SUP-34435 Save XMP metadata in canonical format for PDF/A documents.

Closes .NET GitHub PR 22
DEVSIX-6355

Author: carl-di-ortus

itext.tests/itext.pdfa.tests/itext/pdfa/PdfAXmpTest.cs

@@ -44,6 +44,8 @@ source product.
 using System.IO;
 using iText.Kernel.Pdf;
 using iText.Kernel.Utils;
+using iText.Kernel.XMP;
+using iText.Kernel.XMP.Options;
 using iText.Test;
 
 namespace iText.Pdfa {
@@ -95,5 +97,35 @@ public virtual void KeywordsInfoTestPdfA2b() {
             NUnit.Framework.Assert.IsNull(ct.CompareDocumentInfo(outFile, cmpFile));
             NUnit.Framework.Assert.IsNull(ct.CompareXmp(outFile, cmpFile, true));
         }
+
+        [NUnit.Framework.Test]
+        public virtual void SaveAndReadDocumentWithCanonicalXmpMetadata()
+        {
+            String outFile = destinationFolder + "saveAndReadDocumentWithCanonicalXmpMetadata.pdf";
+            PdfAConformanceLevel conformanceLevel = PdfAConformanceLevel.PDF_A_2B;
+            Stream @is = new FileStream(sourceFolder + "sRGB Color Space Profile.icm", FileMode.Open, FileAccess.Read);
+            PdfOutputIntent outputIntent = new PdfOutputIntent("Custom", "", "http://www.color.org", "sRGB IEC61966-2.1"
+                , @is);
+            PdfADocument doc = new PdfADocument(new PdfWriter(outFile), conformanceLevel, outputIntent);
+            doc.AddNewPage();
+            XMPMeta xmp = XMPMetaFactory.Create();
+            xmp.SetProperty(XMPConst.NS_PDFA_ID, XMPConst.PART, conformanceLevel.GetPart(), new PropertyOptions().SetSchemaNode(true));
+            xmp.SetProperty(XMPConst.NS_PDFA_ID, XMPConst.CONFORMANCE, conformanceLevel.GetConformance(), new PropertyOptions().SetSchemaNode(true));
+            var options = new SerializeOptions().SetUseCanonicalFormat(true).SetUseCompactFormat(false);
+            doc.SetXmpMetadata(xmp, options);
+            doc.SetTagged();
+            doc.Close();
+            PdfReader reader = new PdfReader(outFile);
+            PdfDocument resultDoc = new PdfDocument(reader);
+            PdfAConformanceLevel conformanceLevelResult = resultDoc.GetReader().GetPdfAConformanceLevel();
+            NUnit.Framework.Assert.IsNotNull(conformanceLevelResult);
+            NUnit.Framework.Assert.AreEqual(conformanceLevel.GetConformance(), conformanceLevelResult.GetConformance());
+            NUnit.Framework.Assert.AreEqual(conformanceLevel.GetPart(), conformanceLevelResult.GetPart());
+            byte[] xmpResultBytes = resultDoc.GetXmpMetadata();
+            resultDoc.Close();
+            NUnit.Framework.Assert.IsNotNull(xmpResultBytes);
+            XMPMeta xmpResult = XMPMetaFactory.ParseFromBuffer(xmpResultBytes);
+            NUnit.Framework.Assert.IsNotNull(xmpResult);
+        }
     }
 }

itext/itext.kernel/itext/kernel/pdf/PdfDocument.cs

@@ -125,6 +125,8 @@ public class PdfDocument : IEventDispatcher, IDisposable {
 
         protected internal FingerPrint fingerPrint;
 
+        protected internal SerializeOptions serializeOptions = new SerializeOptions();
+
         protected internal readonly StampingProperties properties;
 
         protected internal PdfStructTreeRoot structTreeRoot;
@@ -264,16 +266,17 @@ protected internal virtual void SetXmpMetadata(byte[] xmpMetadata) {
         }
 
         /// <summary>Sets the XMP Metadata.</summary>
+        /// <remarks>SerializeOptions are saved for the lifetime of PdfDocument.</remarks>
         /// <param name="xmpMeta">the xmpMetadata to set</param>
-        /// <param name="serializeOptions">serialization options</param>
-        public virtual void SetXmpMetadata(XMPMeta xmpMeta, SerializeOptions serializeOptions) {
-            SetXmpMetadata(XMPMetaFactory.SerializeToBuffer(xmpMeta, serializeOptions));
+        /// <param name="options">serialization options</param>
+        public virtual void SetXmpMetadata(XMPMeta xmpMeta, SerializeOptions options) {
+            serializeOptions = options;
+            SetXmpMetadata(XMPMetaFactory.SerializeToBuffer(xmpMeta, options));
         }
 
         /// <summary>Sets the XMP Metadata.</summary>
         /// <param name="xmpMeta">the xmpMetadata to set</param>
         public virtual void SetXmpMetadata(XMPMeta xmpMeta) {
-            SerializeOptions serializeOptions = new SerializeOptions();
             serializeOptions.SetPadding(2000);
             SetXmpMetadata(xmpMeta, serializeOptions);
         }
@@ -1919,6 +1922,13 @@ public virtual SequenceId GetDocumentIdWrapper() {
             return documentId;
         }
 
+        /// <summary>Sets a persistent XMP metadata serialization options.</summary>
+        /// <param name="options"><see cref="iText.Kernel.XMP.Options.SerializeOptions"/>.</param>
+        public virtual void SetSerializeOptions(SerializeOptions options)
+        {
+            serializeOptions = options;
+        }
+
         /// <summary>Gets list of indirect references.</summary>
         /// <returns>list of indirect references.</returns>
         internal virtual PdfXrefTable GetXref() {

itext/itext.kernel/itext/kernel/xmp/impl/XMPSerializerRdf.cs

@@ -803,6 +803,10 @@ private void DeclareNamespace(String prefix, String @namespace, ICollection<Stri
 					return;
 				}
 			}
+			if (string.IsNullOrEmpty(prefix))
+			{
+				return;
+			}
 			if (!usedPrefixes.Contains(prefix))
 			{
 				WriteNewline();