add connection monitor to sources

client/lib/source/poll-source.ts

@@ -1,4 +1,4 @@
-import { BehaviorSubject, concat, from, Observable, of } from 'rxjs'
+import { BehaviorSubject, concat, from, Observable, of, Subject } from 'rxjs'
 import { concatMap, delay, skip, switchMap, take, tap } from 'rxjs/operators'
 import { Store } from '../store'
 import { Http, Update } from '../types'
@@ -9,6 +9,7 @@ export type PollConfig = {
 }
 
 export class PollSource<T> implements Source<T> {
+  connectionMade$ = new Subject<void>()
 
   constructor (
     private readonly pollConfig: PollConfig,
@@ -34,14 +35,15 @@ export class PollSource<T> implements Source<T> {
     const poll$ = concat(updates$, delay$)
 
     return polling$.pipe(
-       switchMap(_ => poll$),
-       concatMap(res => {
+      switchMap(_ => poll$),
+      concatMap(res => {
+        this.connectionMade$.next()
         if (Array.isArray(res)) {
           return from(res) // takes Revision[] and converts it into Observable<Revision>
         } else {
           return of(res) // takes Dump<T> and converts it into Observable<Dump<T>>
         }
-       }),
+      }),
     )
   }
 }