Handlers

Gate handlers are functions that accept a request and return something.

(defn a-handler
  [request]

  (let [name (get-in request [:params :name])]
    (str "Hello, " name ". I am a handler.")))

---

handler and defhandler

Manually retrieving params from the request like in the example above means writing the same boilerplate over and over, and that's no fun. Luckily, there's a macro for that: gate/defhandler. The following example creates exactly the same handler as in the previous example.

(defhandler a-handler
  [name]

  (str "Hello, " name ". I am a handler."))

Another problem commonly encountered when writing handlers to is that all params are strings, even when a param represents data that isn't a string, so you often need to transform a param into the appropriate type of data before your app can use it.

In the following example, the function get-user requires a user-id as a number. Usually you would have to call Integer/parseInt or some similar function on your user-id param before you could pass it to get-user, but defhandler can make that conversion for you.

(defhandler get-user-profile
  [user-id :- Number]

  (let [user (get-user user-id)]
    (render-profile user))

Parameters can currently be coerced from strings into Keyword, Boolean, Number, Long, Integer, Double, java.util.UUID, or Edn. If a parameter can not be coerced, it remains in its original form.

Keyword, Boolean, Number, and Edn all have behaviors that warrant an explanation.

---

Keyword

Strings are made lower-case before being converted into keywords.

---

Boolean

Behaves like Boolean/parseBoolean, which accepts any capitalization of "true" as true and returns false for any other string.

---

Number

If the number you are trying to parse contains a decimal point, attempts to parse it as a Double. If the number you are trying to parse contains no decimal point, attempts to parse it as a Long. If the number can't be parsed as a long, attempts to read it via edn/read-string.

Will return either Double, Long, BigInt, or Ratio.

---

Edn

Uses edn/read-string to parse parameter.