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A new updateHeadersInPlace function *mutates* the original header object instead of replacing it. This ensures that transports holding a static reference, like SSEClientTransport, always see the latest headers.

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* In `src/server/index.ts`,
  - Added `updateHeadersInPlace` helper function to solve the stale header reference issue in `SSEClientTransport`. It mutates the header object in-place, ensuring the transport sees all updates, while carefully preserving the original `Accept` header required by the transport.
  - in `/mcp GET`, `/mcp POST`, and `/message POST`, use `updateHeadersInPlace` to replace current headers with new headers, retaining the Accept header.
This commit is contained in:
cliffhall 2025-09-06 15:51:43 -04:00
commit 2f420c4edf
1 changed files with 37 additions and 3 deletions
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40
server/src/index.ts
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@ -93,6 +93,31 @@ const getHttpHeaders = (req: express.Request): Record<string, string> => {
return headers;
};
/**
* Updates a headers object in-place, preserving the original Accept header.
* This is necessary to ensure that transports holding a reference to the headers
* object see the updates.
* @param currentHeaders The headers object to update.
* @param newHeaders The new headers to apply.
*/
const updateHeadersInPlace = (
currentHeaders: Record<string, string>,
newHeaders: Record<string, string>,
) => {
// Preserve the Accept header, which is set at transport creation and
// is not present in subsequent client requests.
const accept = currentHeaders["Accept"];
// Clear the old headers and apply the new ones.
Object.keys(currentHeaders).forEach((key) => delete currentHeaders[key]);
Object.assign(currentHeaders, newHeaders);
// Restore the Accept header.
if (accept) {
currentHeaders["Accept"] = accept;
}
};
const app = express();
app.use(cors());
app.use((req, res, next) => {
@ -292,7 +317,10 @@ app.get(
const headerHolder = sessionHeaderHolders.get(sessionId);
if (headerHolder) {
headerHolder.headers = getHttpHeaders(req);
updateHeadersInPlace(
headerHolder.headers as Record<string, string>,
getHttpHeaders(req),
);
}
try {
@ -323,7 +351,10 @@ app.post(
console.log(`Received POST message for sessionId ${sessionId}`);
const headerHolder = sessionHeaderHolders.get(sessionId);
if (headerHolder) {
headerHolder.headers = getHttpHeaders(req);
updateHeadersInPlace(
headerHolder.headers as Record<string, string>,
getHttpHeaders(req),
);
}
try {
@ -598,7 +629,10 @@ app.post(
const headerHolder = sessionHeaderHolders.get(sessionId);
if (headerHolder) {
headerHolder.headers = getHttpHeaders(req);
updateHeadersInPlace(
headerHolder.headers as Record<string, string>,
getHttpHeaders(req),
);
}
const transport = webAppTransports.get(sessionId) as SSEServerTransport;