pxb1988/dex2jar · error · IOException

the src file not a .dex or zip file

Error message

the src file not a .dex or zip file

What it means

ZipUtil.readDex(byte[]) throws IOException as its final fallback when the input bytes match neither the 'dex' magic nor the 'PK' zip prefix, so there is no supported way to obtain classes.dex from the data. Only raw dex bytes and zip containers are accepted.

Solutions

  1. Verify the file type with magic bytes (file command) before calling readDex.
  2. Decompress if the content is gzip/deflate, then retry.
  3. Fix the download path if you received HTML/text instead of a binary artifact.
  4. For non-dex binaries (.so/.odex/.vdex), use an appropriate converter first or pass real dex bytes.

Example fix

// before
byte[] dex = ZipUtil.readDex(mysteryBytes);
// after
String magic = new String(mysteryBytes, 0, 3, StandardCharsets.ISO_8859_1);
if (!magic.startsWith("dex") && !magic.startsWith("PK")) {
    throw new IllegalArgumentException("not a dex/zip: magic=" + magic);
}
byte[] dex = ZipUtil.readDex(mysteryBytes);
Defensive patterns

Strategy: validation

Validate before calling

String magic = data.length >= 3 ? new String(data, 0, 3, StandardCharsets.ISO_8859_1) : "";
if (!magic.startsWith("dex") && !magic.startsWith("PK")) {
    throw new IllegalArgumentException("readDex requires dex/zip, got magic=" + magic);
}

Type guard

static boolean isDexOrZip(byte[] d) {
    return d != null && d.length >= 3 &&
        (new String(d, 0, 3, StandardCharsets.ISO_8859_1).startsWith("dex") ||
         new String(d, 0, 2, StandardCharsets.ISO_8859_1).equals("PK"));
}

Try / catch

try {
    byte[] dex = ZipUtil.readDex(data);
} catch (IOException e) {
    LOG.error("unsupported input format: " + e.getMessage());
}

Prevention

When it happens

Trigger: Calling ZipUtil.readDex on data whose first bytes are not 'dex' or 'PK' — ELF shared libraries, gzip streams, XML resources, HTML error pages from failed downloads.

Common situations: Passing an .odex/.vdex or lib*.so file where a dex was intended; a gzip-compressed dex not decompressed first; a download that saved an HTML error page instead of the APK.

Understand the failure class

Background: "is not a compatible type" / "cannot merge" errors: when a value's type doesn't match what the library requires — this error's family across 65 libraries.

Related errors

AI-assisted analysis of pxb1988/dex2jar@b5bda4fb49 (2026-09-08). Data as JSON: /api/errors/75100608ad475d0a. Report an issue: GitHub.

Appendix: source

Thrown at dex-reader/src/main/java/com/googlecode/d2j/reader/zip/ZipUtil.java:89

     * @throws IOException
     */
    public static byte[] readDex(byte[] data) throws IOException {
        if (data.length < 3) {
            throw new IOException("File too small to be a dex/zip");
        }
        if ("dex".equals(new String(data, 0, 3, StandardCharsets.ISO_8859_1))) {// dex
            return data;
        } else if ("PK".equals(new String(data, 0, 2, StandardCharsets.ISO_8859_1))) {// ZIP
            try (ZipFile zipFile = new ZipFile(data)) {
                ZipEntry classes = zipFile.findFirstEntry("classes.dex");
                if (classes != null) {
                    return toByteArray(zipFile.getInputStream(classes));
                } else {
                    throw new IOException("Can not find classes.dex in zip file");
                }
            }
        }
        throw new IOException("the src file not a .dex or zip file");
    }
}

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