pxb1988/dex2jar · critical · RuntimeException

generated different file size, planned " + size + ", but is…

Error message

generated different file size, planned " + size + ", but is " + buffer.position()

What it means

DexFileWriter.toByteArray() pre-computes the dex file size, writes all sections, then asserts the output buffer position matches the plan. A mismatch means internal size bookkeeping (padding, offsets, item sizes) drifted from what was written, so it throws before fixing the header checksum.

Solutions

Check that every custom item's calcSize/write and padding logic matches BaseItem conventions
Update the dex-writer version — this is usually an internal invariant bug
Dump the buffer (wrapDumpOut path) and compare section offsets against the plan to find the offending section

Defensive patterns

Strategy: try-catch

Try / catch

try { byte[] dex = dexFileWriter.toByteArray(); } catch (RuntimeException e) { if (e.getMessage().startsWith("generated different file size")) { /* enable dump, isolate offending item */ } throw e; }

Prevention

Never mutate items after planning offsets
Follow BaseItem size/padding conventions for custom items
Keep dex-writer up to date; regression-test full toDex() output

When it happens

Trigger: Calling toDex()/toByteArray() after adding items whose write() output does not match their calculated size (custom BaseItem subclasses, wrong alignment padding, duplicate/unregistered items).

Common situations: Extending the dex-writer with custom items or patched section writers; library bugs after adding unusual constructs (e.g. very large string/type pools, annotation with odd-length values).

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

AI-assisted analysis of pxb1988/dex2jar@b5bda4fb49 (2026-09-08). Data as JSON: /api/errors/ac2972536b77b338. Report an issue: GitHub.

Appendix: source

Thrown at dex-writer/src/main/java/com/googlecode/d2j/dex/writer/DexFileWriter.java:242

    public byte[] toByteArray() {

        // init structure for writing
        buildMapListItem();

        // place all item into file, we can know the size now
        final int size = place();

        ByteBuffer buffer = ByteBuffer.allocate(size);
        DataOut out = new ByteBufferOut(buffer);

        if (DEBUG) {
            out = wrapDumpOut(out);
        }
        // write it
        write(out);

        if (size != buffer.position()) {
            throw new RuntimeException("generated different file size, planned " + size + ", but is " + buffer.position());
        }

        // update the CRC/ sha1 checksum in dex header
        updateChecksum(buffer, size);

        return buffer.array();
    }

    public static void updateChecksum(ByteBuffer buffer, int size) {
        byte[] data = buffer.array();
        MessageDigest digest;
        try {
            digest = MessageDigest.getInstance("SHA-1");
        } catch (NoSuchAlgorithmException e) {
            throw new AssertionError();
        }

        digest.update(data, 32, size - 32);

View on GitHub (pinned to b5bda4fb49)