mu := PaddedMutex{NewDRWMutex(ds, "")}
		for pb.Next() {
			mu.Lock(id, source)
			mu.Unlock(b.Context())
		}
	})
}

func benchmarkMutex(b *testing.B, slack, work bool) {
	b.ResetTimer()
	b.ReportAllocs()

	mu := NewDRWMutex(ds, "")
	if slack {
		b.SetParallelism(10)
	}
	b.RunParallel(func(pb *testing.PB) {
		foo := 0
		for pb.Next() {
			mu.Lock(id, source)
			mu.Unlock(b.Context())

        responseData.setCharSet("ISO-8859-1");
        responseData.setMimeType("text/html");
        final ResultData resultData = htmlTransformer.transform(responseData);
        assertEquals(content, new String(resultData.getData()));
        assertEquals(1, resultData.getChildUrlSet().size());
        assertEquals("http://hoge/test2.html", resultData.getChildUrlSet().iterator().next().getUrl());
    }

    public void test_transform_urllink() {

      try {
        in.close();
      } finally {
        in = null;
      }
    }
  }

  /** Closes the current input stream and opens the next one, if any. */
  private void advance() throws IOException {
    close();
    if (it.hasNext()) {
      in = it.next().openStream();
    }
  }

  @Override
  public int available() throws IOException {
    if (in == null) {
      return 0;
    }

///

/// info

In this example we use invented custom headers `X-Key` and `X-Token`.

But in real cases, when implementing security, you would get more benefits from using the integrated [Security utilities (the next chapter)](../security/index.md){.internal-link target=_blank}.

///

## Dependencies errors and return values { #dependencies-errors-and-return-values }

You can use the same dependency *functions* you use normally.

    checkNotNull(appendable);
    if (parts.hasNext()) {
      appendable.append(toString(parts.next()));
      while (parts.hasNext()) {
        appendable.append(separator);
        appendable.append(toString(parts.next()));
      }
    }
    return appendable;
  }

  /**

   * }
   *
   * <p><b>Note:</b> This method <i>may</i> work with certain non-ASCII text but is not safe for use
   * with arbitrary Unicode text. It is mostly intended for use with text that is known to be safe
   * for use with it (such as all-ASCII text) and for simple debugging text. When using this method,
   * consider the following:
   *
   * <ul>
   *   <li>it may split surrogate pairs

): List<T> {
  val ia = a.iterator()
  val ib = b.iterator()

  return buildList {
    while (ia.hasNext() || ib.hasNext()) {
      if (ia.hasNext()) {
        add(ia.next())
      }
      if (ib.hasNext()) {
        add(ib.next())
      }
    }
  }

The only new thing is the `callbacks=invoices_callback_router.routes` as an argument to the *path operation decorator*. We'll see what that is next.

## Documenting the callback { #documenting-the-callback }

The actual callback code will depend heavily on your own API app.

And it will probably vary a lot from one app to the next.

It could be just one or two lines of code, like:

```Python
callback_url = "https://example.com/api/v1/invoices/events/"

      @Override
      public boolean hasNext() {
        return entryItr.hasNext();
      }

      @Override
      public V next() {
        return entryItr.next().getValue();
      }
    };
  }

  @Override
  public boolean contains(@Nullable Object object) {
    return object != null && Iterators.contains(iterator(), object);
  }

  @Override

        return doMove(form, -1);
    }

    /**
     * Navigates to the next page of search results.
     *
     * @param form the list form containing current search criteria
     * @return HTML response with next page results
     */
    @Execute
    @Secured({ ROLE, ROLE + VIEW })
    public HtmlResponse next(final ListForm form) {
        saveToken();
        return doMove(form, 1);
    }