## 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.

This part is pretty normal, most of the code is probably already familiar to you:

```Python hl_lines="9-13  36-53"
{!../../../docs_src/openapi_callbacks/tutorial001.py!}
```

!!! tip

    teststring = newTestString(new Random(1), bitSet, percentMatching);
  }

  @Benchmark
  public int countIn(int reps) {
    int result = 0;
    CharMatcher matcher = this.matcher;
    String teststring = this.teststring;
    for (int i = 0; i < reps; i++) {
      result += matcher.countIn(teststring);
    }
    return result;
  }

  @Benchmark
  public int collapseFrom(int reps) {
    int result = 0;

		// Setting `prefix` to contain the object name as its prefix (Test number 23).
		{bucketNames[0], "min", "", "", "", 2, listMultipartResults[10], nil, true},
		// Setting `prefix` to contain the object name as its prefix (Test number 24).
		{bucketNames[0], "min", "", "", "", 1, listMultipartResults[11], nil, true},
		// Setting `prefix` to not to contain the object name as its prefix (Test number 25-26).

Let's say you have a *path operation* with a path `/files/{file_path}`.

But you need `file_path` itself to contain a *path*, like `home/johndoe/myfile.txt`.

So, the URL for that file would be something like: `/files/home/johndoe/myfile.txt`.

### OpenAPI support

OpenAPI doesn't support a way to declare a *path parameter* to contain a *path* inside, as that could lead to scenarios that are difficult to test and define.

      put(nullKeyEntry);
      fail("put(null, value) should throw");
    } catch (NullPointerException expected) {
    }
    expectUnchanged();
    expectNullKeyMissingWhenNullKeysUnsupported(
        "Should not contain null key after unsupported put(null, value)");
  }

  @MapFeature.Require({SUPPORTS_PUT, ALLOWS_NULL_VALUES})
  public void testPut_nullValueSupported() {

        Map artifactMap = project.getArtifactMap();

        assertNotNull( artifactMap, "artifact-map should not be null." );
        assertEquals( 1, artifactMap.size(), "artifact-map should contain 1 element." );

        Artifact artifact = (Artifact) artifactMap.get( key );

        assertNotNull( artifact, "dependency artifact not found in map." );

  // stomped by the controller.
  // +optional
  optional AggregationRule aggregationRule = 3;
}

// ClusterRoleBinding references a ClusterRole, but not contain it.  It can reference a ClusterRole in the global namespace,
// and adds who information via Subject.
// Deprecated in v1.17 in favor of rbac.authorization.k8s.io/v1 ClusterRoleBinding, and will no longer be served in v1.22.

  // stomped by the controller.
  // +optional
  optional AggregationRule aggregationRule = 3;
}

// ClusterRoleBinding references a ClusterRole, but not contain it.  It can reference a ClusterRole in the global namespace,
// and adds who information via Subject.
// Deprecated in v1.17 in favor of rbac.authorization.k8s.io/v1 ClusterRoleBinding, and will no longer be served in v1.22.

	_, ok := h[xhttp.AmzServerSideEncryption]
	// Return only true if the SSE header is specified and does not contain the SSE-KMS value
	return ok && !strings.EqualFold(h.Get(xhttp.AmzServerSideEncryption), xhttp.AmzEncryptionKMS)
}

// ParseHTTP parses the SSE-S3 related HTTP headers and checks
// whether they contain valid values.
func (sses3) ParseHTTP(h http.Header) error {

    assertEquals("", matcher.removeFrom(""));
    assertEquals("", matcher.replaceFrom("", 'z'));
    assertEquals("", matcher.replaceFrom("", "ZZ"));
    assertEquals("", matcher.trimFrom(""));
    assertEquals(0, matcher.countIn(""));
  }

  @J2ktIncompatible
  @GwtIncompatible // NullPointerTester
  private static void doTestNull(CharMatcher matcher) throws Exception {
    NullPointerTester tester = new NullPointerTester();