Correct XMP URI serialisation in PDF/UA ext schema

URIs and text follow different conventions in the XMP data model. While
many parsers tolerate URIs encoded as text, it's technically not
allowed.

pdfa/src/main/java/com/itextpdf/pdfa/PdfAXMPUtil.java

@@ -54,7 +54,7 @@ public class PdfAXMPUtil {
                     "          <pdfaExtension:schemas>\n" +
                     "            <rdf:Bag>\n" +
                     "              <rdf:li rdf:parseType=\"Resource\">\n" +
-                    "                <pdfaSchema:namespaceURI>http://www.aiim.org/pdfua/ns/id/</pdfaSchema:namespaceURI>\n" +
+                    "                <pdfaSchema:namespaceURI rdf:resource=\"http://www.aiim.org/pdfua/ns/id/\"/>\n" +
                     "                <pdfaSchema:prefix>pdfuaid</pdfaSchema:prefix>\n" +
                     "                <pdfaSchema:schema>PDF/UA identification schema</pdfaSchema:schema>\n" +
                     "                <pdfaSchema:property>\n" +

pdfa/src/test/java/com/itextpdf/pdfa/PdfAXmpTest.java

@@ -42,23 +42,23 @@ This file is part of the iText (R) project.
  */
 package com.itextpdf.pdfa;
 
-import com.itextpdf.kernel.pdf.PdfAConformanceLevel;
-import com.itextpdf.kernel.pdf.PdfDocument;
-import com.itextpdf.kernel.pdf.PdfOutputIntent;
-import com.itextpdf.kernel.pdf.PdfReader;
-import com.itextpdf.kernel.pdf.PdfWriter;
+import com.itextpdf.io.source.ByteArrayOutputStream;
+import com.itextpdf.kernel.pdf.*;
 import com.itextpdf.kernel.utils.CompareTool;
 import com.itextpdf.kernel.xmp.XMPConst;
 import com.itextpdf.kernel.xmp.XMPException;
 import com.itextpdf.kernel.xmp.XMPMeta;
 import com.itextpdf.kernel.xmp.XMPMetaFactory;
+import com.itextpdf.kernel.xmp.options.ParseOptions;
 import com.itextpdf.kernel.xmp.options.PropertyOptions;
 import com.itextpdf.kernel.xmp.options.SerializeOptions;
+import com.itextpdf.kernel.xmp.properties.XMPProperty;
 import com.itextpdf.test.ExtendedITextTest;
 import com.itextpdf.test.annotations.type.IntegrationTest;
-import java.io.FileInputStream;
-import java.io.IOException;
-import java.io.InputStream;
+
+import java.io.*;
+import java.nio.charset.StandardCharsets;
+
 import org.junit.Assert;
 import org.junit.BeforeClass;
 import org.junit.Test;
@@ -147,6 +147,57 @@ public void saveAndReadDocumentWithCanonicalXmpMetadata() throws IOException, XM
         }
     }
 
+    @Test
+    public void testPdfUAExtensionMetadata() throws IOException {
+
+        String outFile = destinationFolder + "testPdfUAExtensionMetadata.pdf";
+        String cmpFile = cmpFolder + "cmp_testPdfUAExtensionMetadata.pdf";
+
+        try (FileOutputStream fos = new FileOutputStream(outFile)) {
+            generatePdfAWithUA(fos);
+        }
+
+        CompareTool ct = new CompareTool();
+        Assert.assertNull(ct.compareXmp(outFile, cmpFile, true));
+
+    }
+
+    @Test
+    public void testPdfUAIdSchemaNameSpaceUriIsNotText() throws IOException {
+        ByteArrayOutputStream baos = new ByteArrayOutputStream();
+        generatePdfAWithUA(baos);
+
+        // check whether the pdfuaid NS URI was properly encoded as a URI with rdf:resource
+        PdfDocument readDoc = new PdfDocument(new PdfReader(new ByteArrayInputStream(baos.toByteArray())));
+        String xmpString = new String(readDoc.getXmpMetadata(), StandardCharsets.UTF_8);
+        Assert.assertTrue(
+                "Did not find expected namespaceURI definition",
+                xmpString.contains("<pdfaSchema:namespaceURI rdf:resource=\"http://www.aiim.org/pdfua/ns/id/\"/>")
+        );
+
+    }
+
+    private void generatePdfAWithUA(OutputStream os) throws IOException {
+        WriterProperties wp = new WriterProperties().addUAXmpMetadata();
+        try (PdfWriter w = new PdfWriter(os, wp)) {
+            PdfOutputIntent outputIntent;
+            try (InputStream is = new FileInputStream(sourceFolder + "sRGB Color Space Profile.icm")) {
+                outputIntent = new PdfOutputIntent(
+                        "Custom", "",
+                        "http://www.color.org",
+                        "sRGB IEC61966-2.1",
+                        is
+                );
+            }
+            PdfDocument pdfDoc = new PdfADocument(w, PdfAConformanceLevel.PDF_A_2A, outputIntent).setTagged();
+            pdfDoc.getDocumentInfo().setTitle("Test document");
+            pdfDoc.getCatalog().setViewerPreferences(new PdfViewerPreferences().setDisplayDocTitle(true));
+            pdfDoc.getCatalog().setLang(new PdfString("en"));
+            pdfDoc.addNewPage();
+            pdfDoc.close();
+        }
+    }
+
     private int count(byte[] array, byte b) {
         int counter = 0;
         for (byte each : array) {