fix: stop XHR retries once the request is aborted - #470

Why

getXHRRetryHook schedules a re-send after a retryable status (429/500/502/503/504). If the caller cancels the request while a retry is waiting, the timer still fires: it calls request.open() and send() again and downloads data nobody needs. This matters for tile loading, where Viv/deck.gl aborts tiles that scroll out of view while panning. The hook had no way to know about the abort.

Related: ImagingDataCommons/dicom-microscopy-viewer#312 and ImagingDataCommons/dicom-microscopy-viewer#313 (headless tile reader with AbortSignal support).

What

dicomweb-client is getting a request.signal option. When it is set, request hooks receive the signal as metadata.signal. The retry hook now honors that signal:

• a request whose signal is already aborted is not sent;
• aborting while a retry is scheduled cancels it (operation.stop()), so there's no re-open and no re-send;
• a retryable response that arrives after the abort is passed on to the client handler instead of being retried;
• the abort listener is removed once the request finishes.

Without a signal, the hook behaves exactly as before. signal?: AbortSignal is added to DICOMwebClientRequestHookMetadata in AppConfig.d.ts.

Merging is safe on its own. It takes effect once the dicomweb-client version with request.signal is released and Slim uses it (dcmjs-org/dicomweb-client#144). With today's dicomweb-client, metadata.signal is never set, so nothing changes.

Testing

• The existing 7 tests in src/utils/__tests__/xhrRetryHook.test.ts are unchanged and passing.

• 4 new tests cover:

  • abort while a retry is scheduled (no re-send, no re-open);
  • a response arriving after the abort (not retried, passed on once);
  • a signal that's already aborted (not sent);
  • listener cleanup.

  All 4 fail against the previous hook.

• Full suite: 177 passed. tsc --noEmit and biome are clean.