shadow1ng/fscan · error

%s: %w [socks5_handshake_write_failed]

Error message

%s: %w [socks5_handshake_write_failed]

What it means

Wrap of a conn.Write failure at the end of the SOCKS5 handshake: the server selected no-auth (response bytes 0x05 0x00) but could not send the method-selection reply to the client (broken/peer-reset connection). The i18n socks5_handshake_write_failed prefix marks the handshake write stage and %w preserves the underlying network error.

Source

Thrown at plugins/local/socks5proxy.go:183

		return fmt.Errorf("%s: %w", i18n.GetText("socks5_handshake_read_failed"), err)
	}

	if header[0] != 0x05 || header[1] == 0 {
		return fmt.Errorf("%s", i18n.GetText("socks5_unsupported_version"))
	}
	methods := make([]byte, int(header[1]))
	if _, err := io.ReadFull(conn, methods); err != nil {
		return fmt.Errorf("%s: %w", i18n.GetText("socks5_handshake_read_failed"), err)
	}
	if !containsByte(methods, 0x00) {
		_, _ = conn.Write([]byte{0x05, 0xff})
		return fmt.Errorf("%s", i18n.GetText("socks5_unsupported_version"))
	}

	// 发送握手响应（无认证）
	response := []byte{0x05, 0x00} // 版本5，无认证
	if _, err := conn.Write(response); err != nil {
		return fmt.Errorf("%s: %w", i18n.GetText("socks5_handshake_write_failed"), err)
	}

	return nil
}

// handleSocks5Request 处理SOCKS5连接请求
func (p *Socks5ProxyPlugin) handleSocks5Request(clientConn net.Conn, session *common.ScanSession) (net.Conn, int, error) {
	header := make([]byte, 4)
	if _, err := io.ReadFull(clientConn, header); err != nil {
		return nil, 0, fmt.Errorf("%s: %w", i18n.GetText("socks5_request_read_failed"), err)
	}

	if header[0] != 0x05 || header[2] != 0x00 {
		return nil, 0, fmt.Errorf("%s", i18n.GetText("socks5_invalid_request"))
	}

	cmd := header[1]
	if cmd != 0x01 { // 只支持CONNECT命令

View on GitHub (pinned to 95cc12e753)

Solutions

1. Drop the client connection; the proxy loop will accept new ones
2. Check for network instability or a client-side timeout
3. Ensure no firewall is resetting long-lived proxy connections

When it happens

Trigger: Thrown at plugins/local/socks5proxy.go:183 when the library encounters an invalid state.

Common situations: See trigger scenarios.

Understand the failure class

• SSL/TLS and certificate errors — how TLS handshakes and certificate validation fail.

AI-assisted analysis of shadow1ng/fscan@95cc12e753 (2026-09-06). Data as JSON: /api/errors/bbe7eea9e91aa413. Report an issue: GitHub.