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feat(client/sse): allow custom fetch implementation #296

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189c7dc
feat(client/sse): allow custom `fetch` implementation
NitroRCr Apr 9, 2025
5082b60
Merge branch 'modelcontextprotocol:main' into main
NitroRCr Apr 9, 2025
dc172d7
fix to pass sse test
NitroRCr Apr 9, 2025
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13 changes: 11 additions & 2 deletions src/client/sse.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,8 @@ export class SseError extends Error {
}
}

type FetchLike = (url: string | URL, init?: RequestInit) => Promise<Response>;

/**
* Configuration options for the `SSEClientTransport`.
*/
Expand Down Expand Up @@ -47,6 +49,11 @@ export type SSEClientTransportOptions = {
* Customizes recurring POST requests to the server.
*/
requestInit?: RequestInit;

/**
* Customizes the fetch implementation.
*/
fetch?: FetchLike;
};

/**
Expand All @@ -61,6 +68,7 @@ export class SSEClientTransport implements Transport {
private _eventSourceInit?: EventSourceInit;
private _requestInit?: RequestInit;
private _authProvider?: OAuthClientProvider;
private _fetch?: FetchLike;

onclose?: () => void;
onerror?: (error: Error) => void;
Expand All @@ -74,6 +82,7 @@ export class SSEClientTransport implements Transport {
this._eventSourceInit = opts?.eventSourceInit;
this._requestInit = opts?.requestInit;
this._authProvider = opts?.authProvider;
this._fetch = opts?.fetch;
}

private async _authThenStart(): Promise<void> {
Expand Down Expand Up @@ -113,7 +122,7 @@ export class SSEClientTransport implements Transport {
this._eventSource = new EventSource(
this._url.href,
this._eventSourceInit ?? {
fetch: (url, init) => this._commonHeaders().then((headers) => fetch(url, {
fetch: (url, init) => this._commonHeaders().then((headers) => (this._fetch ?? fetch)(url, {
...init,
headers: {
...headers,
Expand Down Expand Up @@ -222,7 +231,7 @@ export class SSEClientTransport implements Transport {
signal: this._abortController?.signal,
};

const response = await fetch(this._endpoint, init);
const response = await (this._fetch ?? fetch)(this._endpoint, init);
if (!response.ok) {
if (response.status === 401 && this._authProvider) {
const result = await auth(this._authProvider, { serverUrl: this._url });
Expand Down