2dust/v2rayN · error · ArgumentException

Invalid SOCKS5 UDP packet: IPv6 address incomplete

Error message

Invalid SOCKS5 UDP packet: IPv6 address incomplete

What it means

Thrown when ATYP indicates IPv6 (0x04) but fewer than 16 bytes remain for the 128-bit address. Same truncation guard as the IPv4 case but sized for 16 octets.

Source

Thrown at v2rayN/ServiceLib.UdpTest/Socks5UdpChannel.cs:144

        switch (addressType)
        {
            case Socks5AddressData.AddrTypeIPv4:
                if (packet.Length < offset + 4)
                {
                    throw new ArgumentException("Invalid SOCKS5 UDP packet: IPv4 address incomplete");
                }

                var ipv4Bytes = new byte[4];
                Array.Copy(packet, offset, ipv4Bytes, 0, 4);
                host = new IPAddress(ipv4Bytes).ToString();
                addressLength = 4;
                isDomain = false;
                break;

            case Socks5AddressData.AddrTypeIPv6:
                if (packet.Length < offset + 16)
                {
                    throw new ArgumentException("Invalid SOCKS5 UDP packet: IPv6 address incomplete");
                }

                var ipv6Bytes = new byte[16];
                Array.Copy(packet, offset, ipv6Bytes, 0, 16);
                host = new IPAddress(ipv6Bytes).ToString();
                addressLength = 16;
                isDomain = false;
                break;

            case Socks5AddressData.AddrTypeDomain:
                if (packet.Length < offset + 1)
                {
                    throw new ArgumentException("Invalid SOCKS5 UDP packet: domain length missing");
                }

                var domainLength = packet[offset++];
                if (packet.Length < offset + domainLength)
                {

View on GitHub (pinned to e01717d832)

Solutions

Catch ArgumentException per attempt and continue (the response is unusable but the test loop can retry).
Confirm the proxy encodes IPv6 with ATYP 0x04 + 16 address bytes + 2 port bytes per RFC 1928.
If the target resolves to IPv6, prefer a dual-stack proxy and ensure the relay path supports 16-byte address headers.
Log ATYP and remaining-length at failure to confirm truncation vs. proxy bug.

Defensive patterns

Strategy: try-catch

Validate before calling

// Pre-check IPv6 address availability
static bool HasFullIPv6(byte[] p, int offset) => p != null && p.Length >= offset + 16;

Type guard

static bool IsCompleteIPv6Packet(byte[] packet, int offset) => packet != null && offset + 16 + 2 <= packet.Length;

Try / catch

try
{
    var (remote, data) = ParseSocks5UdpPacket(packet);
}
catch (ArgumentException ex) when (ex.Message.Contains("IPv6 address incomplete"))
{
    // truncated IPv6 relay packet; retry or mark attempt failed
}

Prevention

Catch the ArgumentException per attempt rather than letting it propagate.
Verify the proxy writes 16-byte IPv6 addresses with ATYP 0x04.
Ensure the relay path supports the larger IPv6-headed packet without truncation.

When it happens

Trigger: ParseSocks5UdpPacket reads ATYP == AddrTypeIPv6 then packet.Length < offset + 16; the datagram was cut short inside the IPv6 address field.

Common situations: Truncated IPv6 relay response; proxy reporting an IPv6 ATYP without a full 16-byte address; MTU/fragmentation truncating an already-large IPv6-headed packet.

Related errors

AI-assisted analysis of 2dust/v2rayN@e01717d832 (2026-08-13). Data as JSON: /api/errors/f3a38b10e573fad9. Report an issue: GitHub.