java-native-access/jna · error · RuntimeException

Unexpected registry type {}, expected REG_BINARY

Error message

Unexpected registry type {}, expected REG_BINARY

What it means

registryGetBinaryValue first calls RegQueryValueEx with a NULL buffer to learn the value size and type, then throws this RuntimeException if the reported type is not WinNT.REG_BINARY. The library refuses to return arbitrary registry data as a byte[] when the OS says the value is of another type, so callers do not silently misinterpret DWORDs or strings as raw bytes.

Source

Thrown at contrib/platform/src/com/sun/jna/platform/win32/Advapi32Util.java:1071

     * Get a registry REG_BINARY value.
     *
     * @param hKey
     *            Parent Key.
     * @param value
     *            Name of the value to retrieve.
     * @return String value.
     */
    public static byte[] registryGetBinaryValue(HKEY hKey, String value) {
        IntByReference lpcbData = new IntByReference();
        IntByReference lpType = new IntByReference();
        int rc = Advapi32.INSTANCE.RegQueryValueEx(hKey, value, 0,
                lpType, (Pointer) null, lpcbData);
        if (rc != W32Errors.ERROR_SUCCESS
                && rc != W32Errors.ERROR_INSUFFICIENT_BUFFER) {
            throw new Win32Exception(rc);
        }
        if (lpType.getValue() != WinNT.REG_BINARY) {
            throw new RuntimeException("Unexpected registry type "
                    + lpType.getValue() + ", expected REG_BINARY");
        }
        byte[] data = new byte[lpcbData.getValue()];
        rc = Advapi32.INSTANCE.RegQueryValueEx(hKey, value, 0,
                lpType, data, lpcbData);
        if (rc != W32Errors.ERROR_SUCCESS
                && rc != W32Errors.ERROR_INSUFFICIENT_BUFFER) {
            throw new Win32Exception(rc);
        }
        return data;
    }

    /**
     * Get a registry DWORD value.
     *
     * @param root
     *            Root key.
     * @param key

View on GitHub (pinned to d036ad9781)

Solutions

  1. Read the value with registryGetValue (type-dispatching) and convert to byte[] only if it is byte[].
  2. Use the typed getter matching the actual type (registryGetStringValue, registryGetIntValue, ...).
  3. Recreate the value with type REG_BINARY (PowerShell New-ItemProperty -PropertyType Binary) if you control the writer.
  4. Catch RuntimeException and log the actual type value from the message before choosing a fallback.

Example fix

// before
byte[] blob = Advapi32Util.registryGetBinaryValue(root, key, "Config");

// after
Object v = Advapi32Util.registryGetValue(root, key, "Config");
byte[] blob = (v instanceof byte[]) ? (byte[]) v
    : (v instanceof String) ? ((String) v).getBytes(StandardCharsets.UTF_8)
    : null;
Defensive patterns

Strategy: validation

Validate before calling

Object v = Advapi32Util.registryGetValue(root, keyPath, valueName);
if (!(v instanceof byte[])) throw new IllegalStateException("Expected REG_BINARY for " + valueName);

Type guard

boolean isBinary(Object v) { return v instanceof byte[]; }

Try / catch

try { return Advapi32Util.registryGetBinaryValue(root, key, value); }
catch (RuntimeException e) { log.warn("Value {} is not REG_BINARY", value); return new byte[0]; }

Prevention

When it happens

Trigger: Calling Advapi32Util.registryGetBinaryValue(key, valueName) (or root/key/value overload) on a value stored as REG_SZ, REG_DWORD, REG_EXPAND_SZ or any type other than REG_BINARY.

Common situations: A binary blob was later managed by another tool that rewrote it as a string; assuming a GUID or packed struct value is REG_BINARY when the writer stored it as REG_SZ; schema drift between application versions.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

AI-assisted analysis of java-native-access/jna@d036ad9781 (2026-09-12). Data as JSON: /api/errors/ce6a3efbc973b3a6. Report an issue: GitHub.