fix($http): ensure case-insens. header overriding

If user send content-type header, both content-type and default
Content-Type headers were sent. Now default header overriding is
case-insensitive.

src/ng/http.js

@@ -649,17 +649,12 @@ function $HttpProvider() {
         transformRequest: defaults.transformRequest,
         transformResponse: defaults.transformResponse
       };
-      var headers = {};
+      var headers = mergeHeaders(requestConfig);
 
       extend(config, requestConfig);
       config.headers = headers;
       config.method = uppercase(config.method);
 
-      extend(headers,
-          defaults.headers.common,
-          defaults.headers[lowercase(config.method)],
-          requestConfig.headers);
-
       var xsrfValue = isSameDomain(config.url, $browser.url())
           ? $browser.cookies()[config.xsrfCookieName || defaults.xsrfCookieName]
           : undefined;
@@ -673,7 +668,11 @@ function $HttpProvider() {
 
         // strip content-type if data is undefined
         if (isUndefined(config.data)) {
-          delete headers['Content-Type'];
+          forEach(headers, function(value, header) {
+            if (lowercase(header) === 'content-type') {
+                delete headers[header];
+            }
+          });
         }
 
         if (isUndefined(config.withCredentials) && !isUndefined(defaults.withCredentials)) {
@@ -729,6 +728,30 @@ function $HttpProvider() {
           ? resp
           : $q.reject(resp);
       }
+
+      function mergeHeaders(config) {
+        var defHeaders = defaults.headers,
+            reqHeaders = extend({}, config.headers),
+            defHeaderName, lowercaseDefHeaderName, reqHeaderName;
+
+        defHeaders = extend({}, defHeaders.common, defHeaders[lowercase(config.method)]);
+
+        // using for-in instead of forEach to avoid unecessary iteration after header has been found
+        defaultHeadersIteration:
+        for (defHeaderName in defHeaders) {
+          lowercaseDefHeaderName = lowercase(defHeaderName);
+
+          for (reqHeaderName in reqHeaders) {
+            if (lowercase(reqHeaderName) === lowercaseDefHeaderName) {
+              continue defaultHeadersIteration;
+            }
+          }
+
+          reqHeaders[defHeaderName] = defHeaders[defHeaderName];
+        }
+
+        return reqHeaders;
+      }
     }
 
     $http.pendingRequests = [];

test/ng/httpSpec.js

@@ -717,6 +717,21 @@ describe('$http', function() {
         $httpBackend.flush();
       });
 
+      it('should override default headers with custom in a case insensitive manner', function() {
+        $httpBackend.expect('POST', '/url', 'messageBody', function(headers) {
+          return headers['accept'] == 'Rewritten' &&
+                 headers['content-type'] == 'Content-Type Rewritten' &&
+                 headers['Accept'] === undefined &&
+                 headers['Content-Type'] === undefined;
+        }).respond('');
+
+        $http({url: '/url', method: 'POST', data: 'messageBody', headers: {
+          'accept': 'Rewritten',
+          'content-type': 'Content-Type Rewritten'
+        }});
+        $httpBackend.flush();
+      });
+
       it('should not set XSRF cookie for cross-domain requests', inject(function($browser) {
         $browser.cookies('XSRF-TOKEN', 'secret');
         $browser.url('http://host.com/base');
@@ -734,7 +749,12 @@ describe('$http', function() {
           return !headers.hasOwnProperty('Content-Type');
         }).respond('');
 
+        $httpBackend.expect('POST', '/url2', undefined, function(headers) {
+          return !headers.hasOwnProperty('content-type');
+        }).respond('');
+        
         $http({url: '/url', method: 'POST'});
+        $http({url: '/url2', method: 'POST', headers: {'content-type': 'Rewritten'}});
         $httpBackend.flush();
       });