clarify: make a case for each banned rune

stringutils/stringutils.go

@@ -3,24 +3,119 @@ package stringutils
 // ContainsDisallowedRune checks whether the given input contains a disallowed rune
 func ContainsDisallowedRune(input string) bool {
 	for _, r := range input {
-		switch {
-		case 0 <= r && r <= 8:
+		if isTerminalControlCharacter(r) {
 			return true
-		case r == '\t': // 9
-			continue
-		case 11 <= r && r <= 12:
-			return true
-		case r == '\n': // 10
-			continue
-		case r == '\r': // 13
-			continue
-		case 14 <= r && r <= 31:
-			return true
-		case r == 127: // DEL
-			return true
-		default:
-			continue
+
 		}
 	}
 	return false
 }
+
+func isTerminalControlCharacter(r rune) bool {
+
+	switch r {
+	default:
+		// any character not in this list is not a terminal control character
+		return false
+
+	case 0: // NUL Null char
+		return true
+
+	case 1: // SOH Start of Heading
+		return true
+
+	case 2: // STX Start of Text
+		return true
+
+	case 3: // ETX End of Text
+		return true
+
+	case 4: // EOT End of Transmission
+		return true
+
+	case 5: // ENQ Enquiry
+		return true
+
+	case 6: // ACK Acknowledgment
+		return true
+
+	case 7: // BEL Bell
+		return true
+
+	case 8: // BS  Back Space
+		return true
+
+		// 9: HT  Horizontal Tab
+
+		// 10: LF Line Feed
+
+	case 11: // VT  Vertical Tab
+		return true
+
+	case 12: // FF  Form Feed
+		return true
+
+		// 13: Carriage Return
+
+	case 14: // SO  Shift Out / X-On
+		return true
+
+	case 15: // SI  Shift In / X-Off
+		return true
+
+	case 16: // DLE Data Line Escape
+		return true
+
+	case 17: // DC1 Device Control 1 (oft. XON)
+		return true
+
+	case 18: // DC2 Device Control 2
+		return true
+
+	case 19: // DC3 Device Control 3 (oft. XOFF)
+		return true
+
+	case 20: // DC4 Device Control 4
+		return true
+
+	case 21: // NAK Negative Acknowledgement
+		return true
+
+	case 22: // SYN Synchronous Idle
+		return true
+
+	case 23: // ETB End of Transmit Block
+		return true
+
+	case 24: // CAN Cancel
+		return true
+
+	case 25: // EM  End of Medium
+		return true
+
+	case 26: // SUB Substitute
+		return true
+
+	case 27: // ESC Escape
+		return true
+
+	case 28: // FS  File Separator
+		return true
+
+	case 29: // GS  Group Separator
+		return true
+
+	case 30: // RS  Record Separator
+		return true
+
+	case 31: // US  Unit Separator
+		return true
+
+	// 32 - 126 are ASCII printable characters
+
+	case 127: // Delete
+		return true
+	}
+
+	// 128 - 255 are extended ASCII codes e.g. euro sign
+}