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fix: use RequestInit['headers'] in normalizeHeaders #3129

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fix: use RequestInit['headers'] in normalizeHeaders #3129

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c2dae37
fix: use RequestInit['headers'] in normalizeHeaders
theOguz16 Oct 29, 2026
9cfb5d7
docs: drop the DOM-only HeadersInit name from the normalizeHeaders do…
theOguz16 Oct 29, 2026
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10 changes: 10 additions & 0 deletions .changeset/normalize-headers-node-only-consumers.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,10 @@
---
'@modelcontextprotocol/sdk': patch
---

Reference `RequestInit['headers']` instead of the bare global `HeadersInit` in `normalizeHeaders`.

`HeadersInit` is declared by the DOM lib only, while `RequestInit` is also provided globally by `@types/node` through `undici-types`. Consumers that compile the SDK with `"lib": ["ES2023"]`, `"types": ["node"]` and `"skipLibCheck": false` therefore failed with
`TS2304: Cannot find name 'HeadersInit'` on `dist/{esm,cjs}/shared/transport.d.ts`.

This matches the signature already used on `main`, and resolves the v1 line of the report.
4 changes: 2 additions & 2 deletions src/shared/transport.ts
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Expand Up @@ -3,10 +3,10 @@ import { JSONRPCMessage, MessageExtraInfo, RequestId } from '../types.js';
export type FetchLike = (url: string | URL, init?: RequestInit) => Promise<Response>;

/**
* Normalizes HeadersInit to a plain Record<string, string> for manipulation.
* Normalizes RequestInit['headers'] to a plain Record<string, string> for manipulation.
* Handles Headers objects, arrays of tuples, and plain objects.
*/
export function normalizeHeaders(headers: HeadersInit | undefined): Record<string, string> {
export function normalizeHeaders(headers: RequestInit['headers'] | undefined): Record<string, string> {
if (!headers) return {};

if (headers instanceof Headers) {
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