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fix: call onerror callback for all error responses in StreamableHTTPServerTransport #1687

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d67929f
fix: call onerror callback for all error responses in StreamableHTTPS…
Mar 16, 2026
df897d7
Add changeset for onerror callback fix
Mar 16, 2026
15514e5
fix: resolve typecheck and lint errors in streamableHttp tests
Mar 16, 2026
3a1a8b7
fix: address review feedback - handleUnsupportedRequest centralizatio…
Mar 17, 2026
30ff76b
fix: format streamableHttp.ts with prettier
Mar 17, 2026
5fcc3b1
test(server): add regression coverage for onerror unsupported-method …
Maverick-666 Mar 17, 2026
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5 changes: 5 additions & 0 deletions .changeset/fix-silent-errors.md
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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
"@modelcontextprotocol/sdk": patch
---

Fix silent transport errors by ensuring onerror callback is invoked for all error responses in StreamableHTTPServerTransport
34 changes: 10 additions & 24 deletions packages/server/src/server/streamableHttp.ts
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Open in desktop
Original file line numberDiff line numberDiff line change
Expand Up@@ -284,9 +284,10 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
status: number,
code: number,
message: string,
options?: { headers?: Record<string, string>; data?: string }
options?: { headers?: Record<string, string>; data?: string; cause?: Error }
): Response {
const error: { code: number; message: string; data?: string } = { code, message };
this.onerror?.(options?.cause ?? new Error(message));
if (options?.data !== undefined) {
error.data = options.data;
}
Expand DownExpand Up@@ -321,7 +322,6 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
const hostHeader = req.headers.get('host');
if (!hostHeader || !this._allowedHosts.includes(hostHeader)) {
const error = `Invalid Host header: ${hostHeader}`;
this.onerror?.(new Error(error));
return this.createJsonErrorResponse(403, -32_000, error);
}
}
Expand All@@ -331,7 +331,6 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
const originHeader = req.headers.get('origin');
if (originHeader && !this._allowedOrigins.includes(originHeader)) {
const error = `Invalid Origin header: ${originHeader}`;
this.onerror?.(new Error(error));
return this.createJsonErrorResponse(403, -32_000, error);
}
}
Expand DownExpand Up@@ -553,8 +552,7 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
});

return new Response(readable, { headers });
} catch (error) {
this.onerror?.(error as Error);
} catch {
return this.createJsonErrorResponse(500, -32_000, 'Error replaying events');
}
}
Expand DownExpand Up@@ -586,23 +584,9 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
* Handles unsupported requests (`PUT`, `PATCH`, etc.)
*/
private handleUnsupportedRequest(): Response {
return Response.json(
{
jsonrpc: '2.0',
error: {
code: -32_000,
message: 'Method not allowed.'
},
id: null
},
{
status: 405,
headers: {
Allow: 'GET, POST, DELETE',
'Content-Type': 'application/json'
}
}
);
return this.createJsonErrorResponse(405, -32_000, 'Method not allowed.', {
headers: { Allow: 'GET, POST, DELETE' }
});
}

/**
Expand DownExpand Up@@ -807,8 +791,10 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
return new Response(readable, { status: 200, headers });
} catch (error) {
// return JSON-RPC formatted error
this.onerror?.(error as Error);
return this.createJsonErrorResponse(400, -32_700, 'Parse error', { data: String(error) });
return this.createJsonErrorResponse(400, -32_700, 'Parse error', {
data: String(error),
cause: error instanceof Error ? error : new Error(String(error))
});
}
}

Expand Down
103 changes: 103 additions & 0 deletions packages/server/test/server/streamableHttp.test.ts
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Original file line numberDiff line numberDiff line change
Expand Up@@ -765,4 +765,107 @@ describe('Zod v4', () => {
await expect(transport.start()).rejects.toThrow('Transport already started');
});
});

describe('HTTPServerTransport - onerror callback', () => {
let transport: WebStandardStreamableHTTPServerTransport;
let errors: Error[];

beforeEach(async () => {
transport = new WebStandardStreamableHTTPServerTransport({
sessionIdGenerator: () => randomUUID()
});
errors = [];
transport.onerror = error => errors.push(error);
await transport.start();
});

it('should call onerror for invalid Accept header on POST', async () => {
const request = createRequest('POST', TEST_MESSAGES.initialize, { accept: 'application/json' });
const response = await transport.handleRequest(request);

expect(response.status).toBe(406);
expect(errors.length).toBe(1);
expect(errors[0]!.message).toMatch(/Not Acceptable/);
});

it('should call onerror for invalid Content-Type on POST', async () => {
const request = new Request('http://localhost/mcp', {
method: 'POST',
headers: {
Accept: 'application/json, text/event-stream',
'Content-Type': 'text/plain'
},
body: JSON.stringify(TEST_MESSAGES.initialize)
});
const response = await transport.handleRequest(request);

expect(response.status).toBe(415);
expect(errors.length).toBe(1);
expect(errors[0]!.message).toMatch(/Unsupported Media Type/);
});

it('should call onerror for invalid JSON on POST', async () => {
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(errors.length).toBe(1);
expect(errors[0]!.message).toMatch(/Parse error/);
});

it('should call onerror for invalid JSON-RPC message on POST', async () => {
const request = new Request('http://localhost/mcp', {
method: 'POST',
headers: {
Accept: 'application/json, text/event-stream',
'Content-Type': 'application/json'
},
body: JSON.stringify({ not: 'a jsonrpc message' })
});
const response = await transport.handleRequest(request);

expect(response.status).toBe(400);
expect(errors.length).toBe(1);
expect(errors[0]!.message).toMatch(/Parse error.*Invalid JSON-RPC/);
});

it('should call onerror for invalid Accept header on GET', async () => {
const request = createRequest('GET', undefined, { accept: 'application/json' });
const response = await transport.handleRequest(request);

expect(response.status).toBe(406);
expect(errors.length).toBe(1);
expect(errors[0]!.message).toMatch(/Not Acceptable/);
});

it('should call onerror for unsupported HTTP methods', async () => {
const request = new Request('http://localhost/mcp', { method: 'PUT' });
const response = await transport.handleRequest(request);

expect(response.status).toBe(405);
expect(errors.length).toBe(1);
expect(errors[0]!.message).toBe('Method not allowed.');
});

it('should preserve original error object when createJsonErrorResponse receives cause', async () => {
const thrown = new Error('boom-from-onmessage');
transport.onmessage = () => {
throw thrown;
};

const request = createRequest('POST', TEST_MESSAGES.initialize);
const response = await transport.handleRequest(request);

expect(response.status).toBe(400);
expect(errors.length).toBe(1);
expect(errors[0]).toBe(thrown);
});
});
});
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fix: call onerror callback for all error responses in StreamableHTTPServerTransport by kdn-posipaka · Pull Request #1687 · modelcontextprotocol/typescript-sdk · GitHub
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fix: call onerror callback for all error responses in StreamableHTTPServerTransport#1687

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fix: call onerror callback for all error responses in StreamableHTTPServerTransport
#1687
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d67929f

fix: call onerror callback for all error responses in StreamableHTTPS…

Mar 16, 2026
df897d7

Add changeset for onerror callback fix

Mar 16, 2026
15514e5

fix: resolve typecheck and lint errors in streamableHttp tests

Mar 16, 2026
3a1a8b7

fix: address review feedback - handleUnsupportedRequest centralizatio…

Mar 17, 2026
30ff76b

fix: format streamableHttp.ts with prettier

Mar 17, 2026
5fcc3b1

test(server): add regression coverage for onerror unsupported-method …


Maverick-666 Mar 17, 2026

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5 changes: 5 additions & 0 deletions
.changeset/fix-silent-errors.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
"@modelcontextprotocol/sdk": patch
---

Fix silent transport errors by ensuring onerror callback is invoked for all error responses in StreamableHTTPServerTransport

34 changes: 10 additions & 24 deletions
packages/server/src/server/streamableHttp.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -284,9 +284,10 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 status: number,
 code: number,
 message: string,
 options?: { headers?: Record<string, string>; data?: string }
 options?: { headers?: Record<string, string>; data?: string; cause?: Error }
 ): Response {
 const error: { code: number; message: string; data?: string } = { code, message };
 this.onerror?.(options?.cause ?? new Error(message));
 if (options?.data !== undefined) {
 error.data = options.data;
 }
Expand DownExpand Up@@ -321,7 +322,6 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 const hostHeader = req.headers.get('host');
 if (!hostHeader || !this._allowedHosts.includes(hostHeader)) {
 const error = `Invalid Host header: ${hostHeader}`;
 this.onerror?.(new Error(error));
 return this.createJsonErrorResponse(403, -32_000, error);
 }
 }
Expand All@@ -331,7 +331,6 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 const originHeader = req.headers.get('origin');
 if (originHeader && !this._allowedOrigins.includes(originHeader)) {
 const error = `Invalid Origin header: ${originHeader}`;
 this.onerror?.(new Error(error));
 return this.createJsonErrorResponse(403, -32_000, error);
 }
 }
Expand DownExpand Up@@ -553,8 +552,7 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 });

 return new Response(readable, { headers });
 } catch (error) {
 this.onerror?.(error as Error);
 } catch {
 return this.createJsonErrorResponse(500, -32_000, 'Error replaying events');
 }
 }
Expand DownExpand Up@@ -586,23 +584,9 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 * Handles unsupported requests (`PUT`, `PATCH`, etc.)
 */
 private handleUnsupportedRequest(): Response {
 return Response.json(
 {
 jsonrpc: '2.0',
 error: {
 code: -32_000,
 message: 'Method not allowed.'
 },
 id: null
 },
 {
 status: 405,
 headers: {
 Allow: 'GET, POST, DELETE',
 'Content-Type': 'application/json'
 }
 }
 );
 return this.createJsonErrorResponse(405, -32_000, 'Method not allowed.', {
 headers: { Allow: 'GET, POST, DELETE' }
 });
 }

 /**
Expand DownExpand Up@@ -807,8 +791,10 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 return new Response(readable, { status: 200, headers });
 } catch (error) {
 // return JSON-RPC formatted error
 this.onerror?.(error as Error);
 return this.createJsonErrorResponse(400, -32_700, 'Parse error', { data: String(error) });
 return this.createJsonErrorResponse(400, -32_700, 'Parse error', {
 data: String(error),
 cause: error instanceof Error ? error : new Error(String(error))
 });
 }
 }

Expand Down

103 changes: 103 additions & 0 deletions
packages/server/test/server/streamableHttp.test.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -765,4 +765,107 @@ describe('Zod v4', () => {
 await expect(transport.start()).rejects.toThrow('Transport already started');
 });
 });

 describe('HTTPServerTransport - onerror callback', () => {
 let transport: WebStandardStreamableHTTPServerTransport;
 let errors: Error[];

 beforeEach(async () => {
 transport = new WebStandardStreamableHTTPServerTransport({
 sessionIdGenerator: () => randomUUID()
 });
 errors = [];
 transport.onerror = error => errors.push(error);
 await transport.start();
 });

 it('should call onerror for invalid Accept header on POST', async () => {
 const request = createRequest('POST', TEST_MESSAGES.initialize, { accept: 'application/json' });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(406);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Not Acceptable/);
 });

 it('should call onerror for invalid Content-Type on POST', async () => {
 const request = new Request('http://localhost/mcp', {
 method: 'POST',
 headers: {
 Accept: 'application/json, text/event-stream',
 'Content-Type': 'text/plain'
 },
 body: JSON.stringify(TEST_MESSAGES.initialize)
 });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(415);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Unsupported Media Type/);
 });

 it('should call onerror for invalid JSON on POST', async () => {
 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(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Parse error/);
 });

 it('should call onerror for invalid JSON-RPC message on POST', async () => {
 const request = new Request('http://localhost/mcp', {
 method: 'POST',
 headers: {
 Accept: 'application/json, text/event-stream',
 'Content-Type': 'application/json'
 },
 body: JSON.stringify({ not: 'a jsonrpc message' })
 });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(400);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Parse error.*Invalid JSON-RPC/);
 });

 it('should call onerror for invalid Accept header on GET', async () => {
 const request = createRequest('GET', undefined, { accept: 'application/json' });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(406);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Not Acceptable/);
 });

 it('should call onerror for unsupported HTTP methods', async () => {
 const request = new Request('http://localhost/mcp', { method: 'PUT' });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(405);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toBe('Method not allowed.');
 });

 it('should preserve original error object when createJsonErrorResponse receives cause', async () => {
 const thrown = new Error('boom-from-onmessage');
 transport.onmessage = () => {
 throw thrown;
 };

 const request = createRequest('POST', TEST_MESSAGES.initialize);
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(400);
 expect(errors.length).toBe(1);
 expect(errors[0]).toBe(thrown);
 });
 });
});
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fix: call onerror callback for all error responses in StreamableHTTPServerTransport by kdn-posipaka · Pull Request #1687 · modelcontextprotocol/typescript-sdk · GitHub
Skip to content
fix: call onerror callback for all error responses in StreamableHTTPServerTransport#1687

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 Closed

kdn-posipaka
wants to merge
6
commits into

from

 Closed


fix: call onerror callback for all error responses in StreamableHTTPServerTransport
#1687
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6 commits


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d67929f

fix: call onerror callback for all error responses in StreamableHTTPS…

Mar 16, 2026
df897d7

Add changeset for onerror callback fix

Mar 16, 2026
15514e5

fix: resolve typecheck and lint errors in streamableHttp tests

Mar 16, 2026
3a1a8b7

fix: address review feedback - handleUnsupportedRequest centralizatio…

Mar 17, 2026
30ff76b

fix: format streamableHttp.ts with prettier

Mar 17, 2026
5fcc3b1

test(server): add regression coverage for onerror unsupported-method …


Maverick-666 Mar 17, 2026

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5 changes: 5 additions & 0 deletions
.changeset/fix-silent-errors.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
"@modelcontextprotocol/sdk": patch
---

Fix silent transport errors by ensuring onerror callback is invoked for all error responses in StreamableHTTPServerTransport

34 changes: 10 additions & 24 deletions
packages/server/src/server/streamableHttp.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -284,9 +284,10 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 status: number,
 code: number,
 message: string,
 options?: { headers?: Record<string, string>; data?: string }
 options?: { headers?: Record<string, string>; data?: string; cause?: Error }
 ): Response {
 const error: { code: number; message: string; data?: string } = { code, message };
 this.onerror?.(options?.cause ?? new Error(message));
 if (options?.data !== undefined) {
 error.data = options.data;
 }
Expand DownExpand Up@@ -321,7 +322,6 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 const hostHeader = req.headers.get('host');
 if (!hostHeader || !this._allowedHosts.includes(hostHeader)) {
 const error = `Invalid Host header: ${hostHeader}`;
 this.onerror?.(new Error(error));
 return this.createJsonErrorResponse(403, -32_000, error);
 }
 }
Expand All@@ -331,7 +331,6 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 const originHeader = req.headers.get('origin');
 if (originHeader && !this._allowedOrigins.includes(originHeader)) {
 const error = `Invalid Origin header: ${originHeader}`;
 this.onerror?.(new Error(error));
 return this.createJsonErrorResponse(403, -32_000, error);
 }
 }
Expand DownExpand Up@@ -553,8 +552,7 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 });

 return new Response(readable, { headers });
 } catch (error) {
 this.onerror?.(error as Error);
 } catch {
 return this.createJsonErrorResponse(500, -32_000, 'Error replaying events');
 }
 }
Expand DownExpand Up@@ -586,23 +584,9 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 * Handles unsupported requests (`PUT`, `PATCH`, etc.)
 */
 private handleUnsupportedRequest(): Response {
 return Response.json(
 {
 jsonrpc: '2.0',
 error: {
 code: -32_000,
 message: 'Method not allowed.'
 },
 id: null
 },
 {
 status: 405,
 headers: {
 Allow: 'GET, POST, DELETE',
 'Content-Type': 'application/json'
 }
 }
 );
 return this.createJsonErrorResponse(405, -32_000, 'Method not allowed.', {
 headers: { Allow: 'GET, POST, DELETE' }
 });
 }

 /**
Expand DownExpand Up@@ -807,8 +791,10 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 return new Response(readable, { status: 200, headers });
 } catch (error) {
 // return JSON-RPC formatted error
 this.onerror?.(error as Error);
 return this.createJsonErrorResponse(400, -32_700, 'Parse error', { data: String(error) });
 return this.createJsonErrorResponse(400, -32_700, 'Parse error', {
 data: String(error),
 cause: error instanceof Error ? error : new Error(String(error))
 });
 }
 }

Expand Down

103 changes: 103 additions & 0 deletions
packages/server/test/server/streamableHttp.test.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -765,4 +765,107 @@ describe('Zod v4', () => {
 await expect(transport.start()).rejects.toThrow('Transport already started');
 });
 });

 describe('HTTPServerTransport - onerror callback', () => {
 let transport: WebStandardStreamableHTTPServerTransport;
 let errors: Error[];

 beforeEach(async () => {
 transport = new WebStandardStreamableHTTPServerTransport({
 sessionIdGenerator: () => randomUUID()
 });
 errors = [];
 transport.onerror = error => errors.push(error);
 await transport.start();
 });

 it('should call onerror for invalid Accept header on POST', async () => {
 const request = createRequest('POST', TEST_MESSAGES.initialize, { accept: 'application/json' });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(406);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Not Acceptable/);
 });

 it('should call onerror for invalid Content-Type on POST', async () => {
 const request = new Request('http://localhost/mcp', {
 method: 'POST',
 headers: {
 Accept: 'application/json, text/event-stream',
 'Content-Type': 'text/plain'
 },
 body: JSON.stringify(TEST_MESSAGES.initialize)
 });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(415);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Unsupported Media Type/);
 });

 it('should call onerror for invalid JSON on POST', async () => {
 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(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Parse error/);
 });

 it('should call onerror for invalid JSON-RPC message on POST', async () => {
 const request = new Request('http://localhost/mcp', {
 method: 'POST',
 headers: {
 Accept: 'application/json, text/event-stream',
 'Content-Type': 'application/json'
 },
 body: JSON.stringify({ not: 'a jsonrpc message' })
 });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(400);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Parse error.*Invalid JSON-RPC/);
 });

 it('should call onerror for invalid Accept header on GET', async () => {
 const request = createRequest('GET', undefined, { accept: 'application/json' });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(406);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Not Acceptable/);
 });

 it('should call onerror for unsupported HTTP methods', async () => {
 const request = new Request('http://localhost/mcp', { method: 'PUT' });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(405);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toBe('Method not allowed.');
 });

 it('should preserve original error object when createJsonErrorResponse receives cause', async () => {
 const thrown = new Error('boom-from-onmessage');
 transport.onmessage = () => {
 throw thrown;
 };

 const request = createRequest('POST', TEST_MESSAGES.initialize);
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(400);
 expect(errors.length).toBe(1);
 expect(errors[0]).toBe(thrown);
 });
 });
});
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Highlight search terms from Google/DuckDuckGo/Bing referrer
(function() {
var ref = document.referrer;
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if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {
var url = new URL(ref);
var q = url.searchParams.get('q') || url.searchParams.get('p');
if (q) {
terms = q.split(/\s+/).filter(function(t) { return t.length > 2; });
}
}
if (terms.length === 0) return;
var style = document.createElement('style');
style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';
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function highlight(node) {
if (node.nodeType === 3) { // text node
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terms.forEach(function(term) {
var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\]\\]/g, '\\') + ')', 'gi');
if (regex.test(text)) {
found = true;
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var parts = text.split(regex);
parts.forEach(function(part, i) {
if (i % 2 === 0) {
frag.appendChild(document.createTextNode(part));
} else {
var span = document.createElement('span');
span.className = 'userscript-highlight';
span.textContent = part;
frag.appendChild(span);
}
});
node.parentNode.replaceChild(frag, node);
}
});
} else if (node.nodeType === 1 && node.childNodes) { // element
var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];
if (!skipTags.includes(node.tagName)) {
Array.from(node.childNodes).forEach(highlight);
}
}
}
highlight(document.body);
// Re-highlight on dynamic content
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1 || node.nodeType === 3) highlight(node);
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
fix: call onerror callback for all error responses in StreamableHTTPServerTransport by kdn-posipaka · Pull Request #1687 · modelcontextprotocol/typescript-sdk · GitHub
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fix: call onerror callback for all error responses in StreamableHTTPServerTransport#1687

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fix: call onerror callback for all error responses in StreamableHTTPServerTransport
#1687
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d67929f

fix: call onerror callback for all error responses in StreamableHTTPS…

Mar 16, 2026
df897d7

Add changeset for onerror callback fix

Mar 16, 2026
15514e5

fix: resolve typecheck and lint errors in streamableHttp tests

Mar 16, 2026
3a1a8b7

fix: address review feedback - handleUnsupportedRequest centralizatio…

Mar 17, 2026
30ff76b

fix: format streamableHttp.ts with prettier

Mar 17, 2026
5fcc3b1

test(server): add regression coverage for onerror unsupported-method …


Maverick-666 Mar 17, 2026

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5 changes: 5 additions & 0 deletions
.changeset/fix-silent-errors.md

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
"@modelcontextprotocol/sdk": patch
---

Fix silent transport errors by ensuring onerror callback is invoked for all error responses in StreamableHTTPServerTransport

34 changes: 10 additions & 24 deletions
packages/server/src/server/streamableHttp.ts

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -284,9 +284,10 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 status: number,
 code: number,
 message: string,
 options?: { headers?: Record<string, string>; data?: string }
 options?: { headers?: Record<string, string>; data?: string; cause?: Error }
 ): Response {
 const error: { code: number; message: string; data?: string } = { code, message };
 this.onerror?.(options?.cause ?? new Error(message));
 if (options?.data !== undefined) {
 error.data = options.data;
 }
Expand DownExpand Up@@ -321,7 +322,6 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 const hostHeader = req.headers.get('host');
 if (!hostHeader || !this._allowedHosts.includes(hostHeader)) {
 const error = `Invalid Host header: ${hostHeader}`;
 this.onerror?.(new Error(error));
 return this.createJsonErrorResponse(403, -32_000, error);
 }
 }
Expand All@@ -331,7 +331,6 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 const originHeader = req.headers.get('origin');
 if (originHeader && !this._allowedOrigins.includes(originHeader)) {
 const error = `Invalid Origin header: ${originHeader}`;
 this.onerror?.(new Error(error));
 return this.createJsonErrorResponse(403, -32_000, error);
 }
 }
Expand DownExpand Up@@ -553,8 +552,7 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 });

 return new Response(readable, { headers });
 } catch (error) {
 this.onerror?.(error as Error);
 } catch {
 return this.createJsonErrorResponse(500, -32_000, 'Error replaying events');
 }
 }
Expand DownExpand Up@@ -586,23 +584,9 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 * Handles unsupported requests (`PUT`, `PATCH`, etc.)
 */
 private handleUnsupportedRequest(): Response {
 return Response.json(
 {
 jsonrpc: '2.0',
 error: {
 code: -32_000,
 message: 'Method not allowed.'
 },
 id: null
 },
 {
 status: 405,
 headers: {
 Allow: 'GET, POST, DELETE',
 'Content-Type': 'application/json'
 }
 }
 );
 return this.createJsonErrorResponse(405, -32_000, 'Method not allowed.', {
 headers: { Allow: 'GET, POST, DELETE' }
 });
 }

 /**
Expand DownExpand Up@@ -807,8 +791,10 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 return new Response(readable, { status: 200, headers });
 } catch (error) {
 // return JSON-RPC formatted error
 this.onerror?.(error as Error);
 return this.createJsonErrorResponse(400, -32_700, 'Parse error', { data: String(error) });
 return this.createJsonErrorResponse(400, -32_700, 'Parse error', {
 data: String(error),
 cause: error instanceof Error ? error : new Error(String(error))
 });
 }
 }

Expand Down

103 changes: 103 additions & 0 deletions
packages/server/test/server/streamableHttp.test.ts

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Original file line numberDiff line numberDiff line change
Expand Up@@ -765,4 +765,107 @@ describe('Zod v4', () => {
 await expect(transport.start()).rejects.toThrow('Transport already started');
 });
 });

 describe('HTTPServerTransport - onerror callback', () => {
 let transport: WebStandardStreamableHTTPServerTransport;
 let errors: Error[];

 beforeEach(async () => {
 transport = new WebStandardStreamableHTTPServerTransport({
 sessionIdGenerator: () => randomUUID()
 });
 errors = [];
 transport.onerror = error => errors.push(error);
 await transport.start();
 });

 it('should call onerror for invalid Accept header on POST', async () => {
 const request = createRequest('POST', TEST_MESSAGES.initialize, { accept: 'application/json' });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(406);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Not Acceptable/);
 });

 it('should call onerror for invalid Content-Type on POST', async () => {
 const request = new Request('http://localhost/mcp', {
 method: 'POST',
 headers: {
 Accept: 'application/json, text/event-stream',
 'Content-Type': 'text/plain'
 },
 body: JSON.stringify(TEST_MESSAGES.initialize)
 });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(415);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Unsupported Media Type/);
 });

 it('should call onerror for invalid JSON on POST', async () => {
 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(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Parse error/);
 });

 it('should call onerror for invalid JSON-RPC message on POST', async () => {
 const request = new Request('http://localhost/mcp', {
 method: 'POST',
 headers: {
 Accept: 'application/json, text/event-stream',
 'Content-Type': 'application/json'
 },
 body: JSON.stringify({ not: 'a jsonrpc message' })
 });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(400);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Parse error.*Invalid JSON-RPC/);
 });

 it('should call onerror for invalid Accept header on GET', async () => {
 const request = createRequest('GET', undefined, { accept: 'application/json' });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(406);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Not Acceptable/);
 });

 it('should call onerror for unsupported HTTP methods', async () => {
 const request = new Request('http://localhost/mcp', { method: 'PUT' });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(405);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toBe('Method not allowed.');
 });

 it('should preserve original error object when createJsonErrorResponse receives cause', async () => {
 const thrown = new Error('boom-from-onmessage');
 transport.onmessage = () => {
 throw thrown;
 };

 const request = createRequest('POST', TEST_MESSAGES.initialize);
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(400);
 expect(errors.length).toBe(1);
 expect(errors[0]).toBe(thrown);
 });
 });
});
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Strip utm_, fbclid, gclid, etc. from all links on page
(function() {
var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',
'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',
'ref', 'ref_src', 'source', 'medium', 'campaign'];
function cleanUrl(url) {
try {
var u = new URL(url, window.location.origin);
var changed = false;
trackingParams.forEach(function(p) {
if (u.searchParams.has(p)) {
u.searchParams.delete(p);
changed = true;
}
});
return changed ? u.toString() : url;
} catch (e) {
return url;
}
}
function cleanLinks() {
document.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
cleanLinks();
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1) {
if (node.tagName === 'A') cleanLinks();
node.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '
fix: call onerror callback for all error responses in StreamableHTTPServerTransport by kdn-posipaka · Pull Request #1687 · modelcontextprotocol/typescript-sdk · GitHub
Skip to content
fix: call onerror callback for all error responses in StreamableHTTPServerTransport#1687

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kdn-posipaka
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6
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 Closed


fix: call onerror callback for all error responses in StreamableHTTPServerTransport
#1687
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d67929f

fix: call onerror callback for all error responses in StreamableHTTPS…

Mar 16, 2026
df897d7

Add changeset for onerror callback fix

Mar 16, 2026
15514e5

fix: resolve typecheck and lint errors in streamableHttp tests

Mar 16, 2026
3a1a8b7

fix: address review feedback - handleUnsupportedRequest centralizatio…

Mar 17, 2026
30ff76b

fix: format streamableHttp.ts with prettier

Mar 17, 2026
5fcc3b1

test(server): add regression coverage for onerror unsupported-method …


Maverick-666 Mar 17, 2026

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5 changes: 5 additions & 0 deletions
.changeset/fix-silent-errors.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
"@modelcontextprotocol/sdk": patch
---

Fix silent transport errors by ensuring onerror callback is invoked for all error responses in StreamableHTTPServerTransport

34 changes: 10 additions & 24 deletions
packages/server/src/server/streamableHttp.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -284,9 +284,10 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 status: number,
 code: number,
 message: string,
 options?: { headers?: Record<string, string>; data?: string }
 options?: { headers?: Record<string, string>; data?: string; cause?: Error }
 ): Response {
 const error: { code: number; message: string; data?: string } = { code, message };
 this.onerror?.(options?.cause ?? new Error(message));
 if (options?.data !== undefined) {
 error.data = options.data;
 }
Expand DownExpand Up@@ -321,7 +322,6 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 const hostHeader = req.headers.get('host');
 if (!hostHeader || !this._allowedHosts.includes(hostHeader)) {
 const error = `Invalid Host header: ${hostHeader}`;
 this.onerror?.(new Error(error));
 return this.createJsonErrorResponse(403, -32_000, error);
 }
 }
Expand All@@ -331,7 +331,6 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 const originHeader = req.headers.get('origin');
 if (originHeader && !this._allowedOrigins.includes(originHeader)) {
 const error = `Invalid Origin header: ${originHeader}`;
 this.onerror?.(new Error(error));
 return this.createJsonErrorResponse(403, -32_000, error);
 }
 }
Expand DownExpand Up@@ -553,8 +552,7 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 });

 return new Response(readable, { headers });
 } catch (error) {
 this.onerror?.(error as Error);
 } catch {
 return this.createJsonErrorResponse(500, -32_000, 'Error replaying events');
 }
 }
Expand DownExpand Up@@ -586,23 +584,9 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 * Handles unsupported requests (`PUT`, `PATCH`, etc.)
 */
 private handleUnsupportedRequest(): Response {
 return Response.json(
 {
 jsonrpc: '2.0',
 error: {
 code: -32_000,
 message: 'Method not allowed.'
 },
 id: null
 },
 {
 status: 405,
 headers: {
 Allow: 'GET, POST, DELETE',
 'Content-Type': 'application/json'
 }
 }
 );
 return this.createJsonErrorResponse(405, -32_000, 'Method not allowed.', {
 headers: { Allow: 'GET, POST, DELETE' }
 });
 }

 /**
Expand DownExpand Up@@ -807,8 +791,10 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 return new Response(readable, { status: 200, headers });
 } catch (error) {
 // return JSON-RPC formatted error
 this.onerror?.(error as Error);
 return this.createJsonErrorResponse(400, -32_700, 'Parse error', { data: String(error) });
 return this.createJsonErrorResponse(400, -32_700, 'Parse error', {
 data: String(error),
 cause: error instanceof Error ? error : new Error(String(error))
 });
 }
 }

Expand Down

103 changes: 103 additions & 0 deletions
packages/server/test/server/streamableHttp.test.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -765,4 +765,107 @@ describe('Zod v4', () => {
 await expect(transport.start()).rejects.toThrow('Transport already started');
 });
 });

 describe('HTTPServerTransport - onerror callback', () => {
 let transport: WebStandardStreamableHTTPServerTransport;
 let errors: Error[];

 beforeEach(async () => {
 transport = new WebStandardStreamableHTTPServerTransport({
 sessionIdGenerator: () => randomUUID()
 });
 errors = [];
 transport.onerror = error => errors.push(error);
 await transport.start();
 });

 it('should call onerror for invalid Accept header on POST', async () => {
 const request = createRequest('POST', TEST_MESSAGES.initialize, { accept: 'application/json' });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(406);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Not Acceptable/);
 });

 it('should call onerror for invalid Content-Type on POST', async () => {
 const request = new Request('http://localhost/mcp', {
 method: 'POST',
 headers: {
 Accept: 'application/json, text/event-stream',
 'Content-Type': 'text/plain'
 },
 body: JSON.stringify(TEST_MESSAGES.initialize)
 });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(415);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Unsupported Media Type/);
 });

 it('should call onerror for invalid JSON on POST', async () => {
 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(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Parse error/);
 });

 it('should call onerror for invalid JSON-RPC message on POST', async () => {
 const request = new Request('http://localhost/mcp', {
 method: 'POST',
 headers: {
 Accept: 'application/json, text/event-stream',
 'Content-Type': 'application/json'
 },
 body: JSON.stringify({ not: 'a jsonrpc message' })
 });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(400);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Parse error.*Invalid JSON-RPC/);
 });

 it('should call onerror for invalid Accept header on GET', async () => {
 const request = createRequest('GET', undefined, { accept: 'application/json' });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(406);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Not Acceptable/);
 });

 it('should call onerror for unsupported HTTP methods', async () => {
 const request = new Request('http://localhost/mcp', { method: 'PUT' });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(405);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toBe('Method not allowed.');
 });

 it('should preserve original error object when createJsonErrorResponse receives cause', async () => {
 const thrown = new Error('boom-from-onmessage');
 transport.onmessage = () => {
 throw thrown;
 };

 const request = createRequest('POST', TEST_MESSAGES.initialize);
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(400);
 expect(errors.length).toBe(1);
 expect(errors[0]).toBe(thrown);
 });
 });
});
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Auto-enable theater mode on YouTube
(function() {
function tryTheater() {
var btn = document.querySelector('button[aria-label="Theater mode"], ytd-player #player button[title="Theater mode"]');
if (btn && !btn.classList.contains('activated')) {
btn.click();
}
}
// Try immediately
tryTheater();
// Try after navigation (SPA)
var lastUrl = location.href;
setInterval(function() {
if (location.href !== lastUrl) {
lastUrl = location.href;
setTimeout(tryTheater, 500);
}
}, 1000);
// Also try on player load
var observer = new MutationObserver(tryTheater);
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
fix: call onerror callback for all error responses in StreamableHTTPServerTransport by kdn-posipaka · Pull Request #1687 · modelcontextprotocol/typescript-sdk · GitHub
Skip to content
fix: call onerror callback for all error responses in StreamableHTTPServerTransport#1687

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kdn-posipaka
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commits into

from

 Closed


fix: call onerror callback for all error responses in StreamableHTTPServerTransport
#1687
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d67929f

fix: call onerror callback for all error responses in StreamableHTTPS…

Mar 16, 2026
df897d7

Add changeset for onerror callback fix

Mar 16, 2026
15514e5

fix: resolve typecheck and lint errors in streamableHttp tests

Mar 16, 2026
3a1a8b7

fix: address review feedback - handleUnsupportedRequest centralizatio…

Mar 17, 2026
30ff76b

fix: format streamableHttp.ts with prettier

Mar 17, 2026
5fcc3b1

test(server): add regression coverage for onerror unsupported-method …


Maverick-666 Mar 17, 2026

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5 changes: 5 additions & 0 deletions
.changeset/fix-silent-errors.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
"@modelcontextprotocol/sdk": patch
---

Fix silent transport errors by ensuring onerror callback is invoked for all error responses in StreamableHTTPServerTransport

34 changes: 10 additions & 24 deletions
packages/server/src/server/streamableHttp.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -284,9 +284,10 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 status: number,
 code: number,
 message: string,
 options?: { headers?: Record<string, string>; data?: string }
 options?: { headers?: Record<string, string>; data?: string; cause?: Error }
 ): Response {
 const error: { code: number; message: string; data?: string } = { code, message };
 this.onerror?.(options?.cause ?? new Error(message));
 if (options?.data !== undefined) {
 error.data = options.data;
 }
Expand DownExpand Up@@ -321,7 +322,6 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 const hostHeader = req.headers.get('host');
 if (!hostHeader || !this._allowedHosts.includes(hostHeader)) {
 const error = `Invalid Host header: ${hostHeader}`;
 this.onerror?.(new Error(error));
 return this.createJsonErrorResponse(403, -32_000, error);
 }
 }
Expand All@@ -331,7 +331,6 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 const originHeader = req.headers.get('origin');
 if (originHeader && !this._allowedOrigins.includes(originHeader)) {
 const error = `Invalid Origin header: ${originHeader}`;
 this.onerror?.(new Error(error));
 return this.createJsonErrorResponse(403, -32_000, error);
 }
 }
Expand DownExpand Up@@ -553,8 +552,7 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 });

 return new Response(readable, { headers });
 } catch (error) {
 this.onerror?.(error as Error);
 } catch {
 return this.createJsonErrorResponse(500, -32_000, 'Error replaying events');
 }
 }
Expand DownExpand Up@@ -586,23 +584,9 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 * Handles unsupported requests (`PUT`, `PATCH`, etc.)
 */
 private handleUnsupportedRequest(): Response {
 return Response.json(
 {
 jsonrpc: '2.0',
 error: {
 code: -32_000,
 message: 'Method not allowed.'
 },
 id: null
 },
 {
 status: 405,
 headers: {
 Allow: 'GET, POST, DELETE',
 'Content-Type': 'application/json'
 }
 }
 );
 return this.createJsonErrorResponse(405, -32_000, 'Method not allowed.', {
 headers: { Allow: 'GET, POST, DELETE' }
 });
 }

 /**
Expand DownExpand Up@@ -807,8 +791,10 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 return new Response(readable, { status: 200, headers });
 } catch (error) {
 // return JSON-RPC formatted error
 this.onerror?.(error as Error);
 return this.createJsonErrorResponse(400, -32_700, 'Parse error', { data: String(error) });
 return this.createJsonErrorResponse(400, -32_700, 'Parse error', {
 data: String(error),
 cause: error instanceof Error ? error : new Error(String(error))
 });
 }
 }

Expand Down

103 changes: 103 additions & 0 deletions
packages/server/test/server/streamableHttp.test.ts

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -765,4 +765,107 @@ describe('Zod v4', () => {
 await expect(transport.start()).rejects.toThrow('Transport already started');
 });
 });

 describe('HTTPServerTransport - onerror callback', () => {
 let transport: WebStandardStreamableHTTPServerTransport;
 let errors: Error[];

 beforeEach(async () => {
 transport = new WebStandardStreamableHTTPServerTransport({
 sessionIdGenerator: () => randomUUID()
 });
 errors = [];
 transport.onerror = error => errors.push(error);
 await transport.start();
 });

 it('should call onerror for invalid Accept header on POST', async () => {
 const request = createRequest('POST', TEST_MESSAGES.initialize, { accept: 'application/json' });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(406);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Not Acceptable/);
 });

 it('should call onerror for invalid Content-Type on POST', async () => {
 const request = new Request('http://localhost/mcp', {
 method: 'POST',
 headers: {
 Accept: 'application/json, text/event-stream',
 'Content-Type': 'text/plain'
 },
 body: JSON.stringify(TEST_MESSAGES.initialize)
 });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(415);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Unsupported Media Type/);
 });

 it('should call onerror for invalid JSON on POST', async () => {
 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(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Parse error/);
 });

 it('should call onerror for invalid JSON-RPC message on POST', async () => {
 const request = new Request('http://localhost/mcp', {
 method: 'POST',
 headers: {
 Accept: 'application/json, text/event-stream',
 'Content-Type': 'application/json'
 },
 body: JSON.stringify({ not: 'a jsonrpc message' })
 });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(400);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Parse error.*Invalid JSON-RPC/);
 });

 it('should call onerror for invalid Accept header on GET', async () => {
 const request = createRequest('GET', undefined, { accept: 'application/json' });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(406);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Not Acceptable/);
 });

 it('should call onerror for unsupported HTTP methods', async () => {
 const request = new Request('http://localhost/mcp', { method: 'PUT' });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(405);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toBe('Method not allowed.');
 });

 it('should preserve original error object when createJsonErrorResponse receives cause', async () => {
 const thrown = new Error('boom-from-onmessage');
 transport.onmessage = () => {
 throw thrown;
 };

 const request = createRequest('POST', TEST_MESSAGES.initialize);
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(400);
 expect(errors.length).toBe(1);
 expect(errors[0]).toBe(thrown);
 });
 });
});
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fix: call onerror callback for all error responses in StreamableHTTPServerTransport by kdn-posipaka · Pull Request #1687 · modelcontextprotocol/typescript-sdk · GitHub
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fix: call onerror callback for all error responses in StreamableHTTPServerTransport#1687

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fix: call onerror callback for all error responses in StreamableHTTPServerTransport
#1687
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d67929f

fix: call onerror callback for all error responses in StreamableHTTPS…

Mar 16, 2026
df897d7

Add changeset for onerror callback fix

Mar 16, 2026
15514e5

fix: resolve typecheck and lint errors in streamableHttp tests

Mar 16, 2026
3a1a8b7

fix: address review feedback - handleUnsupportedRequest centralizatio…

Mar 17, 2026
30ff76b

fix: format streamableHttp.ts with prettier

Mar 17, 2026
5fcc3b1

test(server): add regression coverage for onerror unsupported-method …


Maverick-666 Mar 17, 2026

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5 changes: 5 additions & 0 deletions
.changeset/fix-silent-errors.md

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
"@modelcontextprotocol/sdk": patch
---

Fix silent transport errors by ensuring onerror callback is invoked for all error responses in StreamableHTTPServerTransport

34 changes: 10 additions & 24 deletions
packages/server/src/server/streamableHttp.ts

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -284,9 +284,10 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 status: number,
 code: number,
 message: string,
 options?: { headers?: Record<string, string>; data?: string }
 options?: { headers?: Record<string, string>; data?: string; cause?: Error }
 ): Response {
 const error: { code: number; message: string; data?: string } = { code, message };
 this.onerror?.(options?.cause ?? new Error(message));
 if (options?.data !== undefined) {
 error.data = options.data;
 }
Expand DownExpand Up@@ -321,7 +322,6 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 const hostHeader = req.headers.get('host');
 if (!hostHeader || !this._allowedHosts.includes(hostHeader)) {
 const error = `Invalid Host header: ${hostHeader}`;
 this.onerror?.(new Error(error));
 return this.createJsonErrorResponse(403, -32_000, error);
 }
 }
Expand All@@ -331,7 +331,6 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 const originHeader = req.headers.get('origin');
 if (originHeader && !this._allowedOrigins.includes(originHeader)) {
 const error = `Invalid Origin header: ${originHeader}`;
 this.onerror?.(new Error(error));
 return this.createJsonErrorResponse(403, -32_000, error);
 }
 }
Expand DownExpand Up@@ -553,8 +552,7 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 });

 return new Response(readable, { headers });
 } catch (error) {
 this.onerror?.(error as Error);
 } catch {
 return this.createJsonErrorResponse(500, -32_000, 'Error replaying events');
 }
 }
Expand DownExpand Up@@ -586,23 +584,9 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 * Handles unsupported requests (`PUT`, `PATCH`, etc.)
 */
 private handleUnsupportedRequest(): Response {
 return Response.json(
 {
 jsonrpc: '2.0',
 error: {
 code: -32_000,
 message: 'Method not allowed.'
 },
 id: null
 },
 {
 status: 405,
 headers: {
 Allow: 'GET, POST, DELETE',
 'Content-Type': 'application/json'
 }
 }
 );
 return this.createJsonErrorResponse(405, -32_000, 'Method not allowed.', {
 headers: { Allow: 'GET, POST, DELETE' }
 });
 }

 /**
Expand DownExpand Up@@ -807,8 +791,10 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 return new Response(readable, { status: 200, headers });
 } catch (error) {
 // return JSON-RPC formatted error
 this.onerror?.(error as Error);
 return this.createJsonErrorResponse(400, -32_700, 'Parse error', { data: String(error) });
 return this.createJsonErrorResponse(400, -32_700, 'Parse error', {
 data: String(error),
 cause: error instanceof Error ? error : new Error(String(error))
 });
 }
 }

Expand Down

103 changes: 103 additions & 0 deletions
packages/server/test/server/streamableHttp.test.ts

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -765,4 +765,107 @@ describe('Zod v4', () => {
 await expect(transport.start()).rejects.toThrow('Transport already started');
 });
 });

 describe('HTTPServerTransport - onerror callback', () => {
 let transport: WebStandardStreamableHTTPServerTransport;
 let errors: Error[];

 beforeEach(async () => {
 transport = new WebStandardStreamableHTTPServerTransport({
 sessionIdGenerator: () => randomUUID()
 });
 errors = [];
 transport.onerror = error => errors.push(error);
 await transport.start();
 });

 it('should call onerror for invalid Accept header on POST', async () => {
 const request = createRequest('POST', TEST_MESSAGES.initialize, { accept: 'application/json' });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(406);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Not Acceptable/);
 });

 it('should call onerror for invalid Content-Type on POST', async () => {
 const request = new Request('http://localhost/mcp', {
 method: 'POST',
 headers: {
 Accept: 'application/json, text/event-stream',
 'Content-Type': 'text/plain'
 },
 body: JSON.stringify(TEST_MESSAGES.initialize)
 });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(415);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Unsupported Media Type/);
 });

 it('should call onerror for invalid JSON on POST', async () => {
 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(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Parse error/);
 });

 it('should call onerror for invalid JSON-RPC message on POST', async () => {
 const request = new Request('http://localhost/mcp', {
 method: 'POST',
 headers: {
 Accept: 'application/json, text/event-stream',
 'Content-Type': 'application/json'
 },
 body: JSON.stringify({ not: 'a jsonrpc message' })
 });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(400);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Parse error.*Invalid JSON-RPC/);
 });

 it('should call onerror for invalid Accept header on GET', async () => {
 const request = createRequest('GET', undefined, { accept: 'application/json' });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(406);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Not Acceptable/);
 });

 it('should call onerror for unsupported HTTP methods', async () => {
 const request = new Request('http://localhost/mcp', { method: 'PUT' });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(405);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toBe('Method not allowed.');
 });

 it('should preserve original error object when createJsonErrorResponse receives cause', async () => {
 const thrown = new Error('boom-from-onmessage');
 transport.onmessage = () => {
 throw thrown;
 };

 const request = createRequest('POST', TEST_MESSAGES.initialize);
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(400);
 expect(errors.length).toBe(1);
 expect(errors[0]).toBe(thrown);
 });
 });
});
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/* Restore images, videos, iframes, canvas */
img, video, iframe, canvas, svg, picture, [style*="background-image"] {
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';
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fix: call onerror callback for all error responses in StreamableHTTPServerTransport by kdn-posipaka · Pull Request #1687 · modelcontextprotocol/typescript-sdk · GitHub
Skip to content
fix: call onerror callback for all error responses in StreamableHTTPServerTransport#1687

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kdn-posipaka
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6
commits into

from

 Closed


fix: call onerror callback for all error responses in StreamableHTTPServerTransport
#1687
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d67929f

fix: call onerror callback for all error responses in StreamableHTTPS…

Mar 16, 2026
df897d7

Add changeset for onerror callback fix

Mar 16, 2026
15514e5

fix: resolve typecheck and lint errors in streamableHttp tests

Mar 16, 2026
3a1a8b7

fix: address review feedback - handleUnsupportedRequest centralizatio…

Mar 17, 2026
30ff76b

fix: format streamableHttp.ts with prettier

Mar 17, 2026
5fcc3b1

test(server): add regression coverage for onerror unsupported-method …


Maverick-666 Mar 17, 2026

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5 changes: 5 additions & 0 deletions
.changeset/fix-silent-errors.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
"@modelcontextprotocol/sdk": patch
---

Fix silent transport errors by ensuring onerror callback is invoked for all error responses in StreamableHTTPServerTransport

34 changes: 10 additions & 24 deletions
packages/server/src/server/streamableHttp.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -284,9 +284,10 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 status: number,
 code: number,
 message: string,
 options?: { headers?: Record<string, string>; data?: string }
 options?: { headers?: Record<string, string>; data?: string; cause?: Error }
 ): Response {
 const error: { code: number; message: string; data?: string } = { code, message };
 this.onerror?.(options?.cause ?? new Error(message));
 if (options?.data !== undefined) {
 error.data = options.data;
 }
Expand DownExpand Up@@ -321,7 +322,6 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 const hostHeader = req.headers.get('host');
 if (!hostHeader || !this._allowedHosts.includes(hostHeader)) {
 const error = `Invalid Host header: ${hostHeader}`;
 this.onerror?.(new Error(error));
 return this.createJsonErrorResponse(403, -32_000, error);
 }
 }
Expand All@@ -331,7 +331,6 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 const originHeader = req.headers.get('origin');
 if (originHeader && !this._allowedOrigins.includes(originHeader)) {
 const error = `Invalid Origin header: ${originHeader}`;
 this.onerror?.(new Error(error));
 return this.createJsonErrorResponse(403, -32_000, error);
 }
 }
Expand DownExpand Up@@ -553,8 +552,7 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 });

 return new Response(readable, { headers });
 } catch (error) {
 this.onerror?.(error as Error);
 } catch {
 return this.createJsonErrorResponse(500, -32_000, 'Error replaying events');
 }
 }
Expand DownExpand Up@@ -586,23 +584,9 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 * Handles unsupported requests (`PUT`, `PATCH`, etc.)
 */
 private handleUnsupportedRequest(): Response {
 return Response.json(
 {
 jsonrpc: '2.0',
 error: {
 code: -32_000,
 message: 'Method not allowed.'
 },
 id: null
 },
 {
 status: 405,
 headers: {
 Allow: 'GET, POST, DELETE',
 'Content-Type': 'application/json'
 }
 }
 );
 return this.createJsonErrorResponse(405, -32_000, 'Method not allowed.', {
 headers: { Allow: 'GET, POST, DELETE' }
 });
 }

 /**
Expand DownExpand Up@@ -807,8 +791,10 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
 return new Response(readable, { status: 200, headers });
 } catch (error) {
 // return JSON-RPC formatted error
 this.onerror?.(error as Error);
 return this.createJsonErrorResponse(400, -32_700, 'Parse error', { data: String(error) });
 return this.createJsonErrorResponse(400, -32_700, 'Parse error', {
 data: String(error),
 cause: error instanceof Error ? error : new Error(String(error))
 });
 }
 }

Expand Down

103 changes: 103 additions & 0 deletions
packages/server/test/server/streamableHttp.test.ts

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -765,4 +765,107 @@ describe('Zod v4', () => {
 await expect(transport.start()).rejects.toThrow('Transport already started');
 });
 });

 describe('HTTPServerTransport - onerror callback', () => {
 let transport: WebStandardStreamableHTTPServerTransport;
 let errors: Error[];

 beforeEach(async () => {
 transport = new WebStandardStreamableHTTPServerTransport({
 sessionIdGenerator: () => randomUUID()
 });
 errors = [];
 transport.onerror = error => errors.push(error);
 await transport.start();
 });

 it('should call onerror for invalid Accept header on POST', async () => {
 const request = createRequest('POST', TEST_MESSAGES.initialize, { accept: 'application/json' });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(406);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Not Acceptable/);
 });

 it('should call onerror for invalid Content-Type on POST', async () => {
 const request = new Request('http://localhost/mcp', {
 method: 'POST',
 headers: {
 Accept: 'application/json, text/event-stream',
 'Content-Type': 'text/plain'
 },
 body: JSON.stringify(TEST_MESSAGES.initialize)
 });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(415);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Unsupported Media Type/);
 });

 it('should call onerror for invalid JSON on POST', async () => {
 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(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Parse error/);
 });

 it('should call onerror for invalid JSON-RPC message on POST', async () => {
 const request = new Request('http://localhost/mcp', {
 method: 'POST',
 headers: {
 Accept: 'application/json, text/event-stream',
 'Content-Type': 'application/json'
 },
 body: JSON.stringify({ not: 'a jsonrpc message' })
 });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(400);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Parse error.*Invalid JSON-RPC/);
 });

 it('should call onerror for invalid Accept header on GET', async () => {
 const request = createRequest('GET', undefined, { accept: 'application/json' });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(406);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toMatch(/Not Acceptable/);
 });

 it('should call onerror for unsupported HTTP methods', async () => {
 const request = new Request('http://localhost/mcp', { method: 'PUT' });
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(405);
 expect(errors.length).toBe(1);
 expect(errors[0]!.message).toBe('Method not allowed.');
 });

 it('should preserve original error object when createJsonErrorResponse receives cause', async () => {
 const thrown = new Error('boom-from-onmessage');
 transport.onmessage = () => {
 throw thrown;
 };

 const request = createRequest('POST', TEST_MESSAGES.initialize);
 const response = await transport.handleRequest(request);

 expect(response.status).toBe(400);
 expect(errors.length).toBe(1);
 expect(errors[0]).toBe(thrown);
 });
 });
});
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