diff --git a/.github/stale.yml b/.github/stale.yml
index 3b3b587f7..470dec312 100644
--- a/.github/stale.yml
+++ b/.github/stale.yml
@@ -5,6 +5,7 @@ daysUntilClose: 7
 # Issues with these labels will never be considered stale
 exemptLabels:
   - important
+  - pinned
 # Label to use when marking an issue as stale
 staleLabel: stale
 # Comment to post when marking an issue as stale. Set to `false` to disable
diff --git a/dio/lib/src/adapters/browser_adapter.dart b/dio/lib/src/adapters/browser_adapter.dart
index fdd50b538..6806ab305 100644
--- a/dio/lib/src/adapters/browser_adapter.dart
+++ b/dio/lib/src/adapters/browser_adapter.dart
@@ -47,7 +47,7 @@ class BrowserHttpClientAdapter implements HttpClientAdapter {
             body,
             xhr.status,
             headers: xhr.responseHeaders
-                .map((k, v) => MapEntry(k.toLowerCase(), v.split(','))),
+                .map((k, v) => MapEntry(k, v.split(','))),
             statusMessage: xhr.statusText,
             isRedirect: xhr.status == 302 || xhr.status == 301,
           ),
diff --git a/dio/lib/src/adapters/io_adapter.dart b/dio/lib/src/adapters/io_adapter.dart
index f2b1c0cd0..6071aa6e0 100644
--- a/dio/lib/src/adapters/io_adapter.dart
+++ b/dio/lib/src/adapters/io_adapter.dart
@@ -86,7 +86,8 @@ class DefaultHttpClientAdapter implements HttpClientAdapter {
       stream,
       responseStream.statusCode,
       headers: headers,
-      isRedirect: responseStream.isRedirect||responseStream.redirects.isNotEmpty,
+      isRedirect:
+          responseStream.isRedirect || responseStream.redirects.isNotEmpty,
       redirects: responseStream.redirects
           .map((e) => RedirectRecord(e.statusCode, e.method, e.location))
           .toList(),
@@ -100,6 +101,7 @@ class DefaultHttpClientAdapter implements HttpClientAdapter {
         : null;
     if (cancelFuture != null) {
       var _httpClient = HttpClient();
+      _httpClient.userAgent = null;
       if (onHttpClientCreate != null) {
         //user can return a HttpClient instance
         _httpClient = onHttpClientCreate(_httpClient) ?? _httpClient;
diff --git a/dio/lib/src/dio.dart b/dio/lib/src/dio.dart
index a64df98c2..6120dea2e 100644
--- a/dio/lib/src/dio.dart
+++ b/dio/lib/src/dio.dart
@@ -862,16 +862,19 @@ abstract class DioMixin implements Dio {
     // Convert the error interceptor to a functional callback in which
     // we can handle the return value of interceptor callback.
     Function _errorInterceptorWrapper(errInterceptor) {
-      return (err) async {
-        if (err is! Response) {
-          var _e = await errInterceptor(assureDioError(err, requestOptions));
-          if (_e is! Response) {
-            throw assureDioError(_e ?? err, requestOptions);
+      return (err) {
+        return checkIfNeedEnqueue(interceptors.errorLock, (){
+          if (err is! Response) {
+            return errInterceptor(assureDioError(err, requestOptions)).then((e){
+              if (e is! Response) {
+                throw assureDioError(e ?? err, requestOptions);
+              }
+              return e;
+            });
           }
-          err = _e;
-        }
-        // err is a Response instance
-        return err;
+          // err is a Response instance
+          return err;
+        });
       };
     }
 
@@ -1032,7 +1035,8 @@ abstract class DioMixin implements Dio {
         options.headers[Headers.contentLengthHeader] = length.toString();
       }
       var complete = 0;
-      var byteStream = stream.transform<Uint8List>(StreamTransformer.fromHandlers(
+      var byteStream =
+          stream.transform<Uint8List>(StreamTransformer.fromHandlers(
         handleData: (data, sink) {
           if (options.cancelToken != null && options.cancelToken.isCancelled) {
             sink
diff --git a/dio/lib/src/interceptors/log.dart b/dio/lib/src/interceptors/log.dart
index 458d366c5..82e3dce6a 100644
--- a/dio/lib/src/interceptors/log.dart
+++ b/dio/lib/src/interceptors/log.dart
@@ -53,23 +53,23 @@ class LogInterceptor extends Interceptor {
   @override
   Future onRequest(RequestOptions options) async {
     logPrint('*** Request ***');
-    printKV('uri', options.uri);
+    _printKV('uri', options.uri);
 
     if (request) {
-      printKV('method', options.method);
-      printKV('responseType', options.responseType?.toString());
-      printKV('followRedirects', options.followRedirects);
-      printKV('connectTimeout', options.connectTimeout);
-      printKV('receiveTimeout', options.receiveTimeout);
-      printKV('extra', options.extra);
+      _printKV('method', options.method);
+      _printKV('responseType', options.responseType?.toString());
+      _printKV('followRedirects', options.followRedirects);
+      _printKV('connectTimeout', options.connectTimeout);
+      _printKV('receiveTimeout', options.receiveTimeout);
+      _printKV('extra', options.extra);
     }
     if (requestHeader) {
       logPrint('headers:');
-      options.headers.forEach((key, v) => printKV(' $key', v));
+      options.headers.forEach((key, v) => _printKV(' $key', v));
     }
     if (requestBody) {
       logPrint('data:');
-      printAll(options.data);
+      _printAll(options.data);
     }
     logPrint('');
   }
@@ -94,29 +94,29 @@ class LogInterceptor extends Interceptor {
   }
 
   void _printResponse(Response response) {
-    printKV('uri', response.request?.uri);
+    _printKV('uri', response.request?.uri);
     if (responseHeader) {
-      printKV('statusCode', response.statusCode);
+      _printKV('statusCode', response.statusCode);
       if (response.isRedirect == true) {
-        printKV('redirect', response.realUri);
+        _printKV('redirect', response.realUri);
       }
       if (response.headers != null) {
         logPrint('headers:');
-        response.headers.forEach((key, v) => printKV(' $key', v.join(',')));
+        response.headers.forEach((key, v) => _printKV(' $key', v.join(',')));
       }
     }
     if (responseBody) {
       logPrint('Response Text:');
-      printAll(response.toString());
+      _printAll(response.toString());
     }
     logPrint('');
   }
 
-  void printKV(String key, Object v) {
+  void _printKV(String key, Object v) {
     logPrint('$key: $v');
   }
 
-  void printAll(msg) {
+  void _printAll(msg) {
     msg.toString().split('\n').forEach(logPrint);
   }
 }
diff --git a/dio/lib/src/options.dart b/dio/lib/src/options.dart
index 9411ebd86..f4b25cea6 100644
--- a/dio/lib/src/options.dart
+++ b/dio/lib/src/options.dart
@@ -137,7 +137,7 @@ class BaseOptions extends _RequestConfig {
 
 /// Every request can pass an [Options] object which will be merged with [Dio.options]
 class Options extends _RequestConfig {
-  Options({
+ Options({
     String method,
     int sendTimeout,
     int receiveTimeout,
@@ -350,8 +350,6 @@ class _RequestConfig {
     this.headers = headers ?? {};
     this.extra = extra ?? {};
     this.contentType = contentType;
-    this.headers =
-        this.headers.map((key, v) => MapEntry(key.toLowerCase().toString(), v));
   }
 
   /// Http method.
@@ -380,7 +378,7 @@ class _RequestConfig {
   /// you can set `ContentType.parse('application/x-www-form-urlencoded')`, and [Dio]
   /// will automatically encode the request body.
   set contentType(String contentType) {
-    headers[Headers.contentTypeHeader] = contentType?.toLowerCase()?.trim();
+    headers[Headers.contentTypeHeader] = contentType?.trim();
   }
 
   String get contentType => headers[Headers.contentTypeHeader];
diff --git a/dio/pubspec.yaml b/dio/pubspec.yaml
index 4b2704ca0..61b8d8b3e 100644
--- a/dio/pubspec.yaml
+++ b/dio/pubspec.yaml
@@ -14,6 +14,6 @@ dev_dependencies:
   test: ^1.5.1
   pedantic: ^1.8.0
   test_coverage: ^0.4.1
-  flutter_test:
-    sdk: flutter
+#  flutter_test:
+#    sdk: flutter
 
diff --git a/dio/test/interceptor_test.dart b/dio/test/interceptor_test.dart
index 40625940e..f2821fcd4 100644
--- a/dio/test/interceptor_test.dart
+++ b/dio/test/interceptor_test.dart
@@ -109,7 +109,7 @@ void main() {
         throwsA(equals('custom error info [404]')));
   });
 
-  group('Interceptor lock', () {
+  group('Interceptor request lock', () {
     test('test', () async {
       String csrfToken;
       Dio dio = Dio();
@@ -153,4 +153,61 @@ void main() {
       assert(dio.interceptors.isEmpty == true);
     });
   });
+
+  group('Interceptor error lock', () {
+    test('test', () async {
+      String csrfToken;
+      Dio dio = Dio();
+      int tokenRequestCounts = 0;
+      // dio instance to request token
+      Dio tokenDio = Dio();
+      dio.options.baseUrl = tokenDio.options.baseUrl = MockAdapter.mockBase;
+      dio.httpClientAdapter = tokenDio.httpClientAdapter = MockAdapter();
+      dio.interceptors.add(InterceptorsWrapper(onRequest: (opt) {
+        opt.headers["csrfToken"] = csrfToken;
+      }, onError: (DioError error) {
+        // Assume 401 stands for token expired
+        if (error.response?.statusCode == 401) {
+          RequestOptions options = error.response.request;
+          // If the token has been updated, repeat directly.
+          if (csrfToken != options.headers["csrfToken"]) {
+            options.headers["csrfToken"] = csrfToken;
+            //repeat
+            return dio.request(options.path, options: options);
+          }
+          // update token and repeat
+          // Lock to block the incoming request until the token updated
+          dio.lock();
+          dio.interceptors.responseLock.lock();
+          dio.interceptors.errorLock.lock();
+          tokenRequestCounts++;
+          return tokenDio.get("/token").then((d) {
+            //update csrfToken
+            options.headers["csrfToken"] = csrfToken = d.data['data']['token'];
+          }).whenComplete(() {
+            dio.unlock();
+            dio.interceptors.responseLock.unlock();
+            dio.interceptors.errorLock.unlock();
+          }).then((e) {
+            //repeat
+            return dio.request(options.path, options: options);
+          });
+        }
+        return error;
+      }));
+
+      int result = 0;
+      _onResult(d) {
+        if (tokenRequestCounts > 0) ++result;
+      }
+
+      await Future.wait([
+        dio.get('/test-auth?tag=1').then(_onResult),
+        dio.get('/test-auth?tag=2').then(_onResult),
+        dio.get('/test-auth?tag=3').then(_onResult)
+      ]);
+      expect(tokenRequestCounts, 1);
+      expect(result, 3);
+    });
+  });
 }
diff --git a/dio/test/mock_adapter.dart b/dio/test/mock_adapter.dart
index 11c92b41b..fa72bc49b 100644
--- a/dio/test/mock_adapter.dart
+++ b/dio/test/mock_adapter.dart
@@ -27,6 +27,35 @@ class MockAdapter extends HttpClientAdapter {
               Headers.contentTypeHeader: [Headers.jsonContentType],
             },
           );
+          break;
+        case "/test-auth":
+          {
+            return Future.delayed(Duration(milliseconds: 300), () {
+              if (options.headers['csrfToken'] == null) {
+                return ResponseBody.fromString(
+                  jsonEncode({
+                    "errCode": -1,
+                    "data": {"path": uri.path}
+                  }),
+                  401,
+                  headers: {
+                    Headers.contentTypeHeader: [Headers.jsonContentType],
+                  },
+                );
+              }
+              return ResponseBody.fromString(
+                jsonEncode({
+                  "errCode": 0,
+                  "data": {"path": uri.path}
+                }),
+                200,
+                headers: {
+                  Headers.contentTypeHeader: [Headers.jsonContentType],
+                },
+              );
+            });
+          }
+          break;
         case "/download":
           return Future.delayed(Duration(milliseconds: 300), () {
             return ResponseBody(
diff --git a/example/dio.dart b/example/dio.dart
index e435b3536..7e5145ceb 100644
--- a/example/dio.dart
+++ b/example/dio.dart
@@ -13,6 +13,7 @@ main() async {
     ..headers = {
       HttpHeaders.userAgentHeader: 'dio',
       'common-header': 'xx',
+      'Common-header': 'xx',
     };
 
 // Or you can create dio instance and config it as follow:
diff --git a/example/interceptor_lock.dart b/example/interceptor_lock.dart
index 628bc92ec..88de37105 100644
--- a/example/interceptor_lock.dart
+++ b/example/interceptor_lock.dart
@@ -9,7 +9,8 @@ main() async {
   String csrfToken;
   dio.options.baseUrl = "http://www.dtworkroom.com/doris/1/2.0.0/";
   tokenDio.options = dio.options;
-  dio.interceptors.add(InterceptorsWrapper(onRequest: (RequestOptions options) {
+  dio.interceptors.add(InterceptorsWrapper(
+      onRequest: (RequestOptions options) {
     print('send request：path:${options.path}，baseURL:${options.baseUrl}');
     if (csrfToken == null) {
       print("no token，request token firstly...");
diff --git a/example/test.dart b/example/test.dart
index 74f52dd6c..f4c24e2ea 100644
--- a/example/test.dart
+++ b/example/test.dart
@@ -4,24 +4,22 @@ void getHttp() async {
   var dio = Dio();
   dio.interceptors.add(LogInterceptor(responseBody: true));
   dio.options.baseUrl = "http://httpbin.org";
+  dio.options.headers=   {
+  'Authorization': 'Bearer '
+  };
   //dio.options.baseUrl = "http://localhost:3000";
-  dio.options.receiveDataWhenStatusError=false;
-  dio.interceptors.add(InterceptorsWrapper(onResponse: (r){
-    //throw DioError(...); or
-    return dio.reject("xxx");
-  }));
-  try {
-    await Future.wait([
-      dio.get("/get", queryParameters: {"id": 1}),
-      dio.get("/get", queryParameters: {"id": 2})
-    ]);
-  } catch (e) {
-    print(e);
-  }
+  var response=await dio.post("/post",data:null,
+      options: Options(contentType: Headers.jsonContentType, headers: {"Content-Type": "application/json"})
+  );
+  print(response);
 }
 
 main() async {
-  await getHttp();
+  //await getHttp();
+
+  var response = await Dio().get("http://flutterchina.club");
+  print(response.isRedirect);
+
 //  var t = await MultipartFile.fromBytes([5]);
 //  print(t);
 }