* proxy server can issue an auth challenge and then close the connection.
   *
   * @return the next plan to attempt, or null if no further attempt should be made either because
   *     we've successfully connected or because no further attempts should be made.
   */
  @Throws(IOException::class)
  internal fun connectTunnel(): ConnectResult {
    val nextTunnelRequest =
      createTunnel()

  </plugin>
  .
  .
  .
</plugins>

<img src="/img/tutorial/dataclasses/image01.png">

## Dataclasses in Nested Data Structures { #dataclasses-in-nested-data-structures }

You can also combine `dataclasses` with other type annotations to make nested data structures.

In some cases, you might still have to use Pydantic's version of `dataclasses`. For example, if you have errors with the automatically generated API documentation.

As **FastAPI** is based on Starlette and implements the <abbr title="Asynchronous Server Gateway Interface">ASGI</abbr> specification, you can use any ASGI middleware.

A middleware doesn't have to be made for FastAPI or Starlette to work, as long as it follows the ASGI spec.

In general, ASGI middlewares are classes that expect to receive an ASGI app as the first argument.

 *
 * <p>Tests should inherit from this class, and declare subtyping relationship with public methods
 * annotated by {@link TestSubtype}.
 *
 * <p>These declaration methods rely on Java static type checking to make sure what we want to
 * assert as subtypes are really subtypes according to javac. For example:
 *
 * {@snippet :
 * class MySubtypeTests extends SubtypeTester {

     conditions on any use of the Licensed Material that could lawfully
     be made without permission under this Public License.

  b. To the extent possible, if any provision of this Public License is
     deemed unenforceable, it shall be automatically reformed to the
     minimum extent necessary to make it enforceable. If the provision
     cannot be reformed, it shall be severed from this Public License

	// HealthCheckTimeout determines timeout for each call.
	HealthCheckTimeout time.Duration

	// MaxErrResponseSize is the maximum expected response size.
	// Should only be modified before any calls are made.
	MaxErrResponseSize int64

	// Avoid metrics update if set to true
	NoMetrics bool

	// TraceOutput will print debug information on non-200 calls if set.
	TraceOutput io.Writer // Debug trace output

For example, if some code at some point in the middle, in another dependency or in a *path operation*, made a database transaction "rollback" or created any other exception, you would receive the exception in your dependency.

So, you can look for that specific exception inside the dependency with `except SomeException`.

In the same way, you can use `finally` to make sure the exit steps are executed, no matter if there was an exception or not.

This includes many libraries to interact with cloud storage, video processing, and others.

{* ../../docs_src/custom_response/tutorial008_py39.py hl[2,10:12,14] *}

1. This is the generator function. It's a "generator function" because it contains `yield` statements inside.

and informs licensees how to obtain it in a reasonable manner on or through
a medium customarily used for software exchange.

   When the Program is made available in source code form:

      a) it must be made available under this Agreement; and

b) a copy of this Agreement must be included with each copy of the Program.

Contributors may not remove or alter any copyright notices contained within