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Does anyone have any ideas for how to pragmatically quickly check if a zip file is corrupted based on file size? Ideally the best way to check if a zip is corrupted is to do a CRC check but this can take a long time especially if there is a lot of large zip files. I would be happy just to be able to do a quick file size or header check.
Thanks in advance.
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ZIP files can get corrupted during the download process. If the download was interrupted, due to a power outage or an unexpected program closure even for a moment, unreadable data can end up becoming part of the downloaded ZIP file and make it difficult for the data to be extracted.
The best solution to the problem of a damaged Zip file is to try to obtain another copy of the file. For example, use your backup copy of the file or get a new copy from the original source. If you obtained the Zip file by downloading it, then downloading it again may solve the problem.
Your code is basically OK, try to find out which file is responsible for the corrupted zip file. Check whether digitalFile. getFile() always returns a valid and accessible argument to FileInputStream. Just add a bit logging to your code and you will find out what's wrong.
Use zip -T to test the the file corrupted or not. Sample corrupted file look like this:
zip -T filename.zip
zip warning: missing end signature--probably not a zip file (did you
zip warning: remember to use binary mode when you transferred it?)
zip warning: (if you are trying to read a damaged archive try -F)
zip error: Zip file structure invalid (filename.zip)
DotNetZip, a free open source library for handling zip files in .NET languages, supports a CheckZip() method that does what you want. There are various levels of assurance available at your option. The basic level just checks consistency of metadata. The most complete level does a full extraction of the zip file into a bitbucket to verify that the actual compressed data is not corrupted.
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