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From "Plamen Totev (JIRA)" <>
Subject [jira] [Created] (COMPRESS-395) Zip - Do not add data descriptor record when CRC and size value are known
Date Sat, 13 May 2017 22:05:04 GMT
Plamen Totev created COMPRESS-395:

             Summary: Zip - Do not add data descriptor record when CRC and size value are
                 Key: COMPRESS-395
             Project: Commons Compress
          Issue Type: Improvement
            Reporter: Plamen Totev
            Priority: Minor


Currently {{ZipArchiveOutputStream}} will add data descriptor record when the output do not
provide random access. But if you add an entry using {{addRawArchiveEntry}} then the CRC,
compressed size and uncompressed size could be know and there is no need for data descriptor
record as those values could be set in the local file header. The current implementation does
both - it sets the correct value in the local file header and adds additional data descriptor
record. Here is the relevant code from {{ZipArchiveOutputStream#putArchiveEntry}}:
            // just a placeholder, real data will be in data
            // descriptor or inserted later via SeekableByteChannel
            ZipEightByteInteger size = ZipEightByteInteger.ZERO;
            ZipEightByteInteger compressedSize = ZipEightByteInteger.ZERO;
            if (phased){
                size = new ZipEightByteInteger(entry.entry.getSize());
                compressedSize = new ZipEightByteInteger(entry.entry.getCompressedSize());
            } else if (entry.entry.getMethod() == STORED
                    && entry.entry.getSize() != ArchiveEntry.SIZE_UNKNOWN) {
                // actually, we already know the sizes
                size = new ZipEightByteInteger(entry.entry.getSize());
                compressedSize = size;

Maybe {{ZipArchiveOutputStream}} could be improved to not add  data descriptor record when
the CRC and size values are known in advance.

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