How to set up charset (encoding) in HttpConnection

I try to connect to web in script from Illustrator. How to set up charset (encoding) in HttpConnection?

This code does not working:

var script = '';
script += 'if ( !ExternalObject.webaccesslib )\n';
script +=
    '  ExternalObject.webaccesslib = new ExternalObject(\'lib:webaccesslib\');\n';
script += 'var response = null;\n';
script += 'var retry = true;\n';
script += 'while (retry) {\n';
script += '  var http = new HttpConnection(\'' + url + '\') ; \n';
script += '  http.mime = "application/x-www-form-urlencoded; charset=UTF-8"; \n';
script += '  http.requestheaders = ["charset", "UTF-8"];\n';
script += '  http.timeout  = ' + httpTimeout + ';\n';
script += '  http.execute() ;\n';
script += '  try{\n';
script += '    response = http.response;\n';
script += '    retry = false;\n';
script += '  } catch (e){\n';
script += '    BridgeTalk.bringToFront(\'bridge\');\n';
script +=
    '    if (!confirm(\'There was an error communicating with the server. Would you like to retry?\'))\n';
script += '      retry = false;\n';
script += '  }\n';
script += '}\n';
script += 'response;\n';