Normalize all headers into lowercase

src/main/ua-parser.js

@@ -1390,11 +1390,20 @@
             extensions = undefined;
         }
 
+        if (headers) {
+            if (typeof headers.append === FUNC_TYPE) {
                 // Convert Headers object into a plain object
-        if (headers && typeof headers.append === FUNC_TYPE) {
                 var kv = {};
-            headers.forEach(function (v, k) { kv[k] = v; });
+                headers.forEach(function (v, k) { kv[String(k).toLowerCase()] = v; });
                 headers = kv;
+            } else {
+                // Normalize headers field name into lowercase
+                var normalized = {};
+                for (var header in headers) {
+                    normalized[String(header).toLowerCase()] = headers[header];
+                }
+                headers = normalized;
+            }
         }
         
         if (!(this instanceof UAParser)) {

test/unit/main.js

@@ -381,4 +381,12 @@ describe('Read user-agent data from req.headers', function () {
         const { browser } = UAParser(reqHeaders);
         assert.strictEqual(browser.is('Midori'), true);
     });
+
+    it('Headers field name should be case insensitive', function () {    
+        const hEaDeRs = {
+            'uSeR-aGenT' : 'Midori/0.2.2 (X11; Linux i686; U; en-us) WebKit/531.2+'
+        };
+        const { browser } = UAParser(hEaDeRs);
+        assert.strictEqual(browser.toString(), "Midori 0.2.2");
+    });
 });