egametang/ET · critical · Exception

bind error: {ipEndPoint}

Error message

bind error: {ipEndPoint}

What it means

IKcpTransport constructor binds a UDP socket to ipEndPoint and wraps any Bind failure. UDP bind can fail for the same reasons TCP can: port in use, address not assigned to a host, or insufficient privileges for low ports.

Source

Thrown at Packages/cn.etetet.core/Scripts/Core/Share/Network/IKcpTransport.cs:45

            NetworkHelper.SetSioUdpConnReset(this.socket);
        }
        
        public UdpTransport(IPEndPoint ipEndPoint)
        {
            this.socket = new Socket(ipEndPoint.AddressFamily, SocketType.Dgram, ProtocolType.Udp);
            if (!RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
            {
                this.socket.SendBufferSize = Kcp.OneM * 64;
                this.socket.ReceiveBufferSize = Kcp.OneM * 64;
            }
            
            try
            {
                this.socket.Bind(ipEndPoint);
            }
            catch (Exception e)
            {
                throw new Exception($"bind error: {ipEndPoint}", e);
            }

            NetworkHelper.SetSioUdpConnReset(this.socket);
        }
        
        public void Send(byte[] bytes, int index, int length, EndPoint endPoint, ChannelType channelType)
        {
            this.socket.SendTo(bytes, index, length, SocketFlags.None, endPoint);
        }
        
        public int Recv(byte[] buffer, ref EndPoint endPoint)
        {
            return this.socket.ReceiveFrom(buffer, ref endPoint);
        }

        public IPEndPoint GetBindPoint()
        {
            return this.socket.LocalEndPoint as IPEndPoint;

View on GitHub (pinned to 5cab01f7a8)

Solutions

1. Free the port: stop the other process or let the OS release it (SO_REUSEADDR if your OS path allows).
2. Bind to a local IP that exists (use IPAddress.Any or a confirmed interface address).
3. Use an unprivileged port (>=1024) or run with elevated privileges.
4. Read the wrapped inner SocketException for the exact socket error code.

Example fix

// before
this.socket.Bind(ipEndPoint);
// after
var local = ipEndPoint.Address.Equals(IPAddress.Any) ? ipEndPoint : ipEndPoint;
this.socket.Bind(local); // ensure local.Address is assigned to this host

static bool IsPortFreeUDP(IPEndPoint ep)
{
    try { using var s = new Socket(ep.AddressFamily, SocketType.Dgram, ProtocolType.Udp); s.Bind(ep); return true; }
    catch { return false; }
}

null

try { transport = new KcpTransport(ipEndPoint); }
catch (Exception e) when (e.Message.StartsWith("bind error"))
{ Log.Error($"udp bind failed for {ipEndPoint}: {e.InnerException?.Message}"); throw; }

When it happens

Trigger: Two services binding the same UDP port, binding to an IP not present on the machine, or binding a port <1024 as non-root on Linux.

Common situations: Process restarted while the old socket is still in TIME_WAIT / held, misconfigured outer IP, or another instance already running.

Related errors

• kchannel connected but kcp is zero!
• GetChannelConn conn not found KChannel! {channelId}
• socket set buffer error: {this.sendBuffer.First.Length}, {th
• bind error: {ipEndPoint}
• socket error: {e.LastOperation}

AI-assisted analysis of egametang/ET@5cab01f7a8 (2026-08-13). Data as JSON: /api/errors/629b09ca25724fc7. Report an issue: GitHub.