Python Falcon 简明教程

Python Falcon - Hooks

钩子是在响应客户端请求时在资源类中的特定响应程序方法被调用时自动执行的用户定义函数。Falcon 支持 before 和 after 钩子。

Hooks are the user defined functions that are executed automatically when a specific responder method in the resource class is invoked in response to the client request. Falcon supports before and after hooks.

作为钩子使用的函数被定义为具有请求、响应和资源类的参数，除了可能需要的任何可选参数。

A function to be used as a hook is defined with the request, response and resource class as parameters, in additional to any optional parameters as may be necessary.

def hookfunction(req, resp, resource):
   . . . . .
   . . . . .

此类函数通过应用以下装饰器之一附加到单个响应程序或整个资源类 -

Such a function is attached to either an individual responder or the entire resource class by applying one of the following decorators −

@falcon.before(hookfunction)
@falcon.after(hookfunction)

将 before 钩子应用于 on_post() 响应程序 -

To apply the before hook to the on_post() responder −

@falcon.before(hookfunction)
def on_post(self, req, resp):
   . . .
   . . .

应用一个 after 钩子 -

To apply an after hook −

@falcon.after(hookfunction)
def on_get(self, req, resp):
   . . .
   . . .

要装饰整个资源类，请在类声明上方使用装饰器 -

To decorate the entire resource class, use the decorator above the declaration of the class −

@falcon.after(hookfunction)
class SomeResource:
 def on_get(self, req, resp):
   . . .
   . . .
   def on_post(self, req, resp):
   . . .
   . . .

在以下示例中，我们有 StudentResource 类，其中已定义 on_get() 和 on_post() 响应程序。当 POST 请求发送一些数据并且使用它创建的新 dict 对象被添加到 Students 列表中时，会调用 on_post() 响应程序。

In the following example, we have the StudentResource class in which on_get() and on_post() responders have been defined. The on_post() responder is invoked when a POST request sends some data and a new dict object created with it is added in the Students list.

接收到的数据需要在处理之前进行验证。为此，已定义以下函数。它检查 percent 参数的值是否在 0 和 100 之间。仅当数据通过此条件时，才将其传递给响应程序。

The data received needs to be validated before processing. For this purpose, the following function has been defined. It checks whether value of percent parameter is between 0 and 100. Only if the data passes this condition, it is passed to the responder.

def checkinput(req, resp, resource,params):
   student = json.load(req.bounded_stream)
   if "name" not in student:
      raise falcon.HTTPBadRequest(
         title="Bad request", description="Bad input, name must be provided."
      )

   per=int(student['percent'])
   if per<0 or per>100:
      raise falcon.HTTPBadRequest(
         title="Bad request", description="Bad input, invalid percentage"
      )
      req.context.data = student

此函数作为 StudentResource 类的 on_post() 响应程序上的钩子应用。

This function is applied as a hook on the on_post() responder of the StudentResource class.

import falcon
import json
from waitress import serve
students = [
   {"id": 1, "name": "Ravi", "percent": 75.50},
   {"id": 2, "name": "Mona", "percent": 80.00},
   {"id": 3, "name": "Mathews", "percent": 65.25},
]
class StudentResource:
   def on_get(self, req, resp):
      resp.text = json.dumps(students)
      resp.status = falcon.HTTP_OK
      resp.content_type = falcon.MEDIA_JSON
   @falcon.before(checkinput)
   def on_post(self, req, resp):
      student = json.load(req.context.data)
      students.append(student)
      resp.text = "Student added successfully."
      resp.status = falcon.HTTP_OK
      resp.content_type = falcon.MEDIA_TEXT

   def on_get_student(self, req, resp, id):
      resp.text = json.dumps(students[id-1])
      resp.status = falcon.HTTP_OK
      resp.content_type = falcon.MEDIA_JSON
app = falcon.App()
app.add_route("/students", StudentResource())
if __name__ == '__main__':
   serve(app, host='0.0.0.0', port=8000)

让我们运行 Waitress 服务器并发起 POST 请求。

Let us run the Waitress server and initiate the POST request.

http POST localhost:8000/students id=4 percent=50
HTTP/1.1 400 Bad Request
Content-Length: 76
Content-Type: application/json
Date: Tue, 26 Apr 2022 14:49:07 GMT
Server: waitress
Vary: Accept {
   "description": "Bad input, name must be provided.",
   "title": "Bad request"
}

由于数据不包含 name 参数的值，因此引发异常。

Since the data doesn’t contain value of name parameter, the exception is raised.

在下面显示的另一个 POST 请求中，percent 参数的值未满足所需条件，因此会引发异常。

In another POST request as shown below, the value of percent parameter fails to meet the required criteria, hence the exception.

http POST localhost:8000/students id=4 name="aaa" percent=500
HTTP/1.1 400 Bad Request
Content-Length: 72
Content-Type: application/json
Date: Tue, 26 Apr 2022 15:01:20 GMT
Server: waitress
Vary: Accept {
   "description": "Bad input, invalid percentage",
   "title": "Bad request"
}