# Background Tasks

You can define background tasks to be run *after* returning a response.

This is useful for operations that need to happen after a request, but that the client doesn't really have to be waiting for the operation to complete before receiving the response.

This includes, for example:

* Email notifications sent after performing an action:

    enforce strict null checks.

 *  New: The response message is now non-null. This is the "Not Found" in the
    status line "HTTP 404 Not Found". If you are building responses
    programmatically (with `new Response.Builder()`) you must now always supply
    a message. An empty string `""` is permitted. This value was never null on
    responses returned by OkHttp itself, and it was an old mistake to permit

@app.get("/items/")
async def read_items(commons: Annotated[Any, Depends(CommonQueryParams)]):
    response = {}
    if commons.q:
        response.update({"q": commons.q})
    items = fake_items_db[commons.skip : commons.skip + commons.limit]
    response.update({"items": items})

client = TestClient(app)


def test():
    log = Path("log.txt")
    if log.is_file():
        os.remove(log)  # pragma: no cover
    response = client.post("/send-notification/******@****.***?q=some-query")
    assert response.status_code == 200, response.text
    assert response.json() == {"message": "Message sent"}
    with open("./log.txt") as f:

    if err == nil {
        fmt.Println("Got response with field", resp["result"])
    }
```

The wrapper will handle all serialization and de-seralization of the request and response,
and furthermore provides reuse of the structs used for the request and response.

Note that Responses sent for serialization are automatically reused for similar requests.

            .withQueryStringParameter("name", "peter"),
        )
        .respond(response().withBody("Peter the person!"))

      val results =
        (1..20).map {
          executor.submit {
            val response =
              client.newCall(Request((mockServer.secureEndpoint + "/person?name=peter").toHttpUrl())).execute()

            val body = response.body.string()
            assertThat(body).contains("Peter the person")

    client = TestClient(app)
    log = Path("log.txt")
    if log.is_file():
        os.remove(log)  # pragma: no cover
    response = client.post("/send-notification/******@****.***?q=some-query")
    assert response.status_code == 200, response.text
    assert response.json() == {"message": "Message sent"}
    with open("./log.txt") as f:

    client = TestClient(app)
    log = Path("log.txt")
    if log.is_file():
        os.remove(log)  # pragma: no cover
    response = client.post("/send-notification/******@****.***?q=some-query")
    assert response.status_code == 200, response.text
    assert response.json() == {"message": "Message sent"}
    with open("./log.txt") as f:

        .url("https://publicobject.com/helloworld.txt")
        .build();

    try (Response response = client.newCall(request).execute()) {
      System.out.println(response.request().header("Date"));
    }
  }

  static class CurrentDateInterceptor implements Interceptor {
    @Override public Response intercept(Chain chain) throws IOException {
      Request request = chain.request();

    /**
     * {@inheritDoc}
     *
     * @see jcifs.util.transport.Response#error()
     */
    @Override
    public final void error () {
        this.error = true;
        synchronized ( this ) {
            notifyAll();
        }
    }


    /**
     * {@inheritDoc}
     *
     * @see jcifs.util.transport.Response#clearReceived()
     */
    @Override