fix: websocket multi-value connection upgrades

Fixes an issue where browsers could send `keep-alive` and `Upgrade` in
the same request causing the `ws/upgrade-request?` to return false.

ring-core/src/ring/websocket.clj

@@ -67,7 +67,7 @@
   "Returns true if the request map is a websocket upgrade request."
   [request]
   (let [headers (:headers request)]
-    (and (.equalsIgnoreCase "upgrade" (get headers "connection"))
+    (and (re-find #"\b(?i)upgrade\b" (get headers "connection"))
          (.equalsIgnoreCase "websocket" (get headers "upgrade")))))
 
 (defn websocket-response?

ring-core/test/ring/test/websocket.clj

@@ -3,6 +3,14 @@
             [ring.websocket :as ws]
             [ring.websocket.protocols :as wsp]))
 
+
+(deftest test-upgrade-request?
+  (is (not (ws/upgrade-request? {})))
+  (is (ws/upgrade-request? {:headers {"connection" "Upgrade"
+                                      "upgrade"    "websocket"}}))
+  (is (ws/upgrade-request? {:headers {"connection" "keep-alive, Upgrade"
+                                      "upgrade"    "websocket"}})))
+
 (deftest test-request-protocols
   (is (empty? (ws/request-protocols {:headers {}})))
   (is (= ["mqtt"]