shadow1ng/fscan · error

%s: %w [socks5_request_read_failed]

Error message

%s: %w [socks5_request_read_failed]

What it means

Wrap of an io.ReadFull failure at the start of handleSocks5Request: the 4-byte SOCKS5 request header (VER, CMD, RSV, ATYP) could not be read from the client connection, typically a mid-session disconnect or timeout after a successful handshake. The i18n socks5_request_read_failed prefix identifies the request-read stage and %w preserves the I/O cause.

Source

Thrown at plugins/local/socks5proxy.go:193

	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
		// 发送不支持的命令响应
		response := []byte{0x05, 0x07, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}
		_, _ = clientConn.Write(response)
		return nil, 0, fmt.Errorf(i18n.GetText("socks5_unsupported_command")+": %d", cmd)
	}

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

View on GitHub (pinned to 95cc12e753)

Solutions

1. Verify the client actually speaks SOCKS5 and stays connected for the full request phase (header read happens right after the handshake reply)
2. Check for network intermediaries (LB idle timeouts, NAT, firewalls) dropping long-lived proxied connections and tighten keepalives
3. If reading times out repeatedly, inspect the client's read deadlines set around the proxy connection and raise forward.Timeout
4. Capture the returned error with errors.Unwrap to distinguish EOF/timeout from a protocol-level refusal and handle client disconnects as non-fatal

When it happens

Trigger: Thrown at plugins/local/socks5proxy.go:193 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/d4c60c5b10030388. Report an issue: GitHub.