## 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

import java.util.Collection;
import java.util.List;
import java.util.Map;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * To be implemented by test generators of things that can contain elements. Such things include
 * both {@link Collection} and {@link Map}; since there isn't an established collective noun that
 * encompasses both of these, 'container' is used.
 *
 * @author George van den Driessche
 */

    private void assertContains(VersionRange range, String version) {
        assertTrue(range.contains(newVersion(version)), range + " should contain " + version);
    }

    private void assertNotContains(VersionRange range, String version) {
        assertFalse(range.contains(newVersion(version)), range + " should not contain " + version);
    }

    @Test
    void testLowerBoundInclusiveUpperBoundInclusive() {

    assertThrows(NullPointerException.class, () -> getMap().putIfAbsent(null, v3()));
    expectUnchanged();
    expectNullKeyMissingWhenNullKeysUnsupported(
        "Should not contain null key after unsupported putIfAbsent(null, value)");
  }

  @MapFeature.Require(value = SUPPORTS_PUT, absent = ALLOWS_NULL_VALUES)
  public void testPutIfAbsent_nullValueUnsupportedAndKeyAbsent() {

        if (!table) {
            throw new RuntimeException("Section '$title' does not contain a <table> element.")
        }
        if (!table.thead[0]) {
            throw new RuntimeException("Table '$title' does not contain a <thead> element.")
        }
        if (!table.thead[0].tr[0]) {
            throw new RuntimeException("Table '$title' does not contain a <thead>/<tr> element.")
        }
        return table
    }

This directory is intended to contain Hazelcast [1] JARs for Maven Resolver Named Locks using Hazelcast.

See here [2] on how to add necessary JARs.

[1] https://github.com/hazelcast/hazelcast

</dependencies>
    ]]></configuration>
    <description>
      <![CDATA[
      This is a set of Artifact instances resolved from the set of dependencies for
      the current project.

      NOTE: This will likely contain much more than the direct dependencies of the
      current POM, since Maven uses transitive, or chained, dependency resolution.
    ]]></description>
  </expression>
  <expression>
    <syntax>project.parentArtifact</syntax>

  }

  protected void expectMissingKeys(K... elements) {
    for (K element : elements) {
      assertFalse("Should not contain key " + element, getMap().containsKey(element));
    }
  }

  protected void expectMissingValues(V... elements) {
    for (V element : elements) {
      assertFalse("Should not contain value " + element, getMap().containsValue(element));
    }
  }

      BiMap<V, K> inv = getMap().inverse();
      assertFalse(
          "Inverse should not contain entry " + reversed, inv.entrySet().contains(reversed));
      assertFalse(
          "Inverse should not contain key " + reversed.getKey(),
          inv.containsKey(reversed.getKey()));
      assertFalse(
          "Inverse should not contain value " + reversed.getValue(),
          inv.containsValue(reversed.getValue()));
      /*

	buf.Write([]byte{0, 7})
	buf.WriteString("Records")

	fmt.Println(buf.Bytes())
}

// Continuation Message
// ====================
// Header specification
// --------------------
// Continuation messages contain two headers, as follows:
// https://docs.aws.amazon.com/AmazonS3/latest/API/images/s3select-frame-diagram-cont.png
//
// Payload specification
// ---------------------
// Continuation messages have no payload.