MuntashirAkon/AppManager · error · IOException

Gzip-compressed data is corrupt (uncompressed size mismatch)

Error message

Gzip-compressed data is corrupt (uncompressed size mismatch)

What it means

The .gz trailer also stores ISIZE, the uncompressed length modulo 2^32. read() throws IOException when the stored ISIZE differs from the number of bytes the inflater actually produced, meaning the decoded payload length does not match the member's declared size.

Solutions

  1. Recover the original file; the member is internally inconsistent and the data cannot be trusted.
  2. If handling concatenated members, enable decompressConcatenated=true so member boundaries are parsed correctly.
  3. Recompress with standard gzip/zlib if a custom tool produced the wrong ISIZE.

Example fix

// before
GzipCompressorInputStream gz = new GzipCompressorInputStream(in);
// after (multi-member files)
GzipCompressorInputStream gz = new GzipCompressorInputStream(in, true);
Defensive patterns

Strategy: try-catch

Try / catch

try (InputStream gz = new GzipCompressorInputStream(rawIn, true)) {
    IOUtils.copy(gz, out);
} catch (IOException e) {
    if (e.getMessage().contains("uncompressed size mismatch")) {
        // ISIZE disagrees with decoded bytes — treat the archive as damaged
        throw new IOException("gzip member size mismatch; re-acquire archive", e);
    }
    throw e;
}

Prevention

When it happens

Trigger: Truncated or extended deflate data; a trailer from a different member (mis-joined concatenated members); corruption of the last 8 bytes; custom compressors writing wrong ISIZE.

Common situations: Concatenating .gz files by naive byte concatenation without concatenated-mode enabled or with damaged boundaries; interrupted writes leaving a partial member with a stale trailer; non-conforming compression tools.

Understand the failure class

Background: Checksum mismatch errors: "checksum verification failed", "digest mismatch", "expected vs actual checksum" — what they mean and how to fix them — this error's family across 41 libraries.

Related errors

AI-assisted analysis of MuntashirAkon/AppManager@0152f468fc (2026-09-12). Data as JSON: /api/errors/a772b0890515804f. Report an issue: GitHub.

Appendix: source

Thrown at app/src/main/java/org/apache/commons/compress/compressors/gzip/GzipCompressorInputStream.java:331

                    throw new IOException();
                }

                bufUsed = 0;

                final DataInput inData = new DataInputStream(in);

                // CRC32
                final long crcStored = ByteUtils.fromLittleEndian(inData, 4);

                if (crcStored != crc.getValue()) {
                    throw new IOException("Gzip-compressed data is corrupt (CRC32 error)");
                }

                // Uncompressed size modulo 2^32 (ISIZE in the spec)
                final long isize = ByteUtils.fromLittleEndian(inData, 4);

                if (isize != (inf.getBytesWritten() & 0xffffffffL)) {
                    throw new IOException("Gzip-compressed data is corrupt (uncompressed size mismatch)");
                }

                // See if this is the end of the file.
                if (!decompressConcatenated || !init(false)) {
                    inf.end();
                    inf = null;
                    endReached = true;
                    return size == 0 ? -1 : size;
                }
            }
        }

        return size;
    }

    /**
     * Checks if the signature matches what is expected for a .gz file.
     *

View on GitHub (pinned to 0152f468fc)