http - Is there a way to be notified when a client has unsubscribe from server sent events? -

as understand when request event emitter on server arrives, request never closed , need res.write() every time send message. there way notified when client performed request has left? there property on request object?

suppose have following route

app.get('/event',function(req,res){  //set response headers  //how check if req object still active send message , perform other actions?  }) 

the basic sequence of events should similar in other frameworks, example grails 3.3.

first set endpoints subscribe, , close connection.

def index() {     // handler /api/subscribe      rx.stream { observer observer ->          // grails event bus. background tasks,         // services , other controllers can post these         // events, client_hangup, send_msg,         // string constants.          eventbus.subscribe(client_hangup) {string msg ->              // code handle when grails event bus             // posts client_hangup             // side effects here, update counter             // close sse connection              observer.oncompleted()             return         }          eventbus.subscribe(send_msg) {string msg ->              // send server sent event              observer.onnext(rx.respond(msg))         }     } }    def disconnecting() {     // handler /api/disconnect     // post client_hangup event grails event bus      notify(client_hangup, 'disconnect') } 

now in client, need arrange get /api/disconnect whenever use-case requires it. assuming want notice when navigates away page, register function on window.onbeforeunload. example using vue.js , axios.

  window.onbeforeunload = function (e) {     e.preventdefault()     vue.$http({       method: 'get',       url: 'http://localhost:8080/api/disconnect'     })       .then((response) => { console.log(response) })       .catch(({error}) => { console.log(error) })   } 

in case of servlet stacks grails, found needed if had no housekeeping of own when browser went away. without it, page reloads causing ioexceptions on end.