## The normal **FastAPI** app { #the-normal-fastapi-app }

Let's first see how the normal API app would look like before adding the callback.

It will have a *path operation* that will receive an `Invoice` body, and a query parameter `callback_url` that will contain the URL for the callback.

			if contextCanceled(ctx) {
				w.WriteHeader(499)
				return
			}
			f.ServeHTTP(w, r)
		case <-r.Context().Done():
			globalHTTPStats.addRequestsInQueue(-1)
			// When the client disconnects before getting the S3 handler
			// status code response, set the status code to 499 so this request
			// will be properly audited and traced.
			w.WriteHeader(499)
		default:
			globalHTTPStats.addRequestsInQueue(-1)

        SmbFile file = new SmbFile(baseUrl + "shared/" + filename, testContext);
        file.createNewFile();
        assertTrue(file.exists(), "File should exist after creation");

        // Ensure proper cleanup before delete
        file.close();
        Thread.sleep(500); // Give more time for handle release
        System.gc(); // Force garbage collection
        Thread.sleep(200);

		return grid.NewRemoteErr(errDiskNotFound)
	}
	if params.Cache == nil {
		return grid.NewRemoteErrString("NSScannerHandler: provided cache is nil")
	}

	// Collect updates, stream them before the full cache is sent.
	updates := make(chan dataUsageEntry, 1)
	var wg sync.WaitGroup
	wg.Add(1)
	go func() {
		defer wg.Done()
		for update := range updates {
			resp := storageNSScannerRPC.NewResponse()

     * Handles encoding detection from parent URLs and configuration settings.
     *
     * @param url the URL to decode
     * @param escapePlus whether to escape plus signs before decoding
     * @return the decoded URL name, or original URL if decoding fails
     */
    default String decodeUrlAsName(final String url, final boolean escapePlus) {
        if (url == null) {
            return null;

        /** Flag indicating whether changes should be committed to the file. */
        protected boolean isCommit = false;

        /** Temporary file used for writing updates before committing. */
        protected File newFile;

        /** Writer for outputting content to the temporary file. */
        protected Writer writer;

   * optimistic retry code, relying on rechecked sets of reads.
   *
   * @param x the value
   * @param hc the hash code holder
   * @param wasUncontended false if CAS failed before call
   */
  final void retryUpdate(long x, int @Nullable [] hc, boolean wasUncontended) {
    int h;
    if (hc == null) {
      threadHashCode.set(hc = new int[1]); // Initialize randomly

        return Long.reverseBytes(bigEndian);
      }

      @Override
      public void putLongLittleEndian(byte[] array, int offset, long value) {
        // Reverse the order of the bytes before storing, since we're on big-endian hardware.
        long littleEndianValue = Long.reverseBytes(value);
        theUnsafe.putLong(array, (long) offset + BYTE_ARRAY_BASE_OFFSET, littleEndianValue);
      }
    };

     * @return true if retry should be attempted
     */
    public boolean shouldRetry(int attemptNumber) {
        return retryPolicy.shouldRetry(this, attemptNumber);
    }

    /**
     * Get the delay before next retry
     *
     * @param attemptNumber the current attempt number
     * @return delay in milliseconds
     */
    public long getRetryDelayMs(int attemptNumber) {

                    maxDate = start.clone().add(this.maxSpan);
                if (maxDate && end.isAfter(maxDate))
                    end = maxDate.clone();

                // If the end of the range is before the minimum or the start of the range is
                // after the maximum, don't display this range option at all.
                if ((this.minDate && end.isBefore(this.minDate, this.timepicker ? 'minute' : 'day'))