[jira] [Commented] (PDFBOX-5518) "Threads" array in Document Catalog should be an indirect reference

["Christian Appl (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PDFBOX-5518?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17608639#comment-17608639 ] 

Christian Appl commented on PDFBOX-5518:
----------------------------------------

I possibly should provide these changes to the PDDocumentCatalog:
!image-2022-09-23-10-54-31-618.png!

> "Threads" array in Document Catalog should be an indirect reference
> -------------------------------------------------------------------
>
>                 Key: PDFBOX-5518
>                 URL: https://issues.apache.org/jira/browse/PDFBOX-5518
>             Project: PDFBox
>          Issue Type: Bug
>          Components: PDModel
>    Affects Versions: 2.0.26
>            Reporter: Christian Appl
>            Priority: Major
>         Attachments: image-2022-09-23-09-50-30-766.png, image-2022-09-23-10-03-15-070.png, image-2022-09-23-10-54-31-618.png
>
>
> *TL;DR:*
> When using either of the methods "getThreads" or "setThreads" in class PDDocumentCatalog and saving the resulting document: Adobe Preflight is reporting an issue with the resulting "Threads" array in the document catalog and claims it should have been an indirect object reference instead of a direct object.
> My claim: The COSWriter should be able to create indirect objects for COSArrays when required.
> *Checking PDF-32000-1:*
> In table 28 "Entries in the catalog dictionary" we can find the following definition:
> !image-2022-09-23-09-50-30-766.png!
> *Determining reasons:*
> 1. The mentioned get and set methods create a COSArray for the entry "Threads" of the catalog dictionary
> 2. The COSWriter is assuming, that COSArrays should always preferably be written as a direct substructure of a dictionary.
> This may be entirely true for other arrays, but in this case is is cause for a syntactical error in resulting documents. (It is plausible and possible - but has not been checked - whether this causes issues for other structures aswell.)
> The COSWriter provides the means to create indirect objects for COSDictionaries, it however does (as far as I can see) not provide the means to flag a COSArray for the same handling.
> *Possible solutions:*
> As far as I can see the COSWriter would be entirely capable of creating COSObjects for any of the COSBase types, the only thing missing is the ability to mark a COSArray to be written indirectly and the matching handling by the COSWriter.
> Adding something like:
> !image-2022-09-23-10-03-15-070.png!
> at the right places in the COSWriter (similar to the handling of indirect COSDictionaries) seems to do the trick and resolves the issue.
> *Important issue?:*
> I fixed this on our end and hence it is not a pressing issue, also "Threads" is not as important and common as other structures and hence most documents and users won´t encounter this issue at all.
> However - It would be nice, should this be fixed.
> *Concerning a possible patch:*
> I could provide a patch making the required changes, but would have to adapt it for the current PDFBox 2.0.27-SNAPSHOT as I developed it rather as a hotfix for our mirror of the library.
> And concerning that patch I should mention:
> As can be assumed - a "isDirectArray" and "setDirectArray" method have been added to the COSArray - which is a quick and dirty solution, as it would be preferable for COSArray to use the already existing "direct" field, that other COSBase types (COSDictionaries) already use.
> As stated - the solution is quick and dirty and for a final solution in the PDFBox library a cleaner approach would be preferable. Hence I did not provide that patch for now.



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