无法使用 SHA-256 创建 checkSum 值

Question

As per my requirement I want to create checksum value using SHA-256, from InputStream,

As below:

private InputStream createZipInput(List<ResponsePack> aList, byte[] manifestData)
    {
        final int bufferSize = 2048;
        byte buffer[] = new byte[bufferSize];
        ByteArrayOutputStream byteStream = new ByteArrayOutputStream();
        ZipOutputStream zipFileToSend = new ZipOutputStream(byteStream);
        LOG.trace("Compressing the file {}");
        try
        {
            for (ResponsePack info : aList)
            {
                ByteArrayOutputStream byteStreamCheckSum = new ByteArrayOutputStream();
                ZipOutputStream zipFileToSendCheckSum = new ZipOutputStream(byteStreamCheckSum);
                zipFileToSend.putNextEntry(new ZipEntry(info.getFileName()));
                zipFileToSendCheckSum.putNextEntry(new ZipEntry(info.getFileName()));
                InputStream in = info.getFileContentStream();
                int length;
                while ((length = in.read(buffer)) >= 0)
                {
                    zipFileToSend.write(buffer, 0, length);
                    zipFileToSendCheckSum.write(buffer, 0, length);
                }
                zipFileToSend.closeEntry();
                zipFileToSendCheckSum.closeEntry();
                String checksum = validChecksum(byteStreamCheckSum.toByteArray());
                LOG.error("Checksum {}", checksum);
                zipFileToSendCheckSum.flush();
                zipFileToSendCheckSum.close();
            }
            zipFileToSend.close();
        }
        catch (IOException e)
        {
            return e;
        }
        return new ByteArrayInputStream(byteStream.toByteArray());
    }
    
    private static String validChecksum(byte[] dataCopy)
    {
        printLOG("Byte Array Size {}", dataCopy.length);
        try (ZipInputStream zipInputStream = new ZipInputStream(new ByteArrayInputStream(dataCopy)))
        {
            ZipEntry zipEntry;
            MessageDigest digest = DigestUtils.getSha256Digest();
            DWriter writer = new DWriter(digest);
            while ((zipEntry = zipInputStream.getNextEntry()) != null)
            {
                org.apache.commons.io.output.ByteArrayOutputStream dest = StreamUtils.extractFileAsByteArrayStream(zipInputStream);
                LOG.error("CheckSum Entity creating");
                if(zipEntry != null)
                {
                    printLOG("CheckSum Entity file Name {}", zipEntry.getName());
                }
                LOG.error("Byte array size {}", dest.toByteArray().length);
                writer.write(dest.toByteArray());
                dest.flush();
                dest.close();
            }
            
            if (writer.getChecksum() != null)
            {
                return writer.getChecksum();
            }
            else
            {
                return "";
            }
        }
        catch (Exception e)
        {
            printLOG("Exception encountered while creating checksum: {}", e.getMessage());
            return "";
        }
    }
    
    static class DWriter
    {
        private final MessageDigest myDigest;

        DWriter(MessageDigest digest)
        {
            myDigest = digest;
        }

        public void write(byte[] data)
        {
            myDigest.update(data);
        }

        public String getChecksum()
        {
            return new String(Hex.encodeHex(myDigest.digest()));
        }
    }

But the problem is when I checked the log, found byte array contains value but still checksum always creating for empty string, as below

Byte Array Size 3948
CheckSum Entity creating
CheckSum Entity file Name 20200911104812526.json
Byte array size 20854
Checksum e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855

Help me where I am doing wrong, due to which I am getting checksum for an empty string

Answer 1

I'm not sure what's wrong with the code but it seems overly complicated: you're writing the input into a zipped stream and the dezip it in memory to read it again.

You don't need to do that: storing the input in a (non-zipped) byte array should be enough.

I think you need to make sure that in.read() works as intended (and that there's actually some data to read). You get the checksum for a null input and your zip entry is also empty, so it looks like the input was empty. Add some logs or use a debugger to investigate what's happening.

private InputStream createZipInput(List<ResponsePack> aList, byte[] manifestData) {
    final int bufferSize = 2048;
    byte buffer[] = new byte[bufferSize];
    ByteArrayOutputStream byteStream = new ByteArrayOutputStream();
    ZipOutputStream zipFileToSend = new ZipOutputStream(byteStream);
    LOG.trace("Compressing the file {}");
    try {
        for (ResponsePack info : aList) {
            ByteArrayOutputStream byteStreamCheckSum = new ByteArrayOutputStream();
            zipFileToSend.putNextEntry(new ZipEntry(info.getFileName()));
            InputStream in = info.getFileContentStream();
            int length;
            while ((length = in.read(buffer)) != -1) {
                zipFileToSend.write(buffer, 0, length);
                byteStreamCheckSum.write(buffer, 0, length);
            }
            zipFileToSend.closeEntry();
            
            MessageDigest digest = DigestUtils.getSha256Digest();
            digest.update(byteStreamCheckSum.toByteArray());
            String checksum = new String(Hex.encodeHex(digest.digest()));
            
            LOG.error("Checksum {}", checksum);
            
        }
        zipFileToSend.close();
    } catch (IOException e) {
        throw e;
    }
    return new ByteArrayInputStream(byteStream.toByteArray());