shadow1ng/fscan · error

domain_format_invalid

Error message

domain_format_invalid

What it means

Generic guard in the domain (address type 0x03) branch: io.ReadFull failed while reading the 1-byte domain length prefix. It fires when the connection ends or times out before the client sends the domain-name length byte, i.e. a truncated domain request rather than a syntactically bad domain.

Source

Thrown at plugins/local/socks5proxy.go:224

	}

	// 解析目标地址
	addrType := header[3]
	var targetHost string
	var targetPort int

	switch addrType {
	case 0x01: // IPv4
		addr := make([]byte, 6)
		if _, err := io.ReadFull(clientConn, addr); err != nil {
			return nil, 0, fmt.Errorf("%s", i18n.GetText("ipv4_address_invalid"))
		}
		targetHost = fmt.Sprintf("%d.%d.%d.%d", addr[0], addr[1], addr[2], addr[3])
		targetPort = int(addr[4])<<8 + int(addr[5])
	case 0x03: // 域名
		lenBuf := make([]byte, 1)
		if _, err := io.ReadFull(clientConn, lenBuf); err != nil {
			return nil, 0, fmt.Errorf("%s", i18n.GetText("domain_format_invalid"))
		}
		domainLen := int(lenBuf[0])
		if domainLen == 0 {
			return nil, 0, fmt.Errorf("%s", i18n.GetText("domain_length_invalid"))
		}
		addr := make([]byte, domainLen+2)
		if _, err := io.ReadFull(clientConn, addr); err != nil {
			return nil, 0, fmt.Errorf("%s", i18n.GetText("domain_length_invalid"))
		}
		targetHost = string(addr[:domainLen])
		targetPort = int(addr[domainLen])<<8 + int(addr[domainLen+1])
	case 0x04: // IPv6
		addr := make([]byte, 18)
		if _, err := io.ReadFull(clientConn, addr); err != nil {
			return nil, 0, fmt.Errorf("%s", i18n.GetText("ipv6_address_invalid"))
		}
		// IPv6地址解析（简化实现）
		targetHost = net.IP(addr[:16]).String()

View on GitHub (pinned to 95cc12e753)

Solutions

1. Verify the client sends the complete domain request (length byte, domain bytes, 2 port bytes)
2. Check for intermediate middleboxes or timeouts cutting the connection
3. Set an explicit read deadline so partial reads fail deterministically

When it happens

Trigger: Thrown at plugins/local/socks5proxy.go:224 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of shadow1ng/fscan@95cc12e753 (2026-09-06). Data as JSON: /api/errors/1954f99d1636a76d. Report an issue: GitHub.