http - In Dart on server-side, how to set headers in HttpClient -

i trying use dart httpclient class (io library / server-side!) , can not think how equivalent of dart (client-side) call setrequestheader.

specifically want set "content-type" "application/json"

as per line (from client-side):

request.setrequestheader("content-type", "application/json");

i'm using format:

new httpclient().posturl(uri.parse(url))              .then((httpclientrequest  request)  => request.close())        .then((httpclientresponse response) => response.transform(new utf8decoder()).listen(_set_dbstats)); 

and when try insert:

.then((httpclientrequest  request) => request.head("content-type", "application/json")) 

i'm informed (in dart editor) head not method request... (although see in api?!) related being used post?

thanks in advance!

here snippet of working code evolved numerous tests , dealing issues outside scope of original question.

guenter zoechbauer heroically worked me off-line dones, not find examples of 1. server side, 2. post 3. http commands using headers, format permits this...

import 'package:http/http.dart' http;  string url = "https://whatever.com"; return new http.client()    .post(url, headers: {'content-type': 'application/json'},     body: '{"distinct": "users","key": "account","query": {"active":true}}')    .whencomplete(() => print('completed'))    .then((http.response r) => r.body); }