Probably the main use case for this is if you already have some autogenerated client code/SDKs and you don't want to update all the autogenerated client code/SDKs yet, you probably will want to do it at some point, but maybe not right now.

In that case, you can disable this feature in **FastAPI**, with the parameter `separate_input_output_schemas=False`.

/// info

Support for `separate_input_output_schemas` was added in FastAPI `0.102.0`. 🤓

Your API almost always has to send a **response** body. But clients don't necessarily need to send **request bodies** all the time, sometimes they only request a path, maybe with some query parameters, but don't send a body.

To declare a **request** body, you use <a href="https://docs.pydantic.dev/" class="external-link" target="_blank">Pydantic</a> models with all their power and benefits.

/// info

/// tip

The `shutdown` would happen when you are **stopping** the application.

Maybe you need to start a new version, or you just got tired of running it. 🤷

///

### Lifespan function { #lifespan-function }

If the client tries to go to `/items`, by default, it would be redirected to `/items/`.

But before setting the *CLI Option* `--forwarded-allow-ips` it could redirect to `http://localhost:8000/items/`.

But maybe your application is hosted at `https://mysuperapp.com`, and the redirection should be to `https://mysuperapp.com/items/`.

By setting `--proxy-headers` now FastAPI would be able to redirect to the right location. 😎

```

Then we can test that it is used.

## Reading a `.env` file { #reading-a-env-file }

If you have many settings that possibly change a lot, maybe in different environments, it might be useful to put them on a file and then read them from it as if they were environment variables.

    as a dependency. All other OAuth2 classes inherit from it and customize it for
    each OAuth2 flow.

    You normally would not create a new class inheriting from it but use one of the
    existing subclasses, and maybe compose them if you want to support multiple flows.

    Read more about it in the
    [FastAPI docs for Security](https://fastapi.tiangolo.com/tutorial/security/).
    """

    def __init__(
        self,

			}
		default:
			// This is where we'd set it to -1 (at least
			// if body != NoBody) to mean unknown, but
			// that broke people during the Go 1.8 testing
			// period. People depend on it being 0 I
			// guess. Maybe retry later. See Issue 18117.
		}
		// For client requests, Request.ContentLength of 0
		// means either actually 0, or unknown. The only way
		// to explicitly say that the ContentLength is zero is

		defer func() {
			fmt.Println("Mux", m.MuxID, "Request took", time.Since(start).Round(time.Millisecond))
		}()
	}
	defer func() {
		// addErrorNonBlockingClose will close the response channel
		// - maybe async, so we shouldn't do it here.
		if m.respErr.Load() == nil {
			xioutil.SafeClose(respHandler)
		}
	}()
	var pingTimer <-chan time.Time
	if m.deadline == 0 || m.deadline > m.clientPingInterval {

			format.mustNotBe(FormatUSTAR)
		}
	*/

	// Check desired format.
	if wantFormat := h.Format; wantFormat != FormatUnknown {
		if wantFormat.has(FormatPAX) && !preferPAX {
			wantFormat.mayBe(FormatUSTAR) // PAX implies USTAR allowed too
		}
		format.mayOnlyBe(wantFormat) // Set union of formats allowed and format wanted
	}
	if format == FormatUnknown {
		switch h.Format {
		case FormatUSTAR:

                slf4jLogger.debug(buff.toString());
            }
        }
    }

    // Needed to make this method package visible to make writing a unit test possible
    // Maybe it's better to move some of those methods to separate class (SoC).
    void properties(CliRequest cliRequest) throws Exception {
        Properties paths = new Properties();
        if (cliRequest.topDirectory != null) {