feat(mcp): allow custom fetch for HTTP and SSE transports#14134
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aayush-kapoor merged 5 commits intoApr 6, 2026
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Adds an optional `fetch` option to `MCPTransportConfig` (and both `HttpMCPTransport` / `SseMCPTransport` constructors) so callers can supply a request-local fetch instead of relying on `globalThis.fetch`. The custom fetch is also forwarded to OAuth `auth()` calls so token discovery and exchange use the same fetch implementation. Fixes runtimes where self-fetches are blocked (e.g. Cloudflare Workers error 1042 on same-worker MCP routes with Nitro). Closes vercel#13449
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…14159) This is an automated backport of #14134 to the release-v6.0 branch. FYI @jaydeep-pipaliya This backport has conflicts that need to be resolved manually. ### `git cherry-pick` output ``` Auto-merging packages/mcp/src/tool/mcp-http-transport.test.ts Auto-merging packages/mcp/src/tool/mcp-http-transport.ts CONFLICT (content): Merge conflict in packages/mcp/src/tool/mcp-http-transport.ts Auto-merging packages/mcp/src/tool/mcp-sse-transport.test.ts Auto-merging packages/mcp/src/tool/mcp-sse-transport.ts CONFLICT (content): Merge conflict in packages/mcp/src/tool/mcp-sse-transport.ts Auto-merging packages/mcp/src/tool/mcp-transport.ts error: could not apply a00d1d3... feat(mcp): allow custom fetch for HTTP and SSE transports (#14134) hint: After resolving the conflicts, mark them with hint: "git add/rm <pathspec>", then run hint: "git cherry-pick --continue". hint: You can instead skip this commit with "git cherry-pick --skip". hint: To abort and get back to the state before "git cherry-pick", hint: run "git cherry-pick --abort". hint: Disable this message with "git config set advice.mergeConflict false" ``` --------- Co-authored-by: Jaydeep pipaliya <71074587+jaydeep-pipaliya@users.noreply.github.com> Co-authored-by: Aayush Kapoor <aayushkapoor34@gmail.com>
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Summary
Fixes #13449.
@ai-sdk/mcphardcodedglobalThis.fetchin its HTTP and SSE transports, breaking same-app MCP calls on runtimes that block self-fetches (e.g. Cloudflare Workers error1042via Nitro).fetchfield toMCPTransportConfigand bothHttpMCPTransport/SseMCPTransportconstructorsglobalThis.fetchwhen not provided (no breaking change)auth()calls so token discovery/exchange uses the same fetch implementationhttpandssetransport types as requested in the issueUsage:
Test plan
describe('custom fetch', ...)tests to bothmcp-http-transport.test.tsandmcp-sse-transport.test.tsverifying the custom fetch function is called for GET (start) and POST (send) operationspnpm test:node)pnpm buildinpackages/mcp)