Ensure :headers is according to Ring spec

Fixes the issue #3

Author: viesti

src/fierycod/holy_lambda_ring_adapter/core.cljc

@@ -33,7 +33,12 @@
   [{:keys [event ctx]}]
   (let [request-ctx (get event :requestContext)
         http        (get request-ctx :http)
-        headers     (get event :headers)
+        headers     (persistent! (reduce (fn [acc [k v]]
+                                           (if (keyword? k)
+                                             (assoc! acc (.toLowerCase (name k)) v)
+                                             (assoc! acc k v)))
+                                         (transient {})
+                                         (get event :headers)))
         base64?     (get event :isBase64Encoded)]
     (when-not request-ctx
       (throw (ex-info "Incorrect shape of AWS event. The adapter is compatible with following integrations: HttpApi and RestApi on AWS Api Gateway service. If you're testing locally make sure the event shape is valid e.g. use `sam local start-api` instead of `sam local invoke`." {:ctx :hl-ring-adapter})))

test/fierycod/holy_lambda_ring_adapter/core_test.clj

@@ -202,7 +202,15 @@
                 :body            "hello world HTTP/1.1",
                 :isBase64Encoded false,
                 :headers         {"something" "something"}}
-               ((hra/ring<->hl-middleware basic-ring-handler-async) request2 identity identity))))))
+               ((hra/ring<->hl-middleware basic-ring-handler-async) request2 identity identity)))))
+
+  (t/testing "Ensure :headers is a map of downcase strings as keys"
+    (t/is (= {"content-type" "application/json"}
+             (:headers (request->ring-request-test {:event {:path "/foo"
+                                                            :isBase64Encoded false
+                                                            :headers {:Content-Type "application/json"}
+                                                            :requestContext {:httpMethod "GET"}}
+                                                    :ctx nil}))))))
 
 (t/deftest http-api-json-coerce-1
   (t/testing "json coercion should work"