dart server listen how to recive json data

import 'dart:io';import 'dart:convert';String _host = InternetAddress.loopbackIPv4.host;Future main() async {  var server = await HttpServer.bind(_host, 4049);  await for (var req in server) {    ContentType contentType = req.headers.contentType;    HttpResponse response = req.response;    if (req.method == 'POST' &&        contentType?.mimeType == 'application/json' /*1*/) {      try {        String content =            await utf8.decoder.bind(req).join(); /*2*/        var data = jsonDecode(content) as Map; /*3*/        var fileName = req.uri.pathSegments.last; /*4*/        await File(fileName)            .writeAsString(content, mode: FileMode.write);        req.response          ..statusCode = HttpStatus.ok          ..write('Wrote data for ${data['name']}.');      } catch (e) {        response          ..statusCode = HttpStatus.internalServerError          ..write('Exception during file I/O: $e.');      }    } else {      response        ..statusCode = HttpStatus.methodNotAllowed        ..write('Unsupported request: ${req.method}.');    }    await response.close();  }}