Gets the uncompressed size of this GZIPInputStream?

Question

I have a GZIPInputStream that I constructed from another ByteArrayInputStream. I want to know the original (uncompressed) length for the gzip data.

Answer 1

Get the FileChannel from the underlying FileInputStream instead. It tells you both file size and current position of the compressed file. Example:

@Override
public void produce(final DataConsumer consumer, final boolean skipData) throws IOException {
    try (FileInputStream fis = new FileInputStream(tarFile)) {
        FileChannel channel = fis.getChannel();
        final Eta<Long> eta = new Eta<>(channel.size());
        try (InputStream is = tarFile.getName().toLowerCase().endsWith("gz")
            ? new GZIPInputStream(fis) : fis) {
            try (TarArchiveInputStream tais = (TarArchiveInputStream) new ArchiveStreamFactory()
                .createArchiveInputStream("tar", new BufferedInputStream(is))) {

                TarArchiveEntry tae;
                boolean done = false;
                while (!done && (tae = tais.getNextTarEntry()) != null) {
                    if (tae.getName().startsWith("docs/") && tae.getName().endsWith(".html")) {
                        String data = null;
                        if (!skipData) {
                            data = new String(tais.readNBytes((int) tae.getSize()), StandardCharsets.UTF_8);
                        }
                        done = !consumer.consume(data);
                    }

                    String progress = eta.toStringPeriodical(channel.position());
                    if (progress != null) {
                        System.out.println(progress);
                    }
                }
                System.out.println("tar bytes read: " + tais.getBytesRead());
            } catch (ArchiveException ex) {
                throw new IOException(ex);
            }
        }
    }
}

Answer 2

There is no reliable way to get the length other than decompressing the whole thing. See Uncompressed file size using zlib's gzip file access function .