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Merge pull request #1946 from modelcontextprotocol/v2/fix/firefox-sse-stream-hang

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fix: prime SSE streams so Firefox resolves the events fetch
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Cliff Hall 2026-08-11 11:22:34 -04:00 • committed by GitHub
commit 9e074aa6f2
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1 changed files with 282 additions and 1 deletions
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19
core/react/useServers.ts
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@ -82,6 +82,18 @@ async function readErrorMessage(res: Response): Promise<string> {
return `HTTP ${res.status}`;
}
/**
* Whether an SSE frame carries an actual event rather than only comment
* lines. The backend primes each stream with an inert `:` comment so a
* streaming `fetch()` resolves on Firefox at all (#1858); that frame must
* not be mistaken for a change notification.
*/
function isSseDataFrame(frame: string): boolean {
return frame
.split("\n")
.some((line) => line.startsWith("event:") || line.startsWith("data:"));
}
export function useServers(opts: UseServersOptions): UseServersResult {
const { baseUrl, authToken, fetchFn } = opts;
const doFetch = fetchFn ?? globalThis.fetch;
@ -157,6 +169,10 @@ export function useServers(opts: UseServersOptions): UseServersResult {
// single background refresh per decode chunk. Two `change`
// broadcasts landing in the same chunk become one re-fetch instead
// of two concurrent ones whose setState order is unspecified.
// Frames carrying no `event:`/`data:` field are skipped: the backend
// opens the stream with an inert `:` comment frame so Firefox
// resolves this fetch at all (see SSE_PRIMING_COMMENT in the remote
// server), and that must not read as a change.
// Cross-chunk debounce is not added: `awaitWriteFinish`'s 100ms
// stability threshold already serializes external edits at the
// source, and chained fetches against the same GET endpoint are
@ -169,8 +185,9 @@ export function useServers(opts: UseServersOptions): UseServersResult {
let sawFrame = false;
let frameEnd = buffer.indexOf("\n\n");
while (frameEnd !== -1) {
const frame = buffer.slice(0, frameEnd);
buffer = buffer.slice(frameEnd + 2);
sawFrame = true;
if (isSseDataFrame(frame)) sawFrame = true;
frameEnd = buffer.indexOf("\n\n");
}
if (sawFrame) void refreshInternal(true);