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fix(server): surface parse/validation transport errors via onerror in streamable HTTP #1684

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fix(server): surface parse/validation transport errors via onerror in streamable HTTP #1684

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6 changes: 4 additions & 2 deletions packages/server/src/server/streamableHttp.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -635,7 +635,8 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
if (options?.parsedBody === undefined) {
try {
rawMessage = await req.json();
} catch {
} catch (error) {
this.onerror?.(error instanceof Error ? error : new Error(String(error)));
return this.createJsonErrorResponse(400, -32_700, 'Parse error: Invalid JSON');
}
} else {
Expand All @@ -649,7 +650,8 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
messages = Array.isArray(rawMessage)
? rawMessage.map(msg => JSONRPCMessageSchema.parse(msg))
: [JSONRPCMessageSchema.parse(rawMessage)];
} catch {
} catch (error) {
this.onerror?.(error instanceof Error ? error : new Error(String(error)));
return this.createJsonErrorResponse(400, -32_700, 'Parse error: Invalid JSON-RPC message');
}

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38 changes: 38 additions & 0 deletions packages/server/test/server/streamableHttp.test.ts
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Expand Up @@ -333,6 +333,44 @@ describe('Zod v4', () => {
expectErrorResponse(errorData, -32_700, /Parse error.*Invalid JSON/);
});

it('should call onerror for invalid JSON', async () => {
const errorSpy = vi.fn();
transport.onerror = errorSpy;

const request = new Request('http://localhost/mcp', {
method: 'POST',
headers: {
Accept: 'application/json, text/event-stream',
'Content-Type': 'application/json'
},
body: 'not valid json'
});

const response = await transport.handleRequest(request);

expect(response.status).toBe(400);
expect(errorSpy).toHaveBeenCalledTimes(1);
});

it('should call onerror for invalid JSON-RPC message', async () => {
const errorSpy = vi.fn();
transport.onerror = errorSpy;

const request = new Request('http://localhost/mcp', {
method: 'POST',
headers: {
Accept: 'application/json, text/event-stream',
'Content-Type': 'application/json'
},
body: JSON.stringify({ bad: 'shape' })
});

const response = await transport.handleRequest(request);

expect(response.status).toBe(400);
expect(errorSpy).toHaveBeenCalledTimes(1);
});

it('should accept notifications without session and return 202', async () => {
sessionId = await initializeServer();

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