feat: implement SEP-1699 SSE polling via server-side disconnect (#1129)
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Felix Weinberger
GitHub
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commit
3c50d07e9f
1 changed files with 916 additions and 30 deletions
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@ -799,6 +799,70 @@ describe('StreamableHTTPClientTransport', () => {
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expect(fetchMock).toHaveBeenCalledTimes(1);
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expect(fetchMock.mock.calls[0][1]?.method).toBe('POST');
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});
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it('should reconnect a POST-initiated stream after receiving a priming event', async () => {
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// ARRANGE
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transport = new StreamableHTTPClientTransport(new URL('http://localhost:1234/mcp'), {
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reconnectionOptions: {
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initialReconnectionDelay: 10,
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maxRetries: 1,
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maxReconnectionDelay: 1000,
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reconnectionDelayGrowFactor: 1
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}
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});
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const errorSpy = vi.fn();
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transport.onerror = errorSpy;
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// Create a stream that sends a priming event (with ID) then closes
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const streamWithPrimingEvent = new ReadableStream({
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start(controller) {
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// Send a priming event with an ID - this enables reconnection
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controller.enqueue(
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new TextEncoder().encode('id: event-123\ndata: {"jsonrpc":"2.0","method":"notifications/message","params":{}}\n\n')
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);
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// Then close the stream (simulating server disconnect)
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controller.close();
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}
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});
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const fetchMock = global.fetch as Mock;
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// First call: POST returns streaming response with priming event
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fetchMock.mockResolvedValueOnce({
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ok: true,
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status: 200,
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headers: new Headers({ 'content-type': 'text/event-stream' }),
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body: streamWithPrimingEvent
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});
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// Second call: GET reconnection - return 405 to stop further reconnection
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fetchMock.mockResolvedValueOnce({
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ok: false,
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status: 405,
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headers: new Headers()
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});
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const requestMessage: JSONRPCRequest = {
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jsonrpc: '2.0',
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method: 'long_running_tool',
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id: 'request-1',
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params: {}
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};
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// ACT
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await transport.start();
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await transport.send(requestMessage);
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// Wait for stream to process and reconnection to be scheduled
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await vi.advanceTimersByTimeAsync(50);
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// ASSERT
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// THE KEY ASSERTION: Fetch was called TWICE - POST then GET reconnection
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expect(fetchMock).toHaveBeenCalledTimes(2);
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expect(fetchMock.mock.calls[0][1]?.method).toBe('POST');
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expect(fetchMock.mock.calls[1][1]?.method).toBe('GET');
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// Verify Last-Event-ID header was sent for reconnection
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const reconnectHeaders = fetchMock.mock.calls[1][1]?.headers as Headers;
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expect(reconnectHeaders.get('last-event-id')).toBe('event-123');
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});
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});
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it('invalidates all credentials on InvalidClientError during auth', async () => {
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@ -1102,6 +1166,148 @@ describe('StreamableHTTPClientTransport', () => {
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});
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});
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describe('SSE retry field handling', () => {
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beforeEach(() => {
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vi.useFakeTimers();
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(global.fetch as Mock).mockReset();
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});
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afterEach(() => vi.useRealTimers());
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it('should use server-provided retry value for reconnection delay', async () => {
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transport = new StreamableHTTPClientTransport(new URL('http://localhost:1234/mcp'), {
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reconnectionOptions: {
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initialReconnectionDelay: 100,
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maxReconnectionDelay: 5000,
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reconnectionDelayGrowFactor: 2,
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maxRetries: 3
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}
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});
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// Create a stream that sends a retry field
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const encoder = new TextEncoder();
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const stream = new ReadableStream({
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start(controller) {
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// Send SSE event with retry field
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const event =
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'retry: 3000\nevent: message\nid: evt-1\ndata: {"jsonrpc": "2.0", "method": "notification", "params": {}}\n\n';
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controller.enqueue(encoder.encode(event));
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// Close stream to trigger reconnection
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controller.close();
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}
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});
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const fetchMock = global.fetch as Mock;
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fetchMock.mockResolvedValueOnce({
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ok: true,
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status: 200,
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headers: new Headers({ 'content-type': 'text/event-stream' }),
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body: stream
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});
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// Second request for reconnection
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fetchMock.mockResolvedValueOnce({
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ok: true,
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status: 200,
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headers: new Headers({ 'content-type': 'text/event-stream' }),
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body: new ReadableStream()
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});
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await transport.start();
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await transport['_startOrAuthSse']({});
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// Wait for stream to close and reconnection to be scheduled
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await vi.advanceTimersByTimeAsync(100);
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// Verify the server retry value was captured
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const transportInternal = transport as unknown as { _serverRetryMs?: number };
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expect(transportInternal._serverRetryMs).toBe(3000);
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// Verify the delay calculation uses server retry value
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const getDelay = transport['_getNextReconnectionDelay'].bind(transport);
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expect(getDelay(0)).toBe(3000); // Should use server value, not 100ms initial
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expect(getDelay(5)).toBe(3000); // Should still use server value for any attempt
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});
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it('should fall back to exponential backoff when no server retry value', () => {
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transport = new StreamableHTTPClientTransport(new URL('http://localhost:1234/mcp'), {
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reconnectionOptions: {
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initialReconnectionDelay: 100,
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maxReconnectionDelay: 5000,
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reconnectionDelayGrowFactor: 2,
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maxRetries: 3
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}
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});
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// Without any SSE stream, _serverRetryMs should be undefined
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const transportInternal = transport as unknown as { _serverRetryMs?: number };
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expect(transportInternal._serverRetryMs).toBeUndefined();
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// Should use exponential backoff
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const getDelay = transport['_getNextReconnectionDelay'].bind(transport);
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expect(getDelay(0)).toBe(100); // 100 * 2^0
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expect(getDelay(1)).toBe(200); // 100 * 2^1
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expect(getDelay(2)).toBe(400); // 100 * 2^2
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expect(getDelay(10)).toBe(5000); // capped at max
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});
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it('should reconnect on graceful stream close', async () => {
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transport = new StreamableHTTPClientTransport(new URL('http://localhost:1234/mcp'), {
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reconnectionOptions: {
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initialReconnectionDelay: 10,
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maxReconnectionDelay: 1000,
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reconnectionDelayGrowFactor: 1,
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maxRetries: 1
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}
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});
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// Create a stream that closes gracefully after sending an event with ID
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const encoder = new TextEncoder();
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const stream = new ReadableStream({
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start(controller) {
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// Send priming event with ID and retry field
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const event = 'id: evt-1\nretry: 100\ndata: \n\n';
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controller.enqueue(encoder.encode(event));
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// Graceful close
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controller.close();
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}
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});
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const fetchMock = global.fetch as Mock;
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fetchMock.mockResolvedValueOnce({
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ok: true,
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status: 200,
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headers: new Headers({ 'content-type': 'text/event-stream' }),
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body: stream
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});
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// Second request for reconnection
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fetchMock.mockResolvedValueOnce({
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ok: true,
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status: 200,
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headers: new Headers({ 'content-type': 'text/event-stream' }),
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body: new ReadableStream()
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});
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await transport.start();
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await transport['_startOrAuthSse']({});
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// Wait for stream to process and close
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await vi.advanceTimersByTimeAsync(50);
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// Wait for reconnection delay (100ms from retry field)
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await vi.advanceTimersByTimeAsync(150);
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// Should have attempted reconnection
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expect(fetchMock).toHaveBeenCalledTimes(2);
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expect(fetchMock.mock.calls[0][1]?.method).toBe('GET');
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expect(fetchMock.mock.calls[1][1]?.method).toBe('GET');
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// Second call should include Last-Event-ID
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const secondCallHeaders = fetchMock.mock.calls[1][1]?.headers;
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expect(secondCallHeaders?.get('last-event-id')).toBe('evt-1');
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});
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});
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describe('prevent infinite recursion when server returns 401 after successful auth', () => {
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it('should throw error when server returns 401 after successful auth', async () => {
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const message: JSONRPCMessage = {
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