Error: "connection already exists" in AddConn Method of 'connMultiplexer'

[minchopm]

Description:

I encountered a panic error stating "connection already exists" while using webtransport-go. The error occurs in the AddConn method of the connMultiplexer struct within the quic-go package. Below is a detailed explanation of the problem along with the relevant code snippets.

Code Implementation:
Server:

func ServerWT(conn net.PacketConn) {
	tlsConfig, _ := generateTLSConfig3("<server addr>")
	s := webtransport.Server{
		H3: http3.Server{
			Addr:      ":9000",
			TLSConfig: tlsConfig,
			QUICConfig: &quic.Config{
				EnableDatagrams:       true,
				MaxIdleTimeout:        60 * time.Second,
				KeepAlivePeriod:       15 * time.Second,
				MaxIncomingStreams:    1000,
				MaxIncomingUniStreams: 1000,
			},
		},
		ReorderingTimeout: time.Duration(100 * time.Second),
	}

	http.HandleFunc("/webtransport", func(w http.ResponseWriter, r *http.Request) {

		fmt.Println("Connection:", r)
		_, err := s.Upgrade(w, r)
		if err != nil {
			fmt.Println("Upgrading failed: ", err)
			w.WriteHeader(500)
			return
		}

	})
	fmt.Println("WT server serving")
	err := s.Serve(conn)
	if err != nil {
		fmt.Println("Failed to start server:", err)
	}
}

Client:

func WtClient(udpClient net.PacketConn, addr string) {
	go SendDataClientWT()
	blockUpgrade := make(chan struct{})
	d := webtransport.Dialer{
		TLSClientConfig: &tls.Config{
			InsecureSkipVerify: true,
		},
		QUICConfig: &quic.Config{
			EnableDatagrams:       true,
			MaxIdleTimeout:        60 * time.Second,
			KeepAlivePeriod:       15 * time.Second,
			MaxIncomingStreams:    1000,
			MaxIncomingUniStreams: 1000,
		},
		DialAddr: func(ctx context.Context, addr string, tlsConf *tls.Config, conf *quic.Config) (quic.EarlyConnection, error) {
			udpAddr, err := net.ResolveUDPAddr("udp4", addr)
			if err != nil {
				fmt.Println("ResolveUDPAddr error:", err)
				return nil, err
			}
			conn, err := quic.DialEarly(ctx, udpClient, udpAddr, tlsConf, conf)
			if err != nil {
				fmt.Println("DialEarly err: ", err)
				return nil, err
			}
			return &requestStreamDelayingConn{done: blockUpgrade, EarlyConnection: conn}, nil
		},
	}

	headers := http.Header{}
	rsp, conn, err := d.Dial(context.Background(), "https://"+addr+"/webtransport", headers)
	if err != nil {
		fmt.Println("Dial err: ", err)
		return
	}
	sessionWT = conn
	go StartAudioRecording()
	fmt.Println("Connection established: ", conn)
	fmt.Println("Response: ", rsp)
	fmt.Println("Enter messages to send, type 'exit' to quit:")
}

main:

func main() {
	addr := net.UDPAddr{
		Port: 3344,
		IP:   net.ParseIP("0.0.0.0"),
	}
	conn, _ := net.ListenUDP("udp", &addr)
	// Set UDP socket options
	go ServerWT(conn)
	WtClient(conn, "localhost:3344")
}

Error:

panic: connection already exists

goroutine 3 [running]:
github.com/quic-go/quic-go.(*connMultiplexer).AddConn(0x140000a61a0, {0x1038da998?, 0x1400005a040?})
        ../go/pkg/mod/github.com/quic-go/quic-go@v0.45.0/multiplexer.go:59 +0x198
...

Problematic Code:

func (m *connMultiplexer) AddConn(c indexableConn) {
    m.mutex.Lock()
    defer m.mutex.Unlock()

    connIndex := m.index(c.LocalAddr())
    p, ok := m.conns[connIndex]
    if ok {
        panic("connection already exists")
    }
    m.conns[connIndex] = p
}

Details:

I am attempting to establish a WebTransport server and client using the webtransport-go library.
The server initializes and listens for connections using the QUIC protocol.
Upon establishing a connection, the server attempts to add the connection to the multiplexer, resulting in a panic indicating that the connection already exists.
Steps to Reproduce:

Run the provided code.
Observe the panic error with the message "connection already exists".
Expected Behavior:
The server should establish connections without encountering a panic, handling multiple connections appropriately.

Request:

Please provide guidance on resolving this issue.
If this is a known issue, suggest any workarounds or fixes.
Update the documentation if necessary to reflect any changes or known limitations.
Thank you for your assistance.

[marten-seemann]

I will not be able to investigate this. Please see the README for details on the funding situation of the project.