7554e87374
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71 lines
2.3 KiB
Markdown
71 lines
2.3 KiB
Markdown
# Middleware
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Middleware are functions which are executed before or after requests to the
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server. They can be used to modify the *request to* or *response from*
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user-defined handler functions.
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There are two types of middleware: request and response. Both are declared
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using the `@app.middleware` decorator, with the decorator's parameter being a
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string representing its type: `'request'` or `'response'`. Response middleware
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receives both the request and the response as arguments.
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The simplest middleware doesn't modify the request or response at all:
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```python
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@app.middleware('request')
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async def print_on_request(request):
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print("I print when a request is received by the server")
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@app.middleware('response')
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async def print_on_response(request, response):
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print("I print when a response is returned by the server")
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```
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## Modifying the request or response
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Middleware can modify the request or response parameter it is given, *as long
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as it does not return it*. The following example shows a practical use-case for
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this.
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```python
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app = Sanic(__name__)
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@app.middleware('response')
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async def custom_banner(request, response):
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response.headers["Server"] = "Fake-Server"
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@app.middleware('response')
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async def prevent_xss(request, response):
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response.headers["x-xss-protection"] = "1; mode=block"
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app.run(host="0.0.0.0", port=8000)
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```
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The above code will apply the two middleware in order. First, the middleware
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**custom_banner** will change the HTTP response header *Server* to
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*Fake-Server*, and the second middleware **prevent_xss** will add the HTTP
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header for preventing Cross-Site-Scripting (XSS) attacks. These two functions
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are invoked *after* a user function returns a response.
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## Responding early
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If middleware returns a `HTTPResponse` object, the request will stop processing
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and the response will be returned. If this occurs to a request before the
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relevant user route handler is reached, the handler will never be called.
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Returning a response will also prevent any further middleware from running.
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```python
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@app.middleware('request')
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async def halt_request(request):
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return text('I halted the request')
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@app.middleware('response')
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async def halt_response(request, response):
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return text('I halted the response')
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```
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**Previous:** [Static Files](static_files.md)
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**Next:** [Exceptions](exceptions.md)
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