[BUG] Fix upload attachment

lib/features/composer/data/network/composer_api.dart

@@ -1,7 +1,9 @@
 
+import 'dart:convert';
 import 'dart:io';
 
 import 'package:core/core.dart';
+import 'package:dio/dio.dart';
 import 'package:model/model.dart';
 
 class ComposerAPI {
@@ -11,9 +13,15 @@ class ComposerAPI {
   ComposerAPI(this._dioClient);
 
   Future<UploadResponse> uploadAttachment(UploadRequest uploadRequest) async {
+    final file = File(uploadRequest.fileInfo.filePath);
+    final headerParam = _dioClient.getHeaders();
+    headerParam[HttpHeaders.contentTypeHeader] = uploadRequest.fileInfo.mimeType;
+    headerParam[HttpHeaders.contentLengthHeader] = file.readAsBytesSync().length;
+
     final resultJson = await _dioClient.post(
         Uri.decodeFull(uploadRequest.uploadUrl.toString()),
-        data: File(uploadRequest.fileInfo.filePath).readAsBytesSync());
-    return UploadResponse.fromJson(resultJson);
+        options: Options(headers: headerParam),
+        data: file.openRead());
+    return UploadResponse.fromJson(jsonDecode(resultJson));
   }
 }