## 使用回调的应用

示例如下。

假设要开发一个创建发票的应用。

发票包括 `id`、`title`（可选）、`customer`、`total` 等属性。

API 的用户 （外部开发者）要在您的 API 内使用 POST 请求创建一条发票记录。

（假设）您的 API 将：

* 把发票发送至外部开发者的消费者
* 归集现金
* 把通知发送至 API 的用户（外部开发者）
    * 通过（从您的 API）发送 POST 请求至外部 API （即**回调**）来完成

## 常规 **FastAPI** 应用

添加回调前，首先看下常规 API 应用是什么样子。

常规 API 应用包含接收 `Invoice` 请求体的*路径操作*，还有包含回调 URL 的查询参数 `callback_url`。

furnished to do so, subject to...

/**
 * @author shinsuke
 *
 */
public final class Constants {
    public static final String GET_METHOD = "GET";

    public static final String HEAD_METHOD = "HEAD";

    public static final String POST_METHOD = "POST";

    public static final int OK_STATUS = 0;

    public static final int NOT_MODIFIED_STATUS = 304;

    public static final int OK_STATUS_CODE = 200;

    public static final int NOT_MODIFIED_STATUS_CODE = 304;

class Item:
    name: str
    description: Union[str, None] = None


@dataclass
class Author:
    name: str
    items: List[Item] = field(default_factory=list)  # (3)


app = FastAPI()


@app.post("/authors/{author_id}/items/", response_model=Author)  # (4)
async def create_author_items(author_id: str, items: List[Item]):  # (5)
    return {"name": author_id, "items": items}  # (6)

    @Required
    @Size(max = 1000)
    public String segmentation;

    @Required
    @Size(max = 1000)
    public String reading;

    @Required
    @Size(max = 1000)
    public String pos;

    public void initialize() {
        crudMode = CrudMode.CREATE;
    }

        return offset + 4;
    }


    static int writeSecurityBufferContent ( byte[] dest, int pos, int off, byte[] src ) {
        writeULong(dest, off, pos);
        if ( src != null && src.length > 0 ) {
            System.arraycopy(src, 0, dest, pos, src.length);
            return src.length;
        }
        return 0;
    }


    static String getOEMEncoding () {

            // server is set through URL, however it's still in the name
            int pos = 0;
            if ( context.getServer() == null ) {
                pos = 1;
            }

            // first remaining path element would be share
            if ( nameParts.length > pos ) {
                this.share = nameParts[ pos++ ];
            }

            // all other remaining path elements are actual path

    current_user: Annotated[User, Depends(get_current_user)],
):
    if current_user.disabled:
        raise HTTPException(status_code=400, detail="Inactive user")
    return current_user


@app.post("/token")
async def login(form_data: Annotated[OAuth2PasswordRequestForm, Depends()]):
    user_dict = fake_users_db.get(form_data.username)
    if not user_dict:

    current_user: Annotated[User, Depends(get_current_user)],
):
    if current_user.disabled:
        raise HTTPException(status_code=400, detail="Inactive user")
    return current_user


@app.post("/token")
async def login(form_data: Annotated[OAuth2PasswordRequestForm, Depends()]):
    user_dict = fake_users_db.get(form_data.username)
    if not user_dict:

    # Update the viewport manually
    context = browser.new_context(viewport={"width": 960, "height": 1080})
    page = context.new_page()
    page.goto("http://localhost:8000/docs")
    page.get_by_role("button", name="POST /login/ Login").click()
    page.get_by_role("button", name="Try it out").click()
    # Manually add the screenshot
    page.screenshot(path="docs/en/docs/img/tutorial/request-form-models/image01.png")