Fix xref 0 entry index retrieval when reading file

DEVSIX-1428

Autoported commit.
Original commit hash: [ff82dd031]

Author: Benoit Lagae

itext.tests/itext.kernel.tests/itext/kernel/pdf/PdfXrefTableTest.cs

@@ -0,0 +1,102 @@
+/*
+* To change this license header, choose License Headers in Project Properties.
+* To change this template file, choose Tools | Templates
+* and open the template in the editor.
+*/
+using System;
+using iText.Test;
+
+namespace iText.Kernel.Pdf {
+    /// <author>benoit</author>
+    public class PdfXrefTableTest : ExtendedITextTest {
+        public static readonly String sourceFolder = iText.Test.TestUtil.GetParentProjectDirectory(NUnit.Framework.TestContext
+            .CurrentContext.TestDirectory) + "/resources/itext/kernel/pdf/PdfXrefTableTest/";
+
+        public static readonly String destinationFolder = NUnit.Framework.TestContext.CurrentContext.TestDirectory
+             + "/test/itext/kernel/pdf/PdfXrefTableTest/";
+
+        [NUnit.Framework.OneTimeSetUp]
+        public static void BeforeClass() {
+            ITextTest.CreateOrClearDestinationFolder(destinationFolder);
+        }
+
+        /// <exception cref="System.IO.IOException"/>
+        [NUnit.Framework.Test]
+        public virtual void TestCreateAndUpdateXMP() {
+            String created = destinationFolder + "testCreateAndUpdateXMP_create.pdf";
+            String updated = destinationFolder + "testCreateAndUpdateXMP_update.pdf";
+            PdfDocument pdfDocument = new PdfDocument(new PdfWriter(created));
+            pdfDocument.AddNewPage();
+            pdfDocument.GetXmpMetadata(true);
+            // create XMP metadata
+            pdfDocument.Close();
+            pdfDocument = new PdfDocument(new PdfReader(created), new PdfWriter(updated));
+            pdfDocument.Close();
+            pdfDocument = new PdfDocument(new PdfReader(updated));
+            PdfXrefTable xref = pdfDocument.GetXref();
+            PdfIndirectReference freeRef = xref.Get(xref.Size() - 2);
+            // 6
+            /*
+            Current xref structure:
+            xref
+            0 8
+            0000000006 65535 f % this is object 0; 6 refers to free object 6
+            0000000203 00000 n
+            0000000510 00000 n
+            0000000263 00000 n
+            0000000088 00000 n
+            0000000015 00000 n
+            0000000000 00001 f % this is object 6; 0 refers to free object 0; note generation number
+            0000000561 00000 n
+            */
+            NUnit.Framework.Assert.IsTrue(freeRef.IsFree());
+            NUnit.Framework.Assert.AreEqual(xref.Get(0).offsetOrIndex, freeRef.objNr);
+            NUnit.Framework.Assert.AreEqual(1, freeRef.genNr);
+            pdfDocument.Close();
+        }
+
+        /// <exception cref="System.IO.IOException"/>
+        [NUnit.Framework.Test]
+        public virtual void TestCreateAndUpdateTwiceXMP() {
+            String created = destinationFolder + "testCreateAndUpdateTwiceXMP_create.pdf";
+            String updated = destinationFolder + "testCreateAndUpdateTwiceXMP_update.pdf";
+            String updatedAgain = destinationFolder + "testCreateAndUpdateTwiceXMP_updatedAgain.pdf";
+            PdfDocument pdfDocument = new PdfDocument(new PdfWriter(created));
+            pdfDocument.AddNewPage();
+            pdfDocument.GetXmpMetadata(true);
+            // create XMP metadata
+            pdfDocument.Close();
+            pdfDocument = new PdfDocument(new PdfReader(created), new PdfWriter(updated));
+            pdfDocument.Close();
+            pdfDocument = new PdfDocument(new PdfReader(updated), new PdfWriter(updatedAgain));
+            pdfDocument.Close();
+            pdfDocument = new PdfDocument(new PdfReader(updatedAgain));
+            PdfXrefTable xref = pdfDocument.GetXref();
+            PdfIndirectReference freeRef1 = xref.Get(xref.Size() - 3);
+            // 6
+            PdfIndirectReference freeRef2 = xref.Get(xref.Size() - 2);
+            // 7
+            /*
+            Current xref structure:
+            xref
+            0 9
+            0000000006 65535 f % this is object 0; 6 refers to free object 6
+            0000000203 00000 n
+            0000000510 00000 n
+            0000000263 00000 n
+            0000000088 00000 n
+            0000000015 00000 n
+            0000000007 00002 f % this is object 6; 7 refers to free object 7; note generation number
+            0000000000 00001 f % this is object 7; 0 refers to free object 0; note generation number
+            0000000561 00000 n
+            */
+            NUnit.Framework.Assert.IsTrue(freeRef1.IsFree());
+            NUnit.Framework.Assert.AreEqual(xref.Get(0).offsetOrIndex, freeRef1.objNr);
+            NUnit.Framework.Assert.AreEqual(2, freeRef1.genNr);
+            NUnit.Framework.Assert.IsTrue(freeRef2.IsFree());
+            NUnit.Framework.Assert.AreEqual(freeRef1.offsetOrIndex, freeRef2.objNr);
+            NUnit.Framework.Assert.AreEqual(1, freeRef2.genNr);
+            pdfDocument.Close();
+        }
+    }
+}

itext/itext.kernel/itext/kernel/pdf/PdfReader.cs

@@ -917,7 +917,12 @@ protected internal virtual PdfDictionary ReadXrefSection() {
                             reference.ClearState(PdfObject.READING);
                         }
                         else {
-                            continue;
+                            if (reference.objNr == 0 && pos != 0L) {
+                                reference.SetIndex(pos);
+                            }
+                            else {
+                                continue;
+                            }
                         }
                     }
                     if (tokens.TokenValueEqualsTo(PdfTokenizer.N)) {

itext/itext.kernel/itext/kernel/pdf/PdfXrefTable.cs

@@ -116,7 +116,6 @@ internal virtual PdfIndirectReference CreateNewIndirectReference(PdfDocument doc
         }
 
         protected internal virtual void FreeReference(PdfIndirectReference reference) {
-            reference.SetOffset(0);
             reference.SetState(PdfObject.FREE);
             if (!reference.CheckState(PdfObject.FLUSHED)) {
                 if (reference.refersTo != null) {

port-hash

@@ -1 +1 @@
-e029f7c146b1cdabda9d177dac98a423d5d770cb
+ff82dd0311e7e051ca7a79f28d309553ccaba7ea