To create the callback *path operation* use the same `APIRouter` you created above.

It should look just like a normal FastAPI *path operation*:

* It should probably have a declaration of the body it should receive, e.g. `body: InvoiceEvent`.
* And it could also have a declaration of the response it should return, e.g. `response_model=InvoiceEventReceived`.

```Python hl_lines="16-18  21-22  28-32"

  // This field cannot be empty for new Events and it can have at most 128 characters.
  optional string reportingInstance = 5;

  // action is what action was taken/failed regarding to the regarding object. It is machine-readable.
  // This field cannot be empty for new Events and it can have at most 128 characters.
  optional string action = 6;

  // reason is why the action was taken. It is human-readable.

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        ianaSuites.fromJavaName(it.javaName)
      },
    supported =
      ConnectionSpec.COMPATIBLE_TLS.cipherSuites!!.map {
        ianaSuites.fromJavaName(it.javaName)
      },
  )
}

fun historicOkHttp(version: String): Client {
  val enabled =
    FileSystem.RESOURCES.read("okhttp_$version.txt".toPath()) {
      this.readUtf8().lines().filter { it.isNotBlank() }.map {

def currentDistroJars = currentClasspath.filter { it.name.startsWith('gradle-') && it.name.endsWith('.jar') }
def baselineJars = configurations.baselineJars
def baseVersion = moduleIdentity.version.map { it.baseVersion.version }

dependencies {
    baseline("gradle:gradle:${compatibilityBaselineVersion}@zip")

    // This transform takes the Gradle zip distribution,
    // and unzips the Gradle jar files that it contains in a directory

                            junit testResults: '**/core-it-suite/target/surefire-reports/*.xml,**/core-it-support/**/target/surefire-reports/*.xml', allowEmptyResults: true
                            archiveDirs(stageId, ['core-it-suite-logs':'core-it-suite/target/test-classes',
                                                  'core-it-suite-reports':'core-it-suite/target/surefire-reports'])

var GlobalContext, cancelGlobalContext = context.WithCancel(context.Background())

// restartProcess starts a new process passing it the active fd's. It
// doesn't fork, but starts a new process using the same environment and
// arguments as when it was originally started. This allows for a newly
// deployed binary to be started. It returns the pid of the newly started
// process when successful.
func restartProcess() error {

    Sending a body with a `GET` request has an undefined behavior in the specifications, nevertheless, it is supported by FastAPI, only for very complex/extreme use cases.

    As it is discouraged, the interactive docs with Swagger UI won't show the documentation for the body when using `GET`, and proxies in the middle might not support it.

## Import Pydantic's `BaseModel`

First, you need to import `BaseModel` from `pydantic`:

By using all the previous alternatives I had the chance to learn from all of them, take ideas, and combine them in the best way I could find for myself and the teams of developers I have worked with.

For example, it was clear that ideally it should be based on standard Python type hints.

Also, the best approach was to use already existing standards.

  val firefox53 = sslLabsClients.first { it.userAgent == "Firefox" && it.version == "53" }
  val firefox73 = sslLabsClients.first { it.userAgent == "Firefox" && it.version == "73" }
  val java7 = sslLabsClients.first { it.userAgent == "Java" && it.version == "7u25" }
  val java12 = sslLabsClients.first { it.userAgent == "Java" && it.version == "12.0.1" }