Prevent multiple close of channel

emlid/reachview/broadcast.go

@@ -2,6 +2,7 @@ package reachview
 
 import (
 	"context"
+	"sync"
 
 	gosocketio "forge.cadoles.com/Pyxis/golang-socketio"
 	"github.com/mitchellh/mapstructure"
@@ -31,6 +32,8 @@ type Broadcast struct {
 func (c *Client) Broadcast(ctx context.Context) (chan Broadcast, error) {
 	out := make(chan Broadcast)
 
+	closer := new(sync.Once)
+
 	handler := func(_ *gosocketio.Channel, data interface{}) {
 		res := Broadcast{}
 		if err := mapstructure.WeakDecode(data, &res); err != nil {
@@ -38,8 +41,12 @@ func (c *Client) Broadcast(ctx context.Context) (chan Broadcast, error) {
 		}
 		select {
 		case <-ctx.Done():
-			c.Off(eventBroadcast)
-			close(out)
+			closer.Do(func() {
+				c.Off(eventBroadcast)
+				close(out)
+			})
+
+			return
 		default:
 			out <- res
 		}