Clojure

A Clojure library designed to easily encode and decode protobuf messages by using Clojure maps.

Installation

Add the below dependency to your project.clj file:

           [io.odpf/stencil-clj "0.2.1"]

Usage

Consider following proto message

syntax = "proto3";

package example;

option java_multiple_files = true;
option java_package = "io.odpf.CljTest";

message Address {
	string city = 1;
	string street = 2;
}

message Person {
	enum Gender {
		UNKNOWN = 0;
		MALE = 1;
		FEMALE = 2;
		NON_BINARY = 3;
	}
	string name = 1;
	Address address = 2;
	Gender gender = 3;
	repeated string email_list = 4;
	int32 age = 5;
}

1. Create stencil client. You can refer to java client documentation for all available options.

(ns test
  (:require [stencil.core :refer [create-client]]))

(def client (create-client {:url "<stencil service url>"
                :refresh-cache true
                :refresh-strategy :version-based-refresh
                :headers {"<headerkey>" "<header value>"}))

2. To serialize data from clojure map

(:require [stencil.core :refer [serialize]])

(def serialized-data
     (serialize client "io.odpf.CljTest" {:name "Foo"
                                          :address {:street "bar"}
                                          :email-list ["a@example.com" "b@b.com"]
                                          :gender :NON-BINARY
                                          :age 10}))

3. Deserialize data from bytes to clojure map

(:require [stencil.core :refer [deserialize]])

(deserialize client "io.odpf.CljTest" serialized-data)
;; prints
;; {:name "Foo"
;; :address {:street "bar"}
;; :email-list ["a@example.com" "b@b.com"]
;; :gender :NON-BINARY
;; :age 10}

Protocol buffers - Clojure interop

Protobuf	Clojure	Notes
field names	keywords in kebab case	name -> :name, field_name -> :field-name
scalar fields	Values follow protobuf-java scalar value mappings
enums	Values converted as keywords of enum's original value	UNKNOWN -> :UNKNOWN
messages	clojure map	message Hello {string name = 1;} -> {:name "odpf"}
repeated fields	clojure vector
one-of fields	treated as regular fields	if two fields are set that are part of one-of, last seen value is considered while serializing data
map	map values follow it's wire representation	for map<string, string> type, example value will be [{:key "key" :value "value"}]

Note on errors: Serialize will throw error in following cases

1. unknown field is passed that's not present in schema {:cause :unknown-field :info {:field-name <field-name>}}
2. if non-collection type is passed to repeated field {:cause :not-a-collection :info {:value <value>}}
3. If unknown enum value passed that's not present in schema {:cause :unknown-enum-value :info {:field-name <field-name>}}

API

• create-client (client-config)

  Returns a new Stencil Clojure client instance by passing client-config.

  Client config structure :

  Key	Type	Description
  url	String	Stencil url to fetch latest descriptor sets
  refresh-cache	Boolean	Whether the cache should be refreshed or not
  refresh-ttl	Integer	Cache TTL in minutes
  request-timeout	Integer	Request timeout in milliseconds
  request-backoff-time	Integer	Request back off time in minutes
  retry-count	Integer	Number of retries to be made to fetch descriptor sets
  headers	Map	Map with key as header key and value as header value, which will be passed to stencil server
  refresh-strategy	keyword	Possible values :version-based-refresh, :long-polling-refresh. Default :long-polling-refresh

  Example:

   (let [sample-client-config {:url       "https://example-url"
                              :refresh-cache        true
                              :refresh-ttl          100
                              :request-timeout      10000
                              :request-backoff-time 100
                              :retry-count          3
                              :headers              {"Authorization" "Bearer <token>"}
                              :refresh-strategy     :version-based-refresh
                              }]
         (create-client sample-client-config))
  

• get-descriptor (client proto-class-name)

  Returns protobuf descriptor object for the given protobuf class name.

  Argument list :

  Key	Type	Description
  client	Object	Instantiated Clojure client object
  proto-class-name	String	Name of the proto class whose proto descriptor object is required

  Response structure

  Value	Type	Description
  proto-desc	Object	Protobuf descriptor for given proto class name

  Example:

  (let [client (create-client sample-client-config)
        proto-package "io.odpf.stencil_clj_test"
        proto-class-name "Scalar"
        fully-qualified-proto-name (str proto-package "." proto-class-name)]
      (get-descriptor client fully-qualified-proto-name))
  

• deserialize (client proto-class-name data)

  Returns Clojure map for the given protobuf encoded byte array and protobuf class name.

  Argument list :

  Key	Type	Description
  client	Object	Instantiated Clojure client object
  proto-class-name	String	Name of the proto class whose proto descriptor object is required
  data	Byte-Array	Data (byte-array) to be deserialized using proto-descriptor object

  Response structure

  Value	Type	Description
  deserialized-message	PersistentArrayMap	Deserialized message (Clojure Map)

  Example:

  (let [client (create-client sample-client-config)
        proto-package "io.odpf.stencil_clj_test"
        proto-class-name "Scalar"
        fully-qualified-proto-name (str proto-package "." proto-class-name)
        proto-desc (get-descriptor client fully-qualified-proto-name)
        data-to-deserialize (serialize client fully-qualified-proto-name{:field-one 1.25})]
       (deserialize client fully-qualified-proto-name data-to-deserialize))
  

• serialize (client proto-class-name map)

  Returns protobuf encoded byte array for the given Clojure and protobuf class name.

  Argument list :

  Key	Type	Description
  client	Object	Instantiated Clojure client object
  proto-class-name	String	Name of the proto class whose proto descriptor object is required
  map	PersistentArrayMap	Data (in the form of map) to be serialized using proto descriptor object

  Response structure

  Value	Type	Description
  serialized-message	Byte-Array	Serialized message (byte-array)

  Example:

  (let [client (create-client sample-client-config)
        proto-package "io.odpf.stencil_clj_test"
        proto-class-name "Scalar"
        fully-qualified-proto-name (str proto-package "." proto-class-name)
        proto-desc (get-descriptor client fully-qualified-proto-name)]
       (serialize client fully-qualified-proto-name {:field-one 1.25}))
  

Development

• Ensure leiningen is installed.

• Run tests: lein clean && lein javac && lein test

• Run formatting: lein cljfmt fix