pxb1988/dex2jar · error · DexException

Magic unsupported.

Error message

Magic unsupported.

What it means

DexFileReader validates the 8-byte magic header of a .dex/.odex file when opening it. This DexException is thrown when the magic matches neither the DEX nor the ODEX signature, meaning the input stream is not a recognized Dalvik executable container at all. It fires from the public DexFileReader constructor, so any attempt to open a non-dex file fails immediately.

Solutions

1. Verify the input is actually a DEX file: unzip APKs and pass the extracted classes.dex, not the APK itself
2. Check the first 8 bytes of the file manually (hexdump -C file | head) and confirm they read 'dex\n035\0' or similar
3. Re-download or re-export the file — truncation/corruption is a frequent cause
4. Confirm you are not passing an .odex if your build only accepts plain dex (odex has its own distinct message)

Example fix

// before
DexFileReader reader = new DexFileReader(new File("app.apk")); // throws Magic unsupported
// after
try (ZipFile apk = new ZipFile("app.apk")) {
    ZipEntry dex = apk.getEntry("classes.dex");
    DexFileReader reader = new DexFileReader(apk.getInputStream(dex));
}

static boolean looksLikeDex(byte[] data) {
    byte[] magic = {'d','e','x','\n'};
    if (data == null || data.length < 8) return false;
    for (int i = 0; i < 4; i++) if (data[i] != magic[i]) return false;
    return data[7] == 0;
}
// call looksLikeDex(bytes) before new DexFileReader(bytes)

static boolean isDexFile(java.io.File f) throws java.io.IOException {
    try (java.io.RandomAccessFile raf = new java.io.RandomAccessFile(f, "r")) {
        byte[] h = new byte[8];
        if (raf.read(h) != 8) return false;
        return h[0]=='d' && h[1]=='e' && h[2]=='x' && h[3]=='\n' && h[7]==0;
    }
}

try {
    DexFileReader reader = new DexFileReader(file);
    // ...
} catch (DexException e) {
    if (e.getMessage().contains("Magic unsupported")) {
        throw new IllegalArgumentException("Not a DEX file: " + file, e);
    }
    throw e;
}

When it happens

Trigger: Calling new DexFileReader(InputStream) or DexFileReader(byte[]) with a file whose first 8 bytes are not MAGIC_DEX ("dex\n035\0" family) or MAGIC_ODEX — e.g. a .jar, a plain APK's resources, a truncated file, or a text file renamed to .dex.

Common situations: Passing an APK path where a classes.dex path is expected; feeding a .class file to the dex reader by mistake; a download corrupted or truncated so the header is garbage; picking the wrong entry out of a zip archive.

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

• Odex unsupported.
• Endian_tag unsupported
• The source file is not a .dex or .zip file
• the src file not a .dex or zip file
• Encountered RESTART_LOCAL on new v

AI-assisted analysis of pxb1988/dex2jar@b5bda4fb49 (2026-09-08). Data as JSON: /api/errors/a4a7d61586f22c65. Report an issue: GitHub.

Appendix: source

Thrown at dex-reader/src/main/java/com/googlecode/d2j/reader/DexFileReader.java:164

    /**
     * read dex from a {@link ByteBuffer}.
     * 
     * @param in
     */
    public DexFileReader(ByteBuffer in) {
        in.position(0);
        in = in.asReadOnlyBuffer().order(ByteOrder.BIG_ENDIAN);
        int magic = in.getInt() & 0xFFFFFF00;

        final int MAGIC_DEX = 0x6465780A & 0xFFFFFF00;// hex for 'dex ', ignore the 0A
        final int MAGIC_ODEX = 0x6465790A & 0xFFFFFF00;// hex for 'dey ', ignore the 0A

        if (magic == MAGIC_DEX) {
            // ok
        } else if (magic == MAGIC_ODEX) {
            throw new DexException("Odex unsupported.");
        } else {
            throw new DexException("Magic unsupported.");
        }
        int version = in.getInt() >> 8;
        if (version < DEX_035 || version > DEX_040) {
            System.err.println("Unknown DEX version. Trying anyway...");
        }
        this.dex_version = version;
        in.order(ByteOrder.LITTLE_ENDIAN);

        // skip uint checksum
        // and 20 bytes signature
        // and uint file_size
        // and uint header_size 0x70
        skip(in, 4 + 20 + 4 + 4);

        int endian_tag = in.getInt();
        if (endian_tag != ENDIAN_CONSTANT) {
            throw new DexException("Endian_tag unsupported");
        }

View on GitHub (pinned to b5bda4fb49)