shadow1ng/fscan · error

invalid output format: %s

Error message

invalid output format: %s

What it means

Default-branch guard in InitOutput's format switch: fv.OutputFormat is not one of "txt", "json", or "csv", so no output.Format can be selected for the requested output file. The invalid format string is echoed so the user can correct the flag.

Source

Thrown at common/output_api.go:51

	}

	outputFile := fv.Outputfile
	outputFormat := fv.OutputFormat

	if outputFile == "" {
		return fmt.Errorf("output file not specified")
	}

	var format output.Format
	switch outputFormat {
	case "txt":
		format = output.FormatTXT
	case "json":
		format = output.FormatJSON
	case "csv":
		format = output.FormatCSV
	default:
		return fmt.Errorf("invalid output format: %s", outputFormat)
	}

	// 如果使用默认文件名但格式不是txt，自动修正扩展名
	if outputFile == "result.txt" && outputFormat != "txt" {
		outputFile = "result." + outputFormat
	}

	config := output.DefaultManagerConfig(outputFile, format)
	manager, err := output.NewManager(config)
	if err != nil {
		return err
	}
	ResultOutput = manager
	return nil
}

// CloseOutput 关闭输出系统
func CloseOutput() error {

View on GitHub (pinned to 95cc12e753)

Solutions

1. Use one of: txt, json, csv (lowercase)
2. Normalize the format with strings.ToLower before InitOutput
3. Add autocomplete/validation in the CLI layer

Example fix

// before
fv.OutputFormat = "JSON"
// after
fv.OutputFormat = strings.ToLower("JSON") // "json"

switch strings.ToLower(fv.OutputFormat) {
case "txt", "json", "csv":
default:
    return fmt.Errorf("format must be txt|json|csv, got %q", fv.OutputFormat)
}

func validFormat(s string) bool {
    switch strings.ToLower(s) { case "txt", "json", "csv": return true }
    return false
}

if err := InitOutput(fv); err != nil {
    if strings.Contains(err.Error(), "invalid output format") { log.Fatalf("%v", err) }
}

When it happens

Trigger: Setting fv.OutputFormat to something like 'xml', 'JSON' (uppercase), 'yaml', or an empty string that survives default handling.

Common situations: Typo in config file; uppercase/lowercase mismatch; copying a format name from another tool; defaulting logic failed to set a format.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• output file not specified
• result cannot be nil
• result cannot be nil
• parser_cidr_failed: %w
• parser_ip_range_failed: %w

AI-assisted analysis of shadow1ng/fscan@95cc12e753 (2026-09-06). Data as JSON: /api/errors/da1f0ebac07aad88. Report an issue: GitHub.