Function SafeFilename

context/context.go:2401–2440

SafeFilename returns a safe filename based on the given name. - Using filepath.Base and filepath.ToSlash: This ensures that only the base file name is used, without any directory components, and converts all separators to slashes. This is a good practice to prevent directory traversal. - Regular Exp

(prefixDir string, name string)

//
// It returns the safe prefix directory (destination directory), the safe filename, a boolean indicating whether the filename is safe, and an error if any.
func SafeFilename(prefixDir string, name string) (string, string, bool, error) {
	// Security fix for go < 1.17.5:
	// Reported by Kirill Efimov (snyk.io) through security reports.
	filename := filepath.Base(filepath.ToSlash(name))

	// CWE-99.

	// Sanitize the user input by using a regular expression
	// and an allowlist of valid extensions
	isValidFilename := ValidFilenameRegexp.MatchString(filename)
	if !isValidFilename {
		// Reject the input as it is invalid or unsafe.
		return prefixDir, name, false, nil
	}

	if ValidExtensionRegexp != nil && !ValidExtensionRegexp.MatchString(filename) {
		// Reject the input as it is invalid or unsafe.
		return prefixDir, name, false, nil
	}

	var destPath string
	if prefixDir != "" {
		// Join the sanitized input with the destination directory.
		destPath = filepath.Join(prefixDir, filename)

		// Get the canonical path of the destination directory.
		canonicalDestDir, err := filepath.EvalSymlinks(prefixDir) // the prefix dir should exists.
		if err != nil {
			return prefixDir, name, false, fmt.Errorf("dest directory: %s: eval symlinks: %w", prefixDir, err)
		}

		// Check if the destination path is within the destination directory.
		if !strings.HasPrefix(destPath, canonicalDestDir) {
			// Reject the input as it is a path traversal attempt.
			return prefixDir, name, false, nil
		}
	}

	return destPath, filename, true, nil
}

// UploadFormFiles uploads any received file(s) from the client
// to the system physical location "destDirectory".