net::ERR_EMPTY_RESPONSE when establish websocket connection

Question

I run a websocket server on machine and connect to websocket server like this:

var websocket = new WebSocket("ws://127.0.0.1:8989");
websocket.onopen = function (event) {
  console.log("onopen");
};
websocket.onerror = function (error) {
  console.log("onerror: " + event.data);
};
websocket.onmessage = function (message) {
  console.log("onmessage: " + message.data);
};
websocket.onclose = function(closeEvent) {
  console.log("WebSocket Server quit");
}

On this condition, it did work. I get an error net::ERR_EMPTY_RESPONSE when connect to server if set http_proxy, but it could work after change connect ip address which get by ifconfig command like this:

   var websocket = new WebSocket("ws://192.168.28.160:8989");

Can anyone give me an explanation ？