6176964bdf
* Reorder and clarify the 'Request Data' guide, adding a section on RequestParameters * Clarify routing guide, adding introduction and HTTP types sections * Clarify the use-cases of middleware * Clean up formatting in the exceptions guide and add some common exceptions. * Fix formatting of blueprints and add use-case example. * Clarify the class-based views guide * Clarify and fix formatting of cookies guide * Clarify static files guide * Clarify the custom protocols guide. * Add more information to the deploying guide * Fix broken list in the community extensions list. * Add introduction and improve warning to contributing guide * Expand getting started guide * Reorder guides and add links between them * Standardise heading capitalisation
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Middleware
Middleware are functions which are executed before or after requests to the server. They can be used to modify the request to or response from user-defined handler functions.
There are two types of middleware: request and response. Both are declared
using the @app.middleware decorator, with the decorator's parameter being a
string representing its type: 'request' or 'response'. Response middleware
receives both the request and the response as arguments.
The simplest middleware doesn't modify the request or response at all:
@app.middleware('request')
async def print_on_request(request):
print("I print when a request is received by the server")
@app.middleware('response')
async def print_on_response(request, response):
print("I print when a response is returned by the server")
Modifying the request or response
Middleware can modify the request or response parameter it is given, as long as it does not return it. The following example shows a practical use-case for this.
app = Sanic(__name__)
@app.middleware('response')
async def custom_banner(request, response):
response.headers["Server"] = "Fake-Server"
@app.middleware('response')
async def prevent_xss(request, response):
response.headers["x-xss-protection"] = "1; mode=block"
app.run(host="0.0.0.0", port=8000)
The above code will apply the two middleware in order. First, the middleware custom_banner will change the HTTP response header Server to Fake-Server, and the second middleware prevent_xss will add the HTTP header for preventing Cross-Site-Scripting (XSS) attacks. These two functions are invoked after a user function returns a response.
Responding early
If middleware returns a HTTPResponse object, the request will stop processing
and the response will be returned. If this occurs to a request before the
relevant user route handler is reached, the handler will never be called.
Returning a response will also prevent any further middleware from running.
@app.middleware('request')
async def halt_request(request):
return text('I halted the request')
@app.middleware('response')
async def halt_response(request, response):
return text('I halted the response')
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