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fix resolving compressed objects in additional cross-reference table #452

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fix resolving compressed objects in additional cross-reference table #452

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25 changes: 20 additions & 5 deletions PdfSharpCore/Pdf.IO/Parser.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1271,11 +1271,26 @@ private PdfTrailer ReadXRefStream(PdfCrossReferenceTable xrefTable)
ReadSymbol(Symbol.BeginStream);
ReadStream(xrefStream);

//xrefTable.Add(new PdfReference(objectID, position));
PdfReference iref = new PdfReference(xrefStream);
iref.ObjectID = objectID;
iref.Value = xrefStream;
xrefTable.Add(iref);
// An additional cross-reference (/Prev) could have been referenced in the first cross-reference by position.
// That goes into item.Type == 1 below and adds its objectID into the xrefTable with just a position and no value.
// Then we can't just do `xrefTable.Add(iref)` because that is a no-op when the objectID is already present in the ObjectTable.
// Making sure that the iref.Value is set here correctly ensure that the mechanisms in PdfReader will work correctly:
// 1. It needs to find a PdfCrossReferenceStream in iref.Value in order to resolve compressed objects.
// 2. If we leave null in iref.Value it would do redundant parsing to resolve the value again.
if (xrefTable.ObjectTable.TryGetValue(objectID, out PdfReference iref))
{
if (iref.Value == null)
{
iref.Value = xrefStream;
}
}
else
{
iref = new PdfReference(xrefStream);
iref.ObjectID = objectID;
iref.Value = xrefStream;
xrefTable.Add(iref);
}

Debug.Assert(xrefStream.Stream != null);
//string sValue = new RawEncoding().GetString(xrefStream.Stream.UnfilteredValue,);
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