The dynamic extensions is a easy way to extend the system. To enable fast lookups into route data, we can compile them into any shape (records, functions etc.) we want, enabling fast access at request-time.
But, we can do much better. As we know the exact route that middleware/interceptor is linked to, we can pass the (compiled) route information into the middleware at creation-time. It can do local reasoning: extract and transform relevant data just for it and pass the optimized data into the actual request-handler via a closure - yielding much faster runtime processing. Middleware can also decide not to mount itself by returning nil
. Why mount a wrap-enforce-roles
middleware for a route if there are no roles required for it?
To enable this we use middleware records :compile
key instead of the normal :wrap
. :compile
expects a function of route-data router-opts => ?IntoMiddleware
.
To demonstrate the two approaches, below are response coercion middleware written as normal ring middleware function and as middleware record with :compile
.
(defn wrap-coerce-response
"Middleware for pluggable response coercion.
Expects a :coercion of type `reitit.coercion/Coercion`
and :responses from route data, otherwise will do nothing."
[handler]
(fn
([request]
(let [response (handler request)
method (:request-method request)
match (ring/get-match request)
responses (-> match :result method :data :responses)
coercion (-> match :data :coercion)
opts (-> match :data :opts)]
(if (and coercion responses)
(let [coercers (response-coercers coercion responses opts)]
(coerce-response coercers request response))
response)))
([request respond raise]
(let [method (:request-method request)
match (ring/get-match request)
responses (-> match :result method :data :responses)
coercion (-> match :data :coercion)
opts (-> match :data :opts)]
(if (and coercion responses)
(let [coercers (response-coercers coercion responses opts)]
(handler request #(respond (coerce-response coercers request %))))
(handler request respond raise))))))
:coercion
and :responses
are defined for the route:responses
for the route data validation.(require '[reitit.spec :as rs])
(def coerce-response-middleware
"Middleware for pluggable response coercion.
Expects a :coercion of type `reitit.coercion/Coercion`
and :responses from route data, otherwise does not mount."
{:name ::coerce-response
:spec ::rs/responses
:compile (fn [{:keys [coercion responses]} opts]
(if (and coercion responses)
(let [coercers (coercion/response-coercers coercion responses opts)]
(fn [handler]
(fn
([request]
(coercion/coerce-response coercers request (handler request)))
([request respond raise]
(handler request #(respond (coercion/coerce-response coercers request %)) raise)))))))})
It has 50% less code, it's much easier to reason about and is much faster.
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