---

If you are using a third party library that communicates with something (a database, an API, the file system, etc.) and doesn't have support for using `await`, (this is currently the case for most database libraries), then declare your *path operation functions* as normally, with just `def`, like:

```Python hl_lines="2"
@app.get('/')
def results():
    results = some_library()
    return results
```

        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,
    proxyType: Proxy.Type,
  ): Boolean {

 *
 * By orchestrating two different servers with the same port but different IP addresses, we can
 * test what OkHttp does when both are reachable, or if only one is reachable.
 *
 * This test only runs on host machines that have both IPv4 and IPv6 addresses for localhost.
 */
@Timeout(30)
class FastFallbackTest {
  @RegisterExtension
  val clientTestRule = OkHttpClientTestRule()

* If you can't understand the question, ask for more **details**.

### Reproduce the problem

For most of the cases and most of the questions there's something related to the person's **original code**.

In many cases they will only copy a fragment of the code, but that's not enough to **reproduce the problem**.

* Automatic data model documentation with <a href="https://json-schema.org/" class="external-link" target="_blank"><strong>JSON Schema</strong></a> (as OpenAPI itself...

    val request =
      Request.Builder()
        .url("http://square.com/")
        .header("Connection", "upgrade")
        .header("Upgrade", "websocket")
        .header("Host", "square.com")
        .header("TE", "gzip")
        .build()
    val expected =
      headerEntries(
        ":method",
        "GET",
        ":path",
        "/",
        ":authority",

!!! tip
    The next sections are **not necessarily "advanced"**.

    And it's possible that for your use case, the solution is in one of them.

## Read the Tutorial first

You could still use most of the features in **FastAPI** with the knowledge from the main [Tutorial - User Guide](../tutorial/index.md){.internal-link target=_blank}.

And the next sections assume you already read it, and assume that you know those main ideas.

    val client =
      clientTestRule.newClientBuilder()
        .proxy(socksProxy.proxy())
        .build()
    val url =
      server.url("/")
        .newBuilder()
        .host(SocksProxy.HOSTNAME_THAT_ONLY_THE_PROXY_KNOWS)
        .build()
    val request = Request.Builder().url(url).build()
    val response1 = client.newCall(request).execute()

    **FastAPI** provides the same `starlette.responses` as `fastapi.responses` just as a convenience for you, the developer. But most of the available responses come directly from Starlette.

    And as the `Response` can be used frequently to set headers and cookies, **FastAPI** also provides it at `fastapi.Response`.

## Custom Headers

    calls++

    if (exchange != null) {
      check(exchange.finder.routePlanner.sameHostAndPort(request.url)) {
        "network interceptor ${interceptors[index - 1]} must retain the same host and port"
      }
      check(calls == 1) {
        "network interceptor ${interceptors[index - 1]} must call proceed() exactly once"
      }
    }

    // Call the next interceptor in the chain.