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test(node): make SSE tests robust to chunked delivery #2833

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test(node): make SSE tests robust to chunked delivery #2833

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28 changes: 21 additions & 7 deletions packages/middleware/node/test/streamableHttp.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -104,6 +104,23 @@ async function readSSEEvent(response: Response): Promise<string> {
return new TextDecoder().decode(value);
}

/**
* Read from an SSE response until the accumulated text satisfies the predicate,
* or the stream ends. Fetch may deliver SSE events in separate chunks, so tests
* must not assume a single read contains every event.
*/
async function readSSEEventUntil(reader: ReadableStreamDefaultReader<Uint8Array>, predicate: (text: string) => boolean): Promise<string> {
const decoder = new TextDecoder();
let text = '';
for (;;) {
const { value, done } = await reader.read();
if (value) text += decoder.decode(value, { stream: true });
if (predicate(text)) break;
if (done) break;
}
return text;
}

/**
* Helper to send JSON-RPC request
*/
Expand Down Expand Up @@ -727,9 +744,8 @@ describe('Zod v4', () => {

const reader = response.body?.getReader();

// The responses may come in any order or together in one chunk
const { value } = await reader!.read();
const text = new TextDecoder().decode(value);
// The responses may arrive in any order or in separate chunks
const text = await readSSEEventUntil(reader!, t => t.includes('"id":"req-1"') && t.includes('"id":"req-2"'));

// Check that both responses were sent on the same stream
expect(text).toContain('"id":"req-1"');
Expand Down Expand Up @@ -1482,8 +1498,7 @@ describe('Zod v4', () => {

// Read the notification from the SSE stream
const reader = sseResponse.body?.getReader();
const { value } = await reader!.read();
const text = new TextDecoder().decode(value);
const text = await readSSEEventUntil(reader!, t => t.includes('First notification from MCP server') && t.includes('id: '));

// Verify the notification was sent with an event ID
expect(text).toContain('id: ');
Expand Down Expand Up @@ -1515,8 +1530,7 @@ describe('Zod v4', () => {

// Read the replayed notification
const reconnectReader = reconnectResponse.body?.getReader();
const reconnectData = await reconnectReader!.read();
const reconnectText = new TextDecoder().decode(reconnectData.value);
const reconnectText = await readSSEEventUntil(reconnectReader!, t => t.includes('Second notification from MCP server'));

// Verify we received the second notification that was sent after our stored eventId
expect(reconnectText).toContain('Second notification from MCP server');
Expand Down
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