What causes "Invalid hex char '" + c + "'" in MuntashirAkon/AppManager?

Sanitize the input: strip whitespace and any "0x" prefix before decoding.

MuntashirAkon/AppManager · error · IllegalArgumentException

Invalid hex char '" + c + "'

Error message

Invalid hex char '" + c + "'

What it means

BinaryXmlPullParser.toByte() throws IllegalArgumentException when a character in a hex-encoded byte string is not a valid hex digit (0-9, A-F, a-f). It is used by hexStringToBytes when decoding TYPE_BYTES_HEX attributes.

Source

Thrown at libcore/compat/src/main/java/io/github/muntashirakon/compat/xml/BinaryXmlPullParser.java:899

                        throw new XmlPullParserException(
                                "Invalid attribute " + name + ": " + valueString);
                    }
                default:
                    throw new XmlPullParserException("Invalid conversion from " + type);
            }
        }
    }

    // NOTE: To support unbundled clients, we include an inlined copy
    // of hex conversion logic from HexDump below
    private final static char[] HEX_DIGITS =
            { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };

    private static int toByte(char c) {
        if (c >= '0' && c <= '9') return (c - '0');
        if (c >= 'A' && c <= 'F') return (c - 'A' + 10);
        if (c >= 'a' && c <= 'f') return (c - 'a' + 10);
        throw new IllegalArgumentException("Invalid hex char '" + c + "'");
    }

    static String bytesToHexString(byte[] value) {
        final int length = value.length;
        final char[] buf = new char[length * 2];
        int bufIndex = 0;
        for (int i = 0; i < length; i++) {
            byte b = value[i];
            buf[bufIndex++] = HEX_DIGITS[(b >>> 4) & 0x0F];
            buf[bufIndex++] = HEX_DIGITS[b & 0x0F];
        }
        return new String(buf);
    }

    static byte[] hexStringToBytes(String value) {
        final int length = value.length();
        if (length % 2 != 0) {
            throw new IllegalArgumentException("Invalid hex length " + length);

View on GitHub (pinned to 0152f468fc)

Solutions

Sanitize the input: strip whitespace and any "0x" prefix before decoding.
Validate with a regex ^[0-9a-fA-F]+$ before calling.
Regenerate the attribute from the original bytes if the stored value is corrupted.
Catch IllegalArgumentException around hexStringToBytes and report/recover.

Example fix

// before
byte[] b = parser.bytesToHexStringInput("0xAB CD"); // throws
// after
String hex = raw.replace("0x", "").replaceAll("\\s", "");
if (!hex.matches("[0-9a-fA-F]+")) throw new IllegalArgumentException("bad hex");
byte[] b = parseHex(hex);

Defensive patterns

Strategy: validation

Validate before calling

boolean isHex = value != null && !value.isEmpty() && value.matches("[0-9a-fA-F]+");

Try / catch

try {
    byte[] b = hexStringToBytes(value);
} catch (IllegalArgumentException e) {
    // log corrupt hex attribute, skip or regenerate
}

Prevention

Strip "0x" prefixes and whitespace before decoding hex.
Always generate hex via bytesToHexString instead of hand-rolling.
Regex-validate hex strings at input boundaries.
Never splice or trim hex strings blindly (odd-length results).

When it happens

Trigger: Calling hexStringToBytes() (directly or via reading a hex-bytes attribute) with a string containing characters outside [0-9a-fA-F], e.g. whitespace, 'g', '0x' prefixes, or dashes.

Common situations: Copy-pasted hex values with spaces or "0x" prefixes, corrupted stored attributes, or hex produced with uppercase/lowercase mixing that was further mangled by editing.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

AI-assisted analysis of MuntashirAkon/AppManager@0152f468fc (2026-09-12). Data as JSON: /api/errors/5d4f7b543c326efd. Report an issue: GitHub.