XX-net/XX-Net · warning

socks5 protocol error:%r

Error message

socks5 protocol error:%r

What it means

The X-Tunnel socks5_handler failed while reading the 4-byte SOCKS5 request header (read_bytes(4) threw). The exception is logged as a protocol error and the handler returns, dropping the connection. Typical cause: client disconnected after the greeting, or sent fewer bytes than required.

Source

Thrown at code/default/x_tunnel/local/proxy_handler.py:234

        reply = b"\x00\x5a" + addr_pack + struct.pack(">H", port)
        sock.send(reply)

        if len(self.read_buffer) - self.buffer_start:
            g.session.conn_list[conn_id].transfer_received_data(self.read_buffer[self.buffer_start:])

        g.session.conn_list[conn_id].start(block=True)

    def socks5_handler(self):
        sock = self.connection
        auth_mode_num = ord(self.read_bytes(1))
        data = self.read_bytes(auth_mode_num)

        sock.send(b"\x05\x00")  # socks version 5, no auth needed.
        try:
            data = self.read_bytes(4)
        except Exception as e:
            xlog.debug("socks5 auth num:%d, list:%s", auth_mode_num, utils.str2hex(data))
            xlog.warn("socks5 protocol error:%r", e)
            return

        socks_version = ord(data[0:1])
        if socks_version != 5:
            xlog.warn("request version:%d error", socks_version)
            return

        command = ord(data[1:2])
        if command != 1:  # 1. Tcp connect
            xlog.warn("request not supported command mode:%d", command)
            sock.send(b"\x05\x07\x00\x01")  # Command not supported
            return

        addrtype_pack = data[3:4]
        addrtype = ord(addrtype_pack)
        if addrtype == 1:  # IPv4
            addr_pack = self.read_bytes(4)
            addr = socket.inet_ntoa(addr_pack)

View on GitHub (pinned to cfa5bc17b6)

Solutions

  1. Usually benign; increase the read timeout if slow clients are being cut off
  2. Verify clients complete the full SOCKS5 handshake (version, command, addr-type, address)
  3. Ignore/log-filter if caused by scanners probing the port
Defensive patterns

Strategy: try-catch

Try / catch

try:
    data = self.read_bytes(4)
except Exception as e:
    xlog.warn('socks5 protocol error:%r', e)
    return

Prevention

When it happens

Trigger: Client sends SOCKS5 greeting, receives the no-auth reply, then closes or stalls before sending the 4-byte request — read_bytes times out or raises EOF.

Common situations: Probers that only complete half a handshake, real clients behind unstable connections, timeouts from read_bytes being shorter than slow clients need.

Related errors

AI-assisted analysis of XX-net/XX-Net@cfa5bc17b6 (2026-08-27). Data as JSON: /api/errors/c46e67dcd177134b. Report an issue: GitHub.