Add mechanism to enable Jackson Features

[poernahi]

Currently, the API does not expose a way to enable jackson's encoder/decoder features. It looks like the only way to do this is through the :mapper key in [:formats "application/json" :decoder-opts] or [:formats "application/json" :encoder-opts].

Use case example:
For compatibility, I would like to enable com.fasterxml.jackson.core.JsonParser.Feature/ALLOW_UNQUOTED_CONTROL_CHARS

I think some change in jsonista is required to support this.

I propose adding an option key, maybe named features, where library consumer can pass a map of features. jsonista can then call .configure on each item. Or the features could be translated to clojure keywords.

Example:

(ns project.middleware.formats
  (:require [muuntaja.core :as m])
  (:import (com.fasterxml.jackson.core JsonParser$Feature)))

(def instance
  (m/create
    (-> m/default-options
        (update-in [:formats "application/json" :decoder-opts]
          (partial merge {:features {JsonParser$Feature/ALLOW_UNQUOTED_CONTROL_CHARS true}})))))

;; in jsonista
(defn ^ObjectMapper object-mapper
  "..."
  ([options]
    (doto (ObjectMapper.)
      ;; ...
      (#(doseq [[k v] (:features options)] (.configure % k v))))))

I can create PR if the proposal is blessed. Thanks!

[ikitommi]

There seem to be at least the following type of features, that all can be configured in the ObjectMapper:

• DeserializationFeature
• JsonGenerator.Feature
• JsonParser.Feature
• MapperFeature
• SerializationFeature

I think it would be good to be able to set any of these easily.

option 1: document how to do this the Java-way

• add the features to the ObjectMapper returned via the j/object-mapper, e.g.

(def mapper
  (doto (j/object-mapper)
    (.enable JsonParser$Feature/ALLOW_UNQUOTED_CONTROL_CHARS)))

• mount the mapper to Muuntaja via :mapper option:

(def muuntaja
  (m/create
    (assoc-in
      m/default-options
      [:formats "application/json" :opts]
      {:mapper mapper})))

• enjoy

option 2: make it easier

• add a new configuration key for all features, :features, which takes a sequence of features

(j/object-mapper {:features [JsonParser$Feature/ALLOW_UNQUOTED_CONTROL_CHARS ...]})

(def muuntaja
  (m/create
    (assoc-in
      m/default-options
      [:formats "application/json" :opts]
      {:features [JsonParser$Feature/ALLOW_UNQUOTED_CONTROL_CHARS ...]})))

option 3: all-clojure

• map all the options as clojure keywords for even easier config
• naming the features, maybe: :json-parser/allow-unquoted-control-chars?
• the mapping between clojure & java should be automatic: new features -> just work. I would guess this would need helper functions like (j/parser-features), (j/serialization-features), ... which would list all the possible values via Class scanning. Best would be if one could also get the descriptions so it would return a map of key -> description. I guess that would need a javadoc scraper...

(j/object-mapper {:features #{:json-parser/allow-unquoted-control-chars ...}})

(def muuntaja
  (m/create
    (assoc-in
      m/default-options
      [:formats "application/json" :opts]
      {:features #{:json-parser/allow-unquoted-control-chars ...}})))

thoughts?

[poernahi]

I thought about option 1 but it will silently ignore other keys in :opts, possibly causing bugs?
For example, I think the sample code above will ignore the default {:decode-key-fn true}.

https://github.com/metosin/muuntaja/blob/master/modules/muuntaja/src/muuntaja/format/json.clj#L13