Argument Resolvers

In Rook, endpoint functions may have many parameters, in contrast to a traditional Ring handler (or middleware), or a Pedestal interceptor.

Argument resolvers are the bridge between the Pedestal context and the individual parameters of an endpoint function.

The :arg-resolvers option is a map from keyword to argument resolver generator.

When a parameter of an endpoint function has metadata with the matching key, the generator is invoked.

The generator is passed the parameter symbol, and returns the arg resolver function; this function is passed the Pedestal context and returns the argument value.

By convention, when the metadata value is true, the symbol is converted to a keyword.

So, if an endpoint function has a parameter ^:request body, the :request argument resolver will return a function equivalent to:

(fn [context]
  (let [v (get-in context [:request :body])]
    (if (some? v)
      v
      (throw (ex-info ...)))))