Add response format option #122

src/android/src/main/java/com/RNFetchBlob/RNFetchBlobReq.java

         FileStorage
     }
 
+    enum ResponseFormat {
+        Auto,
+        UTF8,
+        BASE64
+    }
+
     public static HashMap<String, Call> taskTable = new HashMap<>();
     static HashMap<String, Boolean> progressReport = new HashMap<>();
     static HashMap<String, Boolean> uploadProgressReport = new HashMap<>();
     RNFetchBlobBody requestBody;
     RequestType requestType;
     ResponseType responseType;
+    ResponseFormat responseFormat = ResponseFormat.Auto;
     WritableMap respInfo;
     boolean timeout = false;
+
     ArrayList<String> redirects = new ArrayList<>();
 
     public RNFetchBlobReq(ReadableMap options, String taskId, String method, String url, ReadableMap headers, String body, ReadableArray arrayBody, final Callback callback) {
                 while (it.hasNextKey()) {
                     String key = it.nextKey();
                     String value = headers.getString(key);
-                    builder.header(key, value);
-                    mheaders.put(key,value);
+                    if(key.equalsIgnoreCase("RNFB-Response")) {
+                        if(value.equalsIgnoreCase("base64"))
+                            responseFormat = ResponseFormat.BASE64;
+                        else if (value.equalsIgnoreCase("utf8"))
+                            responseFormat = ResponseFormat.UTF8;
+                    }
+                    else {
+                        builder.header(key, value);
+                        mheaders.put(key, value);
+                    }
                 }
             }
 
                         // string correctly, we should do URL encoding before BASE64.
                         byte[] b = resp.body().bytes();
                         CharsetEncoder encoder = Charset.forName("UTF-8").newEncoder();
+                        if(responseFormat == ResponseFormat.BASE64) {
+                            callback.invoke(null, RNFetchBlobConst.RNFB_RESPONSE_BASE64, android.util.Base64.encodeToString(b, Base64.NO_WRAP));
+                            return;
+                        }
                         try {
                             encoder.encode(ByteBuffer.wrap(b).asCharBuffer());
                             // if the data contains invalid characters the following lines will be
                         // This usually mean the data is contains invalid unicode characters, it's
                         // binary data
                         catch(CharacterCodingException ignored) {
-                            callback.invoke(null, RNFetchBlobConst.RNFB_RESPONSE_BASE64, android.util.Base64.encodeToString(b, Base64.NO_WRAP));
+                            if(responseFormat == ResponseFormat.UTF8) {
+                                callback.invoke(null, RNFetchBlobConst.RNFB_RESPONSE_UTF8, "");
+                            }
+                            else {
+                                callback.invoke(null, RNFetchBlobConst.RNFB_RESPONSE_BASE64, android.util.Base64.encodeToString(b, Base64.NO_WRAP));
+                            }
                         }
                     }
                 } catch (IOException e) {

src/ios/RNFetchBlobNetwork.m

 NSMutableDictionary * progressTable;
 NSMutableDictionary * uploadProgressTable;
 
+typedef NS_ENUM(NSUInteger, ResponseFormat) {
+    UTF8,
+    BASE64,
+    AUTO
+};
+
 
 @interface RNFetchBlobNetwork ()
 {
     NSMutableDictionary * respInfo;
     NSInteger respStatus;
     NSMutableArray * redirects;
+    ResponseFormat responseFormat;
 }
 
 @end
     self.options = options;
     redirects = [[NSMutableArray alloc] init];
     [redirects addObject:req.URL.absoluteString];
+    
+    // set response format
+    NSString * rnfbResp = [req.allHTTPHeaderFields valueForKey:@"RNFB-Response"];
+    if([[rnfbResp lowercaseString] isEqualToString:@"base64"])
+        responseFormat = BASE64;
+    else if([[rnfbResp lowercaseString] isEqualToString:@"utf8"])
+        responseFormat = UTF8;
+    else
+        responseFormat = AUTO;
 
     NSString * path = [self.options valueForKey:CONFIG_FILE_PATH];
     NSString * ext = [self.options valueForKey:CONFIG_FILE_EXT];
             // if it turns out not to be `nil` that means the response data contains valid UTF8 string,
             // in order to properly encode the UTF8 string, use URL encoding before BASE64 encoding.
             NSString * utf8 = [[NSString alloc] initWithData:respData encoding:NSUTF8StringEncoding];
-
-            if(utf8 != nil)
+            
+            if(responseFormat == BASE64)
+            {
+                rnfbRespType = RESP_TYPE_BASE64;
+                respStr = [respData base64EncodedStringWithOptions:0];
+            }
+            else if (responseFormat == UTF8)
             {
                 rnfbRespType = RESP_TYPE_UTF8;
                 respStr = utf8;
             }
             else
             {
-                rnfbRespType = RESP_TYPE_BASE64;
-                respStr = [respData base64EncodedStringWithOptions:0];
+                if(utf8 != nil)
+                {
+                    rnfbRespType = RESP_TYPE_UTF8;
+                    respStr = utf8;
+                }
+                else
+                {
+                    rnfbRespType = RESP_TYPE_BASE64;
+                    respStr = [respData base64EncodedStringWithOptions:0];
+                }
             }
-
         }
     }