnsChild = new MockChildProcess();
+    mockSpawn.mockReturnValueOnce(avahiChild as unknown as ChildProcess);
+    mockSpawn.mockReturnValueOnce(dnsChild as unknown as ChildProcess);
+
+    setTimeout(() => avahiChild.emit('error', new Error('ENOENT')), 0);
+    setTimeout(() => dnsChild.emit('spawn'), 0);
+
+    const handle = await startGatewayDiscovery({
+      serviceName: 'flynn-gateway',
+      serviceType: '_flynn._tcp',
+      port: 18800,
+    });
+
+    expect(mockSpawn).toHaveBeenNthCalledWith(2, 'dns-sd', [
+      '-R',
+      'flynn-gateway',
+      '_flynn._tcp',
+      'local',
+      '18800',
+    ], { stdio: 'ignore' });
+
+    await handle.stop();
+    expect(dnsChild.kill).toHaveBeenCalledWith('SIGTERM');
+  });
+
+  it('throws when no supported advertiser command is available', async () => {
+    const avahiChild = new MockChildProcess();
+    const dnsChild = new MockChildProcess();
+    mockSpawn.mockReturnValueOnce(avahiChild as unknown as ChildProcess);
+    mockSpawn.mockReturnValueOnce(dnsChild as unknown as ChildProcess);
+
+    setTimeout(() => avahiChild.emit('error', new Error('ENOENT')), 0);
+    setTimeout(() => dnsChild.emit('error', new Error('ENOENT')), 0);
+
+    await expect(startGatewayDiscovery({
+      serviceName: 'flynn-gateway',
+      serviceType: '_flynn._tcp',
+      port: 18800,
+    })).rejects.toThrow(/Failed to start mDNS advertiser/);
+  });
+});