mirror of
https://github.com/metosin/reitit.git
synced 2025-12-17 08:21:11 +00:00
71 lines
3.5 KiB
Markdown
71 lines
3.5 KiB
Markdown
# Compiling Middleware
|
|
|
|
The [dynamic extensions](dynamic_extensions.md) 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.
|
|
|
|
Still, 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/interceptor at creation-time. It can do local reasoning: extract and transform relevant data just for it and pass it into the actual request-handler via a closure - yielding much faster runtime processing. It 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](data_driven_middleware.md) `:gen-wrap` key instead of the normal `:wrap`. `:gen-wrap` expects a function of `route-meta router-opts => ?wrap`.
|
|
|
|
To demonstrate the two approaches, below are response coercion middleware written as normal ring middleware function and as middleware record with `:gen-wrap`. Actual codes can be found in [`reitit.ring.coercion`](https://github.com/metosin/reitit/blob/master/src/reitit/ring/coercion.cljc):
|
|
|
|
## Naive
|
|
|
|
* Reads the compiled route information on every request.
|
|
|
|
```clj
|
|
(defn wrap-coerce-response
|
|
"Pluggable response coercion middleware.
|
|
Expects a :coercion of type `reitit.coercion.protocol/Coercion`
|
|
and :responses from route meta, otherwise will do nothing."
|
|
[handler]
|
|
(fn
|
|
([request]
|
|
(let [response (handler request)
|
|
method (:request-method request)
|
|
match (ring/get-match request)
|
|
responses (-> match :result method :meta :responses)
|
|
coercion (-> match :meta :coercion)
|
|
opts (-> match :meta :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 :meta :responses)
|
|
coercion (-> match :meta :coercion)
|
|
opts (-> match :meta :opts)]
|
|
(if (and coercion responses)
|
|
(let [coercers (response-coercers coercion responses opts)]
|
|
(handler request #(respond (coerce-response coercers request %))))
|
|
(handler request respond raise))))))
|
|
```
|
|
|
|
## Compiled
|
|
|
|
* Route information is provided via a closure
|
|
* Pre-compiled coercers
|
|
* Mounts only if `:coercion` and `:responses` are defined for the route
|
|
|
|
```clj
|
|
(require '[reitit.ring.middleware :as middleware])
|
|
|
|
(def gen-wrap-coerce-response
|
|
"Generator for pluggable response coercion middleware.
|
|
Expects a :coercion of type `reitit.coercion.protocol/Coercion`
|
|
and :responses from route meta, otherwise does not mount."
|
|
(middleware/create
|
|
{:name ::coerce-response
|
|
:gen-wrap (fn [{:keys [responses coercion opts]} _]
|
|
(if (and coercion responses)
|
|
(let [coercers (response-coercers coercion responses opts)]
|
|
(fn [handler]
|
|
(fn
|
|
([request]
|
|
(coerce-response coercers request (handler request)))
|
|
([request respond raise]
|
|
(handler request #(respond (coerce-response coercers request %)) raise)))))))}))
|
|
```
|
|
|
|
The latter has 50% less code, is easier to reason about and is much faster.
|