sentry: support save / restore of TCP bind socket after shutdown.

PiperOrigin-RevId: 224227677
Change-Id: I08b0e0c0574170556269900653e5bcf9e9e5c9c9

pkg/tcpip/transport/tcp/endpoint_state.go

@@ -92,8 +92,8 @@ func (e *endpoint) beforeSave() {
 		panic("endpoint still has waiters upon save")
 	}
 
-	if !((e.state == stateBound || e.state == stateListen) == e.isPortReserved) {
-		panic("endpoint port must and must only be reserved in bound or listen state")
+	if e.state != stateClosed && !((e.state == stateBound || e.state == stateListen) == e.isPortReserved) {
+		panic("endpoints which are not in the closed state must have a reserved port IFF they are in bound or listen state")
 	}
 }
 
@@ -102,15 +102,21 @@ func (e *endpoint) saveAcceptedChan() []*endpoint {
 	if e.acceptedChan == nil {
 		return nil
 	}
-	close(e.acceptedChan)
 	acceptedEndpoints := make([]*endpoint, len(e.acceptedChan), cap(e.acceptedChan))
-	i := 0
-	for ep := range e.acceptedChan {
-		acceptedEndpoints[i] = ep
-		i++
+	for i := 0; i < len(acceptedEndpoints); i++ {
+		select {
+		case ep := <-e.acceptedChan:
+			acceptedEndpoints[i] = ep
+		default:
+			panic("endpoint acceptedChan buffer got consumed by background context")
+		}
 	}
-	if i != len(acceptedEndpoints) {
-		panic("endpoint acceptedChan buffer got consumed by background context")
+	for i := 0; i < len(acceptedEndpoints); i++ {
+		select {
+		case e.acceptedChan <- acceptedEndpoints[i]:
+		default:
+			panic("endpoint acceptedChan buffer got populated by background context")
+		}
 	}
 	return acceptedEndpoints
 }
@@ -235,7 +241,20 @@ func (e *endpoint) afterLoad() {
 			bind()
 			tcpip.AsyncLoading.Done()
 		}()
-	case stateClosed, stateError:
+	case stateClosed:
+		if e.isPortReserved {
+			tcpip.AsyncLoading.Add(1)
+			go func() {
+				connectedLoading.Wait()
+				listenLoading.Wait()
+				connectingLoading.Wait()
+				bind()
+				e.state = stateClosed
+				tcpip.AsyncLoading.Done()
+			}()
+		}
+		fallthrough
+	case stateError:
 		tcpip.DeleteDanglingEndpoint(e)
 	}
 }