Verifying integrity of documents

Question

What are the steps to verify integrity of these documents ? doc,docx,docm,odt,rtf,pdf,odf,odp,xls,xlsx,xlsm,ppt,pptm

Or at least of some of them. Usually when uploaded to a content repository.

I guess that inputStream is always 99,99% read properly from MultiPart http request otherwise exception would be thrown and action taken. But user can upload already corrupted file - do I use third party libraries for checking that? I didn't see anything like that in odftoolkit, itextpdf, pdfbox, apache poi or tika

Answer 1

Go to check LibreOffice project (that already handles these archives), it has parts written in Java, and for sure you could find and use their mecanisms to check for corrupted files.

I think you can get the code from here:

http://www.libreoffice.org/get-involved/developers/

Answer 2

For all of the above listed file formats there are 3rd-party libraries which can open etc. - I don't know of a "verification only" but I think being able to open them without exceptions etc. is at least a basic check that the file is within the specified format... One such (commercial) library is Aspose - not affiliated, just a happy customer...

Answer 3

You can do checksums/hashes (that is, a secure hash) of the file before uploading, then upload the checksum separately. If the subsequently downloaded file has the same checksum, it has not been changed (to a certain high probability, depending on the checksum/hash used) from the original.

Answer 4

There are many kinds of "corrupt".

• Some corruptions should be easy to detect. For instance a truncated ODF file will most likely fail when you attempt to open it because the ZIP reader can't read it.

• Others will be literally impossible to detect. For instance a one character corruption in an RTF file will be undetectable, and so (I think) will most RTF file truncations.

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I'd be surprised if you found a single (free) tool to do this job for all of those file types, even to the extent that it is technically possible. The current generation of open source libraries for reading / writing document formats tend to focus on one family of formats only. If you are serious about this, you probably need to use a commercial library.