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84 lines
2.9 KiB
Markdown
84 lines
2.9 KiB
Markdown
# Transforming the Interceptor Chain
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There is an extra option in http-router (actually, in the underlying interceptor-router): `:reitit.interceptor/transform` to transform the interceptor chain per endpoint. Value should be a function or a vector of functions that get a vector of compiled interceptors and should return a new vector of interceptors.
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**Note:** the last interceptor in the chain is usually the handler, compiled into an Interceptor. Applying a transformation `clojure.core/reverse` would put this interceptor into first in the chain, making the rest of the interceptors effectively unreachable. There is a helper `reitit.interceptor/transform-butlast` to transform all but the last interceptor.
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## Example Application
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```clj
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(require '[reitit.http :as http])
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(require '[reitit.interceptor.sieppari :as sieppari])
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(defn interceptor [message]
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{:enter (fn [ctx] (update-in ctx [:request :message] (fnil conj []) message))})
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(defn handler [req]
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{:status 200
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:body (select-keys req [:message])})
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(def app
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(http/ring-handler
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(http/router
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["/api" {:interceptors [(interceptor 1) (interceptor 2)]}
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["/ping" {:get {:interceptors [(interceptor 3)]
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:handler handler}}]])
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{:executor sieppari/executor}))
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(app {:request-method :get, :uri "/api/ping"})
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; {:status 200, :body {:message [1 2 3]}}
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```
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### Reversing the Interceptor Chain
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```clj
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(def app
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(http/ring-handler
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(http/router
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["/api" {:interceptors [(interceptor 1) (interceptor 2)]}
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["/ping" {:get {:interceptors [(interceptor 3)]
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:handler handler}}]]
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{::interceptor/transform (interceptor/transform-butlast reverse)})
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{:executor sieppari/executor}))
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(app {:request-method :get, :uri "/api/ping"})
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; {:status 200, :body {:message [3 2 1]}}
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```
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### Interleaving Interceptors
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```clj
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(def app
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(http/ring-handler
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(http/router
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["/api" {:interceptors [(interceptor 1) (interceptor 2)]}
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["/ping" {:get {:interceptors [(interceptor 3)]
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:handler handler}}]]
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{::interceptor/transform #(interleave % (repeat (interceptor :debug)))})
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{:executor sieppari/executor}))
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(app {:request-method :get, :uri "/api/ping"})
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; {:status 200, :body {:message [1 :debug 2 :debug 3 :debug]}}
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```
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### Printing Context Diffs
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```clj
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[metosin/reitit-interceptors "0.9.2"]
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```
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Using `reitit.http.interceptors.dev/print-context-diffs` transformation, the context diffs between each interceptor are printed out to the console. To use it, add the following router option:
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```clj
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:reitit.interceptor/transform reitit.http.interceptor.dev/print-context-diffs
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```
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Sample output:
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Sample applications (uncomment the option to see the diffs):
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* Sieppari: https://github.com/metosin/reitit/blob/master/examples/http-swagger/src/example/server.clj
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* Pedestal: https://github.com/metosin/reitit/blob/master/examples/pedestal-swagger/src/example/server.clj
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