Add source/read-uri-json multimethod.

Issue #44 - Add read-uri-json multimethod which dispatches on the URI
scheme. Add implementions for HTTP(S) and file schemes and raise an
error in the default implementation. Delegate to this method within
the URI implementation of JSONSource.

src/csv2rdf/source.clj

@@ -4,7 +4,8 @@
  [csv2rdf.util :as util]
  [clojure.spec.alpha :as s]
  [csv2rdf.http :as http]
- [clojure.data.json :as json])
+ [clojure.data.json :as json]
+ [clojure.string :as string])
  (:import [java.net URI]
  [java.io File InputStream ByteArrayInputStream]))
 
@@ -29,13 +30,29 @@
  (with-open [r (io/reader source)]
  (json/read r)))
 
+(defn- http-get-json [uri]
+ (let [{:keys [body]} (http/get-uri uri)]
+ (get-json body)))
+
+(defmulti read-uri-json
+ "Reads a JSON document from a URI"
+ (fn [^URI uri] (keyword (.getScheme uri))))
+
+(defmethod read-uri-json :file [uri] (read-json uri))
+(defmethod read-uri-json :http [uri] (http-get-json uri))
+(defmethod read-uri-json :https [uri] (http-get-json uri))
+(defmethod read-uri-json :default [uri]
+ (let [supported-schemes (keys (dissoc (methods read-uri-json) :default))]
+ (throw (ex-info
+ (format "Unable to read JSON from URI %s: unsupported scheme.%nSupported schemes: %s"
+ uri
+ (string/join ", " (map name supported-schemes)))
+ {:type ::unsupported-uri-scheme-error
+ :uri uri}))))
+
 (extend-protocol JSONSource
  URI
- (get-json [uri]
- (if (= (keyword (.getScheme uri)) :file)
- (read-json uri)
- (let [{:keys [body]} (http/get-uri uri)]
- (get-json body))))
+ (get-json [uri] (read-uri-json uri))
 
  File
  (get-json [f] (read-json f))

test/csv2rdf/source_test.clj

@@ -3,9 +3,10 @@
  [clojure.java.io :as io]
  [clojure.test :refer :all]
  [csv2rdf.http :as http]
- [csv2rdf.source :refer :all]
+ [csv2rdf.source :refer :all :as source]
  [csv2rdf.test-common :refer [->TestHttpClient]])
- (:import java.net.URI))
+ (:import java.net.URI
+ [clojure.lang ExceptionInfo]))
 
 (deftest get-json-test
  (testing "URI"
@@ -17,8 +18,17 @@
  (->TestHttpClient requests)
  (let [result (get-json uri)]
  (is (= json result))))))
+
  (testing "file scheme"
  (let [uri (.toURI (io/file "w3c-csvw/tests/test104.json"))
  json {}
  result (get-json uri)]
- (is (= json result))))))
+ (is (= json result))))
+
+ (testing "unsupported scheme"
+ (let [uri (URI. "unsupported:example.com")]
+ (try
+ (get-json uri)
+ (is false "Expected exception to be thrown")
+ (catch ExceptionInfo ex
+ (is (= ::source/unsupported-uri-scheme-error (:type (ex-data ex))))))))))