## 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

// PolicyRule holds information that describes a policy rule, but does not contain information
// about who the rule applies to or which namespace the rule applies to.
message PolicyRule {
  // Verbs is a list of Verbs that apply to ALL the ResourceKinds contained in this rule. '*' represents all verbs.
  repeated string verbs = 1;

| `contact` | `dict` | The contact information for the exposed API. It can contain several fields. <details><summary><code>contact</code> fields</summary><table><thead><tr><th>Parameter</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code>name</code></td><td><code>str</code></td><td>The identifying name of the contact person/organization.</td></tr><tr><td><code>url</code></td><td><code>str</code></td><td>The...

      if (first) {
        firstIsRandalcat = codePoint in randalcatSet
      } else if (firstIsRandalcat) {
        // 'If a string contains any RandALCat character, the string MUST NOT contain any LCat
        // character.'
        if (codePoint in lcatSet) return null

        // 'If a string contains any RandALCat character, a RandALCat character MUST be the last
        // character of the string.'

#   and scripts on Linux create a persistent container called "tf"
#   which mounts your TensorFlow directory into the container.
#
#   Important: because the container is persistent, you cannot change TFCI
#   variables in between script executions. To forcibly remove the
#   container and start fresh, run "docker rm -f tf". Removing the container
#   destroys some temporary bazel data and causes longer builds.
#

        append(request.url)
      } else {
        append(requestPath(request.url))
      }
      append(" HTTP/1.1")
    }

  /**
   * Returns true if the request line should contain the full URL with host and port (like "GET
   * http://android.com/foo HTTP/1.1") or only the path (like "GET /foo HTTP/1.1").
   */
  private fun includeAuthorityInRequestLine(
    request: Request,

                    analyze(inlineFunction)
                }
            }
            analyzedElements.addAll(nextInlineFunctions)
        }
    }

    /**
     * Returns the list of files that contain all reached inline functions.
     */
    fun allFiles(): List<KtFile> = analyzedElements.mapTo(mutableSetOf()) { it.containingKtFile }.toList()

    /**

// PolicyRule holds information that describes a policy rule, but does not contain information
// about who the rule applies to or which namespace the rule applies to.
message PolicyRule {
  // Verbs is a list of Verbs that apply to ALL the ResourceKinds contained in this rule. '*' represents all verbs.
  repeated string verbs = 1;

// PolicyRule holds information that describes a policy rule, but does not contain information
// about who the rule applies to or which namespace the rule applies to.
message PolicyRule {
  // Verbs is a list of Verbs that apply to ALL the ResourceKinds contained in this rule. '*' represents all verbs.
  repeated string verbs = 1;

The new [ParseCookie] function parses a Cookie header value and
returns all the cookies which were set in it. Since the same cookie
name can appear multiple times the returned Values can contain
more than one value for a given key.

The new [ParseSetCookie] function parses a Set-Cookie header value and