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https://issues.apache.org/jira/browse/PDFBOX-5683?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17766767#comment-17766767
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Patrick Dalla Bernardina edited comment on PDFBOX-5683 at 9/19/23 11:52 AM:
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Other difficulty: For testing I implemented a Reference Document field, as such
that if the resource is not found in the document, it would be loaded from the
reference document. But i've noticed that COSObject does not implement equals
or hash methods, so it could not easyly find the resource using the "indirect"
reference from the crashed document.
For the case of using a reference document, this could be enough.
Although, with no reference document, other way to find an alternative should
be used. Certainly some other document data (metadata) could help to suggest
this alternative. So the resource cache resolution must have a reference to the
document.
was (Author: patrickdalla):
Other difficulty: For testing I implemented a Reference Document field, as such
that if the resource is not found in the document, it would be loaded from the
reference document. But i've noticed that COSObject does not implement equals
or hash methods, so it could not easyly find the resource using the "indirect"
reference from the crashed document.
> Inconsistent/incomplete PDF rendering
> -------------------------------------
>
> Key: PDFBOX-5683
> URL: https://issues.apache.org/jira/browse/PDFBOX-5683
> Project: PDFBox
> Issue Type: New Feature
> Components: Parsing
> Reporter: Patrick Dalla Bernardina
> Priority: Minor
> Labels: Forensic
> Attachments: pdf1.pdf
>
> Original Estimate: 72h
> Remaining Estimate: 72h
>
> We have integrated tika and its default parsers in a Forensic Tool (IPED). As
> a forensic tool, it tries to recover/carve deleted PDF files, some of which
> can be partially recovered.
> PDFParser throws Exception if there is no PDF version header on the parsed
> content, avoiding any further content parsing.
> Commenting this exception, the parser still throws the exception "Missing
> root object specification in trail" in initialParse method, as this root
> object is normally at begin of a PDF file.
> Although, I could made some simple effort to build a "fake" root
> COSDictionary and build the PAGES entry with the recoverable PAGEs, searching
> them from document.getXrefTable();
> {code:java}
> protected void initialParse() throws IOException
> {
> COSDictionary trailer = retrieveTrailer();
>
> COSDictionary root = trailer.getCOSDictionary(COSName.ROOT);
> if (root == null)
> {
> // rebuild root from xref recovered info
> root = new COSDictionary();
> root.setItem(COSName.TYPE, COSName.CATALOG);
> trailer.setItem(COSName.ROOT, root);
> // identify recovered pages from xref to mount COSName.PAGES
> Map<COSObjectKey, Long> xrefTable = document.getXrefTable();
> COSArray kids = new COSArray();
> for (Entry<COSObjectKey, Long> e : xrefTable.entrySet()) {
> COSObject o = document.getObjectFromPool(e.getKey());
> if (o.getObject() instanceof COSDictionary) {
> COSDictionary d = (COSDictionary) o.getObject();
> COSName type = d.getCOSName(COSName.TYPE);
> if (type != null) {
> if (type.equals(COSName.PAGE)) {
> kids.add(d);
> }
> }
> }
> }
>
> COSDictionary pages = new COSDictionary();
> pages.setItem(COSName.TYPE, COSName.PAGES);
> pages.setItem(COSName.COUNT, COSInteger.get(kids.size()));
> pages.setItem(COSName.KIDS, kids);
> document.setDecrypted();
> root.setItem(COSName.PAGES, pages);
> initialParseDone = true;
> return;
> // throw new IOException("Missing root object specification in
> trailer.");
> }
> // in some pdfs the type value "Catalog" is missing in the root object
> if (isLenient() && !root.containsKey(COSName.TYPE))
> {
> root.setItem(COSName.TYPE, COSName.CATALOG);
> }
> // check pages dictionaries
> checkPages(root);
> document.setDecrypted();
> initialParseDone = true;
> }
> {code}
> This simple effort was enough to show the recoverable pages on PDFDebugger,
> export XMP metadatas, text, and get the rendered pages buffered images to use
> on my OCR module.
> So, it would be very useful if PDFBOX already have some optional
> parameterizable mode to open/recover inconsistent/incomplete pdf file, with
> at least the implementation above or further recover actions.
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