Fixes unregistering a channel on a possibly closed stream data broadc…

…aster

agents/http3_agent.go

@@ -251,7 +251,11 @@ func (a *HTTP3Agent) SendRequest(path, method, authority string, headers map[str
 	a.responseBuffer[streamID] = response
 
 	go func() { // Pipes the data from the response stream to the agent
-		defer stream.ReadChan.Unregister(streamChan)
+		defer func() {
+			if !stream.ReadChan.IsClosed() {
+				stream.ReadChan.Unregister(streamChan)
+			}
+		}()
 		for {
 			select {
 			case i := <-streamChan:

utils.go

@@ -5,6 +5,7 @@ import "github.com/dustin/go-broadcast"
 type Broadcaster struct {
 	broadcast.Broadcaster
 	channels []chan interface{}
+	isClosed bool
 }
 
 func NewBroadcaster(buflen int) Broadcaster {
@@ -19,8 +20,15 @@ func (b *Broadcaster) RegisterNewChan(size int) chan interface{} {
 }
 
 func (b *Broadcaster) Close() error {
+	if b.isClosed {
+		return nil
+	}
+	b.isClosed = true
 	for _, c := range b.channels {
 		close(c)
 	}
 	return b.Broadcaster.Close()
+}
+func (b *Broadcaster) IsClosed() bool {
+	return b.isClosed
 }