How to set content-type for request.response in Dart Server?

Question

I set my dart server as shown below. I can sent data from Flutter Mobile app and receive back from Dart Server.

If the request method is GET in dart Server I connect to tcp socket a get some data. the data I need to send to Flutter app must be in JSON format.

I try to set request.response.headers.contentType to json and I am keep getting an error that says HttpException: HTTP headers are not mutable.

Code Part:

var _secureResponse = {};
_secureResponse[“Data”] = "$_returningServerData";
_secureResult = json.encode(_secureResponse);

request.response.headers.contentType = new ContentType("application", "json", charset: "utf-8");
request.response.write(_secureResult);
request.response.close();

Error:

• null
• Unhandled exception: HttpException: HTTP headers are not mutable
• HttpHeaders._checkMutable (dart:_http/http_headers.dart:447:20)
• HttpHeaders.contentType= (dart:_http/http_headers.dart:267:5)

Server Code:

Future main() async {
  final HttpServer server = await HttpServer.bind("127.0.0.1", 8080);
  server.listen((HttpRequest request) async {

    print(request.headers.contentType);

    try {
      if (request.method == "GET") {
         String _requestData = ......
          Socket _socket = await Socket.connect('192.168.22.129', 3000);

          // READ FROM CSERVER
          _socket.listen((List<int> event) {
            _reply = new String.fromCharCodes(event).trim();
          });

          // WRITE TO SERVER
          _socket.add(utf8.encode('$_requestData\r\n'));

          // wait 1 seconds
          await Future.delayed(Duration(milliseconds: 1000));
          _socket.close();

          var _secureResponse = {};
          _secureResponse["Data"] = "$_reply";
          _secureResult = json.encode(_secureResponse);

          request.response.headers.contentType = new    
          ContentType("application", "json", charset: "utf-8");
          request.response.write(_secureResult);
          request.response.close();

        }

    } finally {
      var _secureResponse = {};
      _secureResponse["Data"] = "ERROR";
      _secureResult = json.encode(_secureResponse);

      request.response.headers.contentType = new 
      ContentType("application", "json", charset: "utf-8");
      request.response.write(_secureResult);
      request.response.close();
    }
  });
}

Answer 1

See https://api.dartlang.org/stable/2.1.0/dart-io/HttpHeaders-class.html

Did you try something like

request.headers.set(HttpHeaders.cacheControlHeader,
                    'max-age=3600, must-revalidate');

If you're building a server in Dart, may I suggest using package:shelf – it's much more user-friendly.