Swagger Spec for Clojure Web Apps
Clojure Shell
Latest commit a338279 Jan 11, 2017 @miikka miikka Version 0.22.15-SNAPSHOT


Ring-Swagger Build Status Downloads Dependencies Status

Swagger 2.0 implementation for Clojure/Ring using Plumatic Schema (support for clojure.spec is coming up).

  • Transforms deeply nested Schemas into Swagger JSON Schema definitions
  • Extended & symmetric JSON & String serialization & coercion
  • Middleware for handling Schemas Validation Errors & Publishing swagger-data
  • Local api validator
  • Swagger artifact generation

Latest version

Clojars Project

Web libs using Ring-Swagger

Getting help

Clojurians slack (join) has a channel #ring-swagger for Ring-swagger related issues. You can also ask questions about Ring-swagger on other channels at Clojurians Slack or at #clojure on Freenode IRC (mention or ring-swagger to highlight us).


Route definitions are expected as a clojure Map defined by the Schema Contract. The Schema allows mostly any extra keys as ring-swagger tries not to be on your way - one can pass any valid Swagger spec data in.

API Docs.

Simplest possible example

(require '[ring.swagger.swagger2 :as rs])

(rs/swagger-json {})

; {:swagger "2.0",
;  :info {:title "Swagger API", :version "0.0.1"},
;  :produces ["application/json"],
;  :consumes ["application/json"],
;  :paths {},
;  :definitions {}}

More complete example

Info, tags, routes and anonymous nested schemas.

(require '[schema.core :as s])

(s/defschema User {:id s/Str, 
                   :name s/Str
                   :address {:street s/Str
                             :city (s/enum :tre :hki)}})

    {:info {:version "1.0.0"
            :title "Sausages"
            :description "Sausage description"
            :termsOfService "http://helloreverb.com/terms/"
            :contact {:name "My API Team"
                      :email "foo@example.com"
                      :url "http://www.metosin.fi"}
            :license {:name "Eclipse Public License"
                      :url "http://www.eclipse.org/legal/epl-v10.html"}}
     :tags [{:name "user"
             :description "User stuff"}]
     :paths {"/api/ping" {:get {}}
             "/user/:id" {:post {:summary "User Api"
                                  :description "User Api description"
                                  :tags ["user"]
                                  :parameters {:path {:id s/Str}
                                               :body User}
                                  :responses {200 {:schema User
                                                   :description "Found it!"}
                                              404 {:description "Ohnoes."}}}}}}))

; {:swagger "2.0",
;  :info {:title "Sausages",
;         :version "1.0.0",
;         :description "Sausage description",
;         :termsOfService "http://helloreverb.com/terms/",
;         :contact {:name "My API Team",
;                   :email "foo@example.com",
;                   :url "http://www.metosin.fi"},
;         :license {:name "Eclipse Public License",
;                   :url "http://www.eclipse.org/legal/epl-v10.html"}},
;  :produces ["application/json"],
;  :consumes ["application/json"],
;  :tags [{:name "user", :description "User stuff"}],
;  :paths {"/api/ping" {:get {:responses {:default {:description ""}}}},
;          "/user/{id}" {:post {:summary "User Api",
;                               :description "User Api description",
;                               :tags ["user"],
;                               :parameters [{:in "path",
;                                             :name "id",
;                                             :description "",
;                                             :required true,
;                                             :type "string"}
;                                            {:in "body",
;                                             :name "User",
;                                             :description "",
;                                             :required true,
;                                             :schema {:$ref "#/definitions/User"}}],
;                               :responses {200 {:schema {:$ref "#/definitions/User"},
;                                                         :description "Found it!"},
;                                           404 {:description "Ohnoes."}}}}},
;  :definitions {"User" {:type "object",
;                        :properties {:id {:type "string"},
;                                     :name {:type "string"},
;                                     :address {:$ref "#/definitions/UserAddress"}},
;                        :additionalProperties false,
;                        :required (:id :name :address)},
;                "UserAddress" {:type "object",
;                               :properties {:street {:type "string"},
;                                                     :city {:type "string",
;                                                            :enum (:tre :hki)}},
;                               :additionalProperties false,
;                               :required (:street :city)}}}

producing the following ui:


Customizing Swagger Spec output

One can pass extra options-map as a third parameter to swagger-json. The following options are available:

 :ignore-missing-mappings?        - (false) boolean whether to silently ignore
                                    missing schema to JSON Schema mappings. if
                                    set to false, IllegalArgumentException is
                                    thrown if a Schema can't be presented as
                                    JSON Schema.

 :default-response-description-fn - ((constantly "")) - a fn to generate default
                                    response descriptions from http status code.
                                    Takes a status code (Int) and returns a String.

 :handle-duplicate-schemas-fn     - (ring.swagger.core/ignore-duplicate-schemas),
                                    a function to handle possible duplicate schema
                                    definitions. Takes schema-name and set of found
                                    attached schema values as parameters. Returns
                                    sequence of schema-name and selected schema value.

 :collection-format               - Sets the collectionFormat for query and formData
                                    Possible values: multi, ssv, csv, tsv, pipes."

For example, to get default response descriptions from the HTTP Spec, you can do the following:

(require '[ring.util.http-status :as status])

  {:paths {"/hello" {:post {:responses {200 nil
                                        425 nil
                                        500 {:description "FAIL"}}}}}}
  {:default-response-description-fn status/get-description})

; {:swagger "2.0"
;  :info {:title "Swagger API" :version "0.0.1"}
;  :consumes ["application/json"]
;  :produces ["application/json"]
;  :definitions {}
;  :paths {"/hello" {:post {:responses {200 {:description "OK"}
;                                       425 {:description "The collection is unordered."}
;                                       500 {:description "FAIL"}}}}}}

Validating the Swagger Spec

The generated full spec can be validated against the Swagger JSON Schema with the help of scjsv.

(require '[ring.swagger.validator :as v])

(v/validate (rs/swagger-json {:paths {"/api/ping" {:get nil}}}))
; nil

(v/validate (rs/swagger-json {:pathz {"/api/ping" {:get nil}}}))
; ({:level "error"
;   :schema {:loadingURI "#", :pointer ""}
;   :instance {:pointer ""}
;   :domain "validation"
;   :keyword "additionalProperties"
;   :message "object instance has properties which are not allowed by the schema: [\"pathz\"]", :unwanted ["pathz"]})

For more information about creating your own adapter, see Collecting API Documentation.

Transforming the Swagger Spec

There are the following utility functions for transforming the spec (on the client side):

ring.swagger.swagger2/transform-operations - transforms the operations under the :paths of a ring-swagger spec by applying (f operation) to all operations. If the function returns nil, the given operation is removed.

As an example, one can filter away all operations with :x-no-doc set to true:

(defn remove-x-no-doc [endpoint]
  (if-not (some-> endpoint :x-no-doc true?)

(transform-operations remove-x-no-doc {:paths {"/a" {:get {:x-no-doc true}, :post {}}
                                               "/b" {:put {:x-no-doc true}}}}))
; {:paths {"/a" {:post {}}}}

Web Schemas

Prismatic Schema is used to describe both the input & output schemas for routes.

As Swagger 2.0 Spec Schema is a deterministic subset of JSON Schema, so not all Clojure Schema elements can be used.

Schema to Swagger JSON Schema conversion

There are two possible methods to do this:

  1. class-based dispatch via ring.swagger.json-schema/convert-class.
  2. protocol-based dispatch via ring.swagger.json-schema/JsonSchema - the convert fn.

Both take the Schema and swagger options map as arguments. Options contain also :in to denote the possible location of the schema (nil, :query, :header, :path, :formData and :body).

To support truly symmetric web schemas, one needs also to ensure both JSON Serialization and deserialization/coercion from JSON.

Class-based dispatch

(require '[ring.swagger.json-schema :as json-schema])

(defmethod json-schema/convert-class java.sql.Date [_ _] {:type "string" :format "date"})

Protocol-based dispatch

(require '[ring.swagger.json-schema :as json-schema])

(extend-type java.util.regex.Pattern
  (json-schema/convert [e _] 
    {:type "string" :pattern (str e)}))

One can also use the options to create more accurate specs (via the :in option).

(extend-type schema.core.Maybe
  (convert [e {:keys [in]}]
    (let [schema (->swagger (:schema e))]
      (if (#{:query :formData} in)
        (assoc schema :allowEmptyValue true)

Out-of-the-box supported Schema elements

Clojure Schema JSON Schema Sample JSON
Integer integer, int32 1
Long, s/Int integer, int64 1
Double, Number, s/Num number, double 1.2
String, s/Str, Keyword, s/Keyword, Symbol, s/Symbol, s/Any non-body-parameter string "kikka"
Boolean boolean true
nil, s/Any body-parameter void
java.util.Date, org.joda.time.DateTime, s/Inst string, date-time "2014-02-18T18:25:37.456Z", also without millis: "2014-02-18T18:25:37Z"
java.util.regex.Pattern, string, regex [a-z0-9]
#"[a-z0-9]+" string, pattern "a6"
s/Uuid, java.util.UUID string, uuid "77e70512-1337-dead-beef-0123456789ab"
org.joda.time.LocalDate string, date "2014-02-19"
org.joda.time.LocalTime string, time "16:22"
(s/enum X Y Z) type of X, enum(X,Y,Z)
(s/maybe X) type of X
(s/both X Y Z) type of X
(s/constrained X pred) type of X
(s/conditional p1 X p2 Y p3 Z) one of type X, Y, Z
(s/cond-pre X Y Z) one of type X, Y, Z
(s/either X Y Z) type of X
(s/named X name) type of X
(s/one X name) type of X
(s/recursive Var) Ref to (model) Var
(s/eq X) type of class of X
(s/optional-key X) optional key
(s/required-key X) required key
s/Keyword (as a key) ignored
  • All supported types have symmetric JSON serialization (Cheshire encoders) & deserialization (Schema coercions)
  • Vectors, Sets and Maps can be used as containers
  • Maps are presented as Complex Types and References. Model references are resolved automatically.
    • Nested maps are transformed automatically into flat maps with generated child references
    • Maps can be within valid containers (as only element - heterogeneous schema sequences not supported by the spec)

Missing Schema elements

If Ring-swagger can't transform the Schemas into JSON Schemas, by default a IllegalArgumentException will be thrown. Setting the :ignore-missing-mappings? to true causes the errors to be ignored - missing schema elements will be ignored from the generated Swagger schema.

Body and Response model names

Standard Prismatic Schema names are used. Nested schemas are traversed and all found sub-schemas are named automatically - so that they can be referenced in the generated Swagger spec.

Swagger 2.0 squashes all api models into a single global namespace, so schema name collisions can happen. When this happens, the function defined by :handle-duplicate-schemas-fn option is called to resolve the collision. By default, the collisions are ignored.

One accidental reason for schema name collisions is the use of normal clojure.core functions to create transformed copies of the schemas. The normal core functions retain the original schema meta-data and by so the schema name.

(s/defschema User {:id s/Str, :name s/Str})
(def NewUser (dissoc User :id)) ; dissoc does not remove the schema meta-data

(meta User)
; {:name User :ns user}

(meta NewUser)
; {:name User :ns user} <--- fail, now there are two User-schemas around.

There are better schema transformers functions available at schema-tools. It's an implicit dependency of ring-swagger.

Extra Schema elements supported by ring.swagger.json-schema-dirty

Some Schema elements are impossible to accurately describe within boundaries of JSON-Schema or Swagger spec. You can require ring.swagger.json-schema-dirty namespace to get JSON Schema dispatching for the following:

WARNING Swagger-UI might not display these correctly and the code generated by swagger-codegen will be inaccurate.

Clojure JSON Schema Sample
(s/conditional pred X pred Y pred Z) oneOf: type of X, type of Y, type of Z
(s/if pred X Y) oneOf: type of X, type of Y

Schema coercion

Ring-swagger uses Schema coercions for transforming the input data into vanilla Clojure and back.

There are two coercers in ring.swagger.coerce, the json-schema-coercion-matcher and query-schema-coercion-matcher. These are enchanced versions of the original Schema coercers, adding support for all the supported Schema elements, including Dates & Regexps.


Ring-swagger provides a convenience function for coercion, ring.swagger.schema/coerce!. It returns either a valid coerced value of slingshots an Map with type :ring.swagger.schema/validation. One can catch these exceptions via ring.swagger.middleware/wrap-validation-errors and return a JSON-friendly map of the contents.

(require '[schema.core :as s])
(require '[ring.swagger.schema :refer [coerce!]])

(s/defschema Bone {:size Long, :animal (s/enum :cow :tyrannosaurus)})

(coerce! Bone {:size 12, :animal "cow"})
; {:animal :cow, :size 12}

(coerce! Bone {:animal :sheep})
; ExceptionInfo throw+: #schema.utils.ErrorContainer{:error {:animal (not (#{:tyrannosaurus :cow} :sheep)), :size missing-required-key}, :type :ring.swagger.schema/validation}  ring.swagger.schema/coerce! (schema.clj:57)

Adding description to Schemas

One can add extra meta-data, including descriptions to schema elements using ring.swagger.json-schema/field and ring.swagger.json-schema/describe functions. These work by adding meta-data to schema under :json-schema-key. Objects which don't natively support meta-data, like Java classes, are wrapped automatically into ring.swagger.json-schema/FieldSchema to enable the meta-data.


(require '[schema.core :as s])
(require '[ring.swagger.schema :as rs])
(require '[ring.swagger.json-schema :as rjs])

(s/defschema Required
    {(s/optional-key :name) s/Str
     (s/optional-key :title) s/Str
     :address (rjs/field
                {:street (rsjs/field s/Str {:description "description here"})}
                {:description "Streename"
                 :example "Ankkalinna 1"})}
    {:minProperties 1
     :description "I'm required"
     :example {:name "Iines"
               :title "Ankka"}}))

; produces the following JSON Schema models =>
; {"Required" {:type "object"
;              :description "I'm required"
;              :example {:name "Iines"
;                        :title "Ankka"}
;              :minProperties 1
;              :required [:address]
;              :properties {:name {:type "string"}
;                           :title {:type "string"}
;                           :address {:$ref "#/definitions/RequiredAddress"}}
;              :additionalProperties false}
;  "RequiredAddress" {:type "object"
;                     :description "Streename"
;                     :example "Ankkalinna 1"
;                     :properties {:street {:type "string"
;                                           :description "description here"}}
;                     :required [:street]
;                     :additionalProperties false}}


Copyright © 2014-2016 Metosin Oy

Distributed under the Eclipse Public License, the same as Clojure.