Signals `http.middleware.before` and `http.middleware.after` are dispatched for _every_ middleware

For a single request, the signals http.middleware.before and http.middleware.after are dispatched for every middle on the app.

Example app:

from sanic import Sanic
from sanic.response import html

app = Sanic(__name__)

@app.middleware("request")
def my_middleware1(request):
    print("Middleware 1 ran", flush=True)

@app.middleware("request")
def my_middleware2(request):
    print("Middleware 2 ran", flush=True)

@app.signal("http.middleware.before", condition={"attach_to": "request"})
def handle_mw_before(request, response=None):
    print("Before middleware", flush=True)

@app.signal("http.middleware.after", condition={"attach_to": "request"})
def handle_mw_after(request, response):
    print("After middleware", flush=True)

@app.get("/")
def index(request):
    return html("<p>hello world</p>")

if __name__ == "__main__":
    app.run(debug=True, auto_reload=False, access_log=False)

Output:

[2022-01-04 13:57:50 +1000] [47672] [INFO] Starting worker [47672]
[2022-01-04 13:57:54 +1000] [47672] [DEBUG] Dispatching signal: http.middleware.before
Before middleware
Middleware 1 ran
[2022-01-04 13:57:54 +1000] [47672] [DEBUG] Dispatching signal: http.middleware.after
After middleware
[2022-01-04 13:57:54 +1000] [47672] [DEBUG] Dispatching signal: http.middleware.before
Before middleware    #<--- Run again
Middleware 2 ran
[2022-01-04 13:57:54 +1000] [47672] [DEBUG] Dispatching signal: http.middleware.after
After middleware     #<--- Run again

Applicable section of code: https://github.com/sanic-org/sanic/blob/a7bc8b56bab01e066357e6dcc67c0dc9df864298/sanic/app.py#L1346-L1372

It appears this is done intentionally. I don’t know what the usefulness of running a handler for every middleware is, except for perhaps debug tracing or handler logger.

Maybe it makes sense to create two new signals like http.middleware.before_all and http.middleware.after_all, in a place like this:

await self.dispatch( 
    "http.middleware.before_all", 
    inline=True, 
    context={ 
        "request": request, 
        "response": None, 
    }, 
    condition={"attach_to": "request"}, 
)
response = None
if applicable_middleware and not request.request_middleware_started:
    request.request_middleware_started = True
    for middleware in applicable_middleware: 
         await self.dispatch( 
             "http.middleware.before", 
             inline=True, 
             context={ 
                 "request": request, 
                 "response": None, 
             }, 
             condition={"attach_to": "request"}, 
         ) 
      
         response = middleware(request) 
         if isawaitable(response): 
             response = await response 
      
         await self.dispatch( 
             "http.middleware.after", 
             inline=True, 
             context={ 
                 "request": request, 
                 "response": None, 
             }, 
             condition={"attach_to": "request"}, 
         ) 
      
         if response: 
             break
await self.dispatch( 
    "http.middleware.after_all", 
    inline=True, 
    context={ 
        "request": request, 
        "response": response, 
    }, 
    condition={"attach_to": "request"}, 
)
return response

[ahopkins]

We should probably also include a lifecycle diagram in the docs with the flow of handlers, middleware, and signals.

[stale[bot]]

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