2dust/v2rayN · error · ArgumentException

Invalid SOCKS5 UDP packet: port incomplete

Error message

Invalid SOCKS5 UDP packet: port incomplete

What it means

Thrown when fewer than 2 bytes remain after the address for the big-endian port field. The parser needs exactly 2 bytes for the port; a short datagram here means the relay packet was truncated at the very end.

Source

Thrown at v2rayN/ServiceLib.UdpTest/Socks5UdpChannel.cs:180

                {
                    throw new ArgumentException("Invalid SOCKS5 UDP packet: domain incomplete");
                }

                host = Encoding.ASCII.GetString(packet, offset, domainLength);
                addressLength = domainLength;
                isDomain = true;
                break;

            default:
                throw new NotSupportedException($"Unsupported SOCKS5 address type: {addressType}");
        }

        offset += addressLength;

        // Port (2 bytes, big-endian)
        if (packet.Length < offset + 2)
        {
            throw new ArgumentException("Invalid SOCKS5 UDP packet: port incomplete");
        }

        var port = BinaryPrimitives.ReadUInt16BigEndian(packet.AsSpan(offset, 2));
        offset += 2;

        // Data (remaining bytes)
        var dataLength = packet.Length - offset;
        var data = new byte[dataLength];
        if (dataLength > 0)
        {
            Array.Copy(packet, offset, data, 0, dataLength);
        }

        // Create remote endpoint without DNS resolution
        var remote = new Socks5RemoteEndpoint(host, port, isDomain);
        return (remote, data);
    }

View on GitHub (pinned to e01717d832)

Solutions

  1. Catch ArgumentException per attempt and continue.
  2. Confirm the proxy always appends a 2-byte big-endian port after the address per RFC 1928.
  3. Re-validate the address-length math (especially for domain type) to ensure offset is correct before the port read.
  4. Log offset and total length at failure to locate the truncation.
Defensive patterns

Strategy: try-catch

Validate before calling

// Pre-check port field availability
static bool HasPortBytes(byte[] p, int offset) => p != null && p.Length >= offset + 2;

Type guard

static bool HasCompletePort(byte[] packet, int offset) => packet != null && offset + 2 <= packet.Length;

Try / catch

try
{
    var (remote, data) = ParseSocks5UdpPacket(packet);
}
catch (ArgumentException ex) when (ex.Message.Contains("port incomplete"))
{
    // truncated at the port field; mark attempt failed
}

Prevention

When it happens

Trigger: ParseSocks5UdpPacket has consumed RSV/FRAG/ATYP/address, then packet.Length < offset + 2 before reading the port.

Common situations: Datagram truncated just before the port field; proxy that omits the 2-byte port; earlier address-length misparse leaving the offset wrong so the port read overruns the buffer.

Related errors

AI-assisted analysis of 2dust/v2rayN@e01717d832 (2026-08-13). Data as JSON: /api/errors/dd8d9aca72918ed4. Report an issue: GitHub.