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jaydeep-pipaliyavercel-ai-sdk[bot]
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Backport conflicts for PR #14134 to release-v6.0
1 parent c3a057d commit a1ee4bd

6 files changed

Lines changed: 169 additions & 5 deletions

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‎.changeset/friendly-mugs-smell.md‎

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---
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"@ai-sdk/mcp": patch
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---
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feat(mcp): allow custom fetch for HTTP and SSE transports

‎packages/mcp/src/tool/mcp-http-transport.test.ts‎

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@@ -427,4 +427,62 @@ describe('HttpMCPTransport', () => {
427427
fetchSpy.mockRestore();
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});
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});
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describe('custom fetch', () => {
432+
it('should use provided fetch function instead of globalThis.fetch', async () => {
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const customFetch = vi.fn(globalThis.fetch);
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435+
transport = new HttpMCPTransport({
436+
url: 'http://localhost:4000/mcp',
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fetch: customFetch,
438+
});
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server.urls['http://localhost:4000/mcp'].response = {
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type: 'error',
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status: 405,
443+
};
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await transport.start();
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await vi.waitFor(() => {
448+
expect(customFetch).toHaveBeenCalled();
449+
});
450+
451+
expect(customFetch).toHaveBeenCalledWith(
452+
'http://localhost:4000/mcp',
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expect.objectContaining({ method: 'GET' }),
454+
);
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});
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457+
it('should use provided fetch function for POST send()', async () => {
458+
const customFetch = vi.fn(globalThis.fetch);
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transport = new HttpMCPTransport({
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url: 'http://localhost:4000/mcp',
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fetch: customFetch,
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});
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server.urls['http://localhost:4000/mcp'].response = {
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type: 'json-value',
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body: { jsonrpc: '2.0', id: 1, result: { ok: true } },
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headers: { 'mcp-session-id': 'abc123' },
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};
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await transport.start();
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const message = {
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jsonrpc: '2.0' as const,
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method: 'initialize',
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id: 1,
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params: {},
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};
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await transport.send(message);
481+
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expect(customFetch).toHaveBeenCalledWith(
483+
'http://localhost:4000/mcp',
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expect.objectContaining({ method: 'POST' }),
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);
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});
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});
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});

‎packages/mcp/src/tool/mcp-http-transport.ts‎

Lines changed: 14 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,6 @@
11
import {
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EventSourceParserStream,
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FetchFunction,
34
withUserAgentSuffix,
45
getRuntimeEnvironmentUserAgent,
56
} from '@ai-sdk/provider-utils';
@@ -31,6 +32,7 @@ export class HttpMCPTransport implements MCPTransport {
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private sessionId?: string;
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private inboundSseConnection?: { close: () => void };
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private redirectMode: RequestRedirect;
35+
private fetchFn: FetchFunction;
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// Inbound SSE resumption and reconnection state
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private lastInboundEventId?: string;
@@ -50,17 +52,24 @@ export class HttpMCPTransport implements MCPTransport {
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url,
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headers,
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authProvider,
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<<<<<<< HEAD
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redirect = 'follow',
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=======
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redirect = 'error',
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fetch: fetchFn,
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>>>>>>> a00d1d3f9 (feat(mcp): allow custom fetch for HTTP and SSE transports (#14134))
5461
}: {
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url: string;
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headers?: Record<string, string>;
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authProvider?: OAuthClientProvider;
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redirect?: 'follow' | 'error';
66+
fetch?: FetchFunction;
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}) {
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this.url = new URL(url);
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this.headers = headers;
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this.authProvider = authProvider;
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this.redirectMode = redirect;
72+
this.fetchFn = fetchFn ?? globalThis.fetch;
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}
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private async commonHeaders(
@@ -111,7 +120,7 @@ export class HttpMCPTransport implements MCPTransport {
111120
!this.abortController.signal.aborted
112121
) {
113122
const headers = await this.commonHeaders({});
114-
await fetch(this.url, {
123+
await this.fetchFn(this.url.href, {
115124
method: 'DELETE',
116125
headers,
117126
signal: this.abortController.signal,
@@ -140,7 +149,7 @@ export class HttpMCPTransport implements MCPTransport {
140149
redirect: this.redirectMode,
141150
} satisfies RequestInit;
142151

143-
const response = await fetch(this.url, init);
152+
const response = await this.fetchFn(this.url.href, init);
144153

145154
const sessionId = response.headers.get('mcp-session-id');
146155
if (sessionId) {
@@ -153,6 +162,7 @@ export class HttpMCPTransport implements MCPTransport {
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const result = await auth(this.authProvider, {
154163
serverUrl: this.url,
155164
resourceMetadataUrl: this.resourceMetadataUrl,
165+
fetchFn: this.fetchFn,
156166
});
157167
if (result !== 'AUTHORIZED') {
158168
const error = new UnauthorizedError();
@@ -314,7 +324,7 @@ export class HttpMCPTransport implements MCPTransport {
314324
headers['last-event-id'] = resumeToken;
315325
}
316326

317-
const response = await fetch(this.url.href, {
327+
const response = await this.fetchFn(this.url.href, {
318328
method: 'GET',
319329
headers,
320330
signal: this.abortController?.signal,
@@ -332,6 +342,7 @@ export class HttpMCPTransport implements MCPTransport {
332342
const result = await auth(this.authProvider, {
333343
serverUrl: this.url,
334344
resourceMetadataUrl: this.resourceMetadataUrl,
345+
fetchFn: this.fetchFn,
335346
});
336347
if (result !== 'AUTHORIZED') {
337348
const error = new UnauthorizedError();

‎packages/mcp/src/tool/mcp-sse-transport.test.ts‎

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Original file line numberDiff line numberDiff line change
@@ -381,4 +381,75 @@ describe('SseMCPTransport', () => {
381381
fetchSpy.mockRestore();
382382
});
383383
});
384+
385+
describe('custom fetch', () => {
386+
it('should use provided fetch function for SSE connection', async () => {
387+
const controller = new TestResponseController();
388+
server.urls['http://localhost:3000/sse'].response = {
389+
type: 'controlled-stream',
390+
controller,
391+
};
392+
393+
const customFetch = vi.fn(globalThis.fetch);
394+
395+
transport = new SseMCPTransport({
396+
url: 'http://localhost:3000/sse',
397+
fetch: customFetch,
398+
});
399+
400+
const connectPromise = transport.start();
401+
controller.write(
402+
'event: endpoint\ndata: http://localhost:3000/messages\n\n',
403+
);
404+
await connectPromise;
405+
406+
expect(customFetch).toHaveBeenCalledWith(
407+
'http://localhost:3000/sse',
408+
expect.objectContaining({ headers: expect.anything() }),
409+
);
410+
411+
await transport.close();
412+
});
413+
414+
it('should use provided fetch function for POST send()', async () => {
415+
const controller = new TestResponseController();
416+
server.urls['http://localhost:3000/sse'].response = {
417+
type: 'controlled-stream',
418+
controller,
419+
};
420+
server.urls['http://localhost:3000/messages'].response = {
421+
type: 'empty',
422+
status: 200,
423+
};
424+
425+
const customFetch = vi.fn(globalThis.fetch);
426+
427+
transport = new SseMCPTransport({
428+
url: 'http://localhost:3000/sse',
429+
fetch: customFetch,
430+
});
431+
432+
const connectPromise = transport.start();
433+
controller.write(
434+
'event: endpoint\ndata: http://localhost:3000/messages\n\n',
435+
);
436+
await connectPromise;
437+
438+
customFetch.mockClear();
439+
440+
await transport.send({
441+
jsonrpc: '2.0' as const,
442+
method: 'test',
443+
params: {},
444+
id: '1',
445+
});
446+
447+
expect(customFetch).toHaveBeenCalledWith(
448+
'http://localhost:3000/messages',
449+
expect.objectContaining({ method: 'POST' }),
450+
);
451+
452+
await transport.close();
453+
});
454+
});
384455
});

‎packages/mcp/src/tool/mcp-sse-transport.ts‎

Lines changed: 13 additions & 2 deletions
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@@ -1,5 +1,6 @@
11
import {
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EventSourceParserStream,
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FetchFunction,
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withUserAgentSuffix,
45
getRuntimeEnvironmentUserAgent,
56
} from '@ai-sdk/provider-utils';
@@ -27,6 +28,7 @@ export class SseMCPTransport implements MCPTransport {
2728
private authProvider?: OAuthClientProvider;
2829
private resourceMetadataUrl?: URL;
2930
private redirectMode: RequestRedirect;
31+
private fetchFn: FetchFunction;
3032

3133
onclose?: () => void;
3234
onerror?: (error: unknown) => void;
@@ -36,17 +38,24 @@ export class SseMCPTransport implements MCPTransport {
3638
url,
3739
headers,
3840
authProvider,
41+
<<<<<<< HEAD
3942
redirect = 'follow',
43+
=======
44+
redirect = 'error',
45+
fetch: fetchFn,
46+
>>>>>>> a00d1d3f9 (feat(mcp): allow custom fetch for HTTP and SSE transports (#14134))
4047
}: {
4148
url: string;
4249
headers?: Record<string, string>;
4350
authProvider?: OAuthClientProvider;
4451
redirect?: 'follow' | 'error';
52+
fetch?: FetchFunction;
4553
}) {
4654
this.url = new URL(url);
4755
this.headers = headers;
4856
this.authProvider = authProvider;
4957
this.redirectMode = redirect;
58+
this.fetchFn = fetchFn ?? globalThis.fetch;
5059
}
5160

5261
private async commonHeaders(
@@ -85,7 +94,7 @@ export class SseMCPTransport implements MCPTransport {
8594
const headers = await this.commonHeaders({
8695
Accept: 'text/event-stream',
8796
});
88-
const response = await fetch(this.url.href, {
97+
const response = await this.fetchFn(this.url.href, {
8998
headers,
9099
signal: this.abortController?.signal,
91100
redirect: this.redirectMode,
@@ -97,6 +106,7 @@ export class SseMCPTransport implements MCPTransport {
97106
const result = await auth(this.authProvider, {
98107
serverUrl: this.url,
99108
resourceMetadataUrl: this.resourceMetadataUrl,
109+
fetchFn: this.fetchFn,
100110
});
101111
if (result !== 'AUTHORIZED') {
102112
const error = new UnauthorizedError();
@@ -235,14 +245,15 @@ export class SseMCPTransport implements MCPTransport {
235245
redirect: this.redirectMode,
236246
};
237247

238-
const response = await fetch(endpoint, init);
248+
const response = await this.fetchFn(endpoint.href, init);
239249

240250
if (response.status === 401 && this.authProvider && !triedAuth) {
241251
this.resourceMetadataUrl = extractResourceMetadataUrl(response);
242252
try {
243253
const result = await auth(this.authProvider, {
244254
serverUrl: this.url,
245255
resourceMetadataUrl: this.resourceMetadataUrl,
256+
fetchFn: this.fetchFn,
246257
});
247258
if (result !== 'AUTHORIZED') {
248259
const error = new UnauthorizedError();

‎packages/mcp/src/tool/mcp-transport.ts‎

Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1,3 +1,4 @@
1+
import { FetchFunction } from '@ai-sdk/provider-utils';
12
import { MCPClientError } from '../error/mcp-client-error';
23
import { JSONRPCMessage } from './json-rpc-message';
34
import { SseMCPTransport } from './mcp-sse-transport';
@@ -66,6 +67,13 @@ export type MCPTransportConfig = {
6667
* @default 'follow'
6768
*/
6869
redirect?: 'follow' | 'error';
70+
71+
/**
72+
* Optional custom fetch implementation to use for HTTP requests.
73+
* Useful for runtimes that need a request-local fetch.
74+
* @default globalThis.fetch
75+
*/
76+
fetch?: FetchFunction;
6977
};
7078

7179
export function createMcpTransport(config: MCPTransportConfig): MCPTransport {

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