fix: send SSE keep-alive comment frames from Streamable HTTP server transport (v1.x) (#2538)
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Matt
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1 changed files with 252 additions and 0 deletions
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@ -3272,3 +3272,179 @@ describe('WebStandardStreamableHTTPServerTransport - onerror callback', () => {
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await storeTransport.close();
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});
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});
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describe('WebStandardStreamableHTTPServerTransport SSE keep-alive', () => {
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/** Shorthand to build a Web Standard Request for direct transport testing. */
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function req(method: string, opts?: { body?: unknown; headers?: Record<string, string> }): Request {
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const headers: Record<string, string> = { ...opts?.headers };
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if (method === 'POST') {
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headers['Accept'] ??= 'application/json, text/event-stream';
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headers['Content-Type'] ??= 'application/json';
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} else if (method === 'GET') {
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headers['Accept'] ??= 'text/event-stream';
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}
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return new Request('http://localhost/mcp', {
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method,
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headers,
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body: opts?.body !== undefined ? JSON.stringify(opts.body) : undefined
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});
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}
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async function createTransport(options?: { keepAliveMs?: number }): Promise<{
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transport: WebStandardStreamableHTTPServerTransport;
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sessionId: string;
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}> {
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const transport = new WebStandardStreamableHTTPServerTransport({ sessionIdGenerator: () => randomUUID(), ...options });
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await new McpServer({ name: 'test-server', version: '1.0.0' }).connect(transport);
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const initResponse = await transport.handleRequest(req('POST', { body: TEST_MESSAGES.initialize }));
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expect(initResponse.status).toBe(200);
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return { transport, sessionId: initResponse.headers.get('mcp-session-id') as string };
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}
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beforeEach(() => {
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vi.useFakeTimers();
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});
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afterEach(() => {
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vi.useRealTimers();
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});
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it('should write keep-alive comment frames to an idle standalone GET stream', async () => {
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const { transport, sessionId } = await createTransport();
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const response = await transport.handleRequest(
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req('GET', { headers: { 'mcp-session-id': sessionId, 'mcp-protocol-version': '2025-11-25' } })
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);
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expect(response.status).toBe(200);
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const reader = response.body!.getReader();
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await vi.advanceTimersByTimeAsync(15000);
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const { value } = await reader.read();
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expect(new TextDecoder().decode(value)).toBe(': keepalive\n\n');
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await transport.close();
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});
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it('should honor a custom keepAliveMs interval', async () => {
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const { transport, sessionId } = await createTransport({ keepAliveMs: 1000 });
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const response = await transport.handleRequest(
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req('GET', { headers: { 'mcp-session-id': sessionId, 'mcp-protocol-version': '2025-11-25' } })
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);
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const reader = response.body!.getReader();
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await vi.advanceTimersByTimeAsync(3000);
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let received = '';
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for (let i = 0; i < 3; i++) {
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const { value } = await reader.read();
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received += new TextDecoder().decode(value);
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}
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expect(received).toBe(': keepalive\n\n'.repeat(3));
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await transport.close();
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});
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it('should not write keep-alive frames when keepAliveMs is 0', async () => {
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const { transport, sessionId } = await createTransport({ keepAliveMs: 0 });
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const response = await transport.handleRequest(
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req('GET', { headers: { 'mcp-session-id': sessionId, 'mcp-protocol-version': '2025-11-25' } })
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);
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const reader = response.body!.getReader();
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await vi.advanceTimersByTimeAsync(60000);
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const read = reader.read();
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const raced = await Promise.race([read, Promise.resolve('pending')]);
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expect(raced).toBe('pending');
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await transport.close();
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});
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it('should stop keep-alive frames after the stream is closed', async () => {
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const { transport, sessionId } = await createTransport();
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const response = await transport.handleRequest(
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req('GET', { headers: { 'mcp-session-id': sessionId, 'mcp-protocol-version': '2025-11-25' } })
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);
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const reader = response.body!.getReader();
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await transport.close();
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const { done } = await reader.read();
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expect(done).toBe(true);
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// Advancing time after close must not throw or fire further writes
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expect(vi.getTimerCount()).toBe(0);
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await vi.advanceTimersByTimeAsync(60000);
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});
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it('should write keep-alive frames on a POST SSE stream while a request is pending', async () => {
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const transport = new WebStandardStreamableHTTPServerTransport({ sessionIdGenerator: () => randomUUID() });
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const mcpServer = new McpServer({ name: 'test-server', version: '1.0.0' });
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let resolveTool: (() => void) | undefined;
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mcpServer.tool('slow', async () => {
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await new Promise<void>(resolve => {
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resolveTool = resolve;
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});
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return { content: [{ type: 'text', text: 'done' }] };
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});
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await mcpServer.connect(transport);
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const initResponse = await transport.handleRequest(req('POST', { body: TEST_MESSAGES.initialize }));
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const sessionId = initResponse.headers.get('mcp-session-id') as string;
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const response = await transport.handleRequest(
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req('POST', {
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body: { jsonrpc: '2.0', method: 'tools/call', params: { name: 'slow', arguments: {} }, id: 'call-1' },
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headers: { 'mcp-session-id': sessionId, 'mcp-protocol-version': '2025-11-25' }
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})
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);
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expect(response.status).toBe(200);
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const reader = response.body!.getReader();
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await vi.advanceTimersByTimeAsync(15000);
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const { value } = await reader.read();
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expect(new TextDecoder().decode(value)).toBe(': keepalive\n\n');
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resolveTool?.();
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await transport.close();
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});
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it('should supersede the previous keep-alive timer when a replayed stream re-registers under the same stream id', async () => {
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// Event store WITHOUT the optional getStreamIdForEventId — the replay
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// path then skips its 409 conflict check, so a reconnect re-registers
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// the same stream id. The predecessor's timer must be replaced, not
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// orphaned (an orphaned timer's failing write would clear the live
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// stream's keep-alive via stopKeepAlive on the shared stream id).
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const eventStore: EventStore = {
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async storeEvent(): Promise<EventId> {
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return 'evt-1';
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},
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async replayEventsAfter(): Promise<StreamId> {
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return 'stream-1';
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}
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};
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const transport = new WebStandardStreamableHTTPServerTransport({ sessionIdGenerator: () => randomUUID(), eventStore });
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await new McpServer({ name: 'test-server', version: '1.0.0' }).connect(transport);
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const initResponse = await transport.handleRequest(req('POST', { body: TEST_MESSAGES.initialize }));
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const sessionId = initResponse.headers.get('mcp-session-id') as string;
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const replayHeaders = { 'mcp-session-id': sessionId, 'mcp-protocol-version': '2025-11-25', 'Last-Event-ID': 'evt-1' };
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const first = await transport.handleRequest(req('GET', { headers: replayHeaders }));
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expect(first.status).toBe(200);
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// Reconnect with the same Last-Event-ID — re-registers 'stream-1'
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const second = await transport.handleRequest(req('GET', { headers: replayHeaders }));
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expect(second.status).toBe(200);
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// Exactly one keep-alive timer must remain armed (plus none orphaned)
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expect(vi.getTimerCount()).toBe(1);
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// The live (second) stream still receives keep-alive frames
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const reader = second.body!.getReader();
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await vi.advanceTimersByTimeAsync(15000);
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const { value } = await reader.read();
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expect(new TextDecoder().decode(value)).toBe(': keepalive\n\n');
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await transport.close();
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});
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});
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