Improve and fix TrueType font merging logic

DEVSIX-9257

Author: introfog

io/src/main/java/com/itextpdf/io/font/OpenTypeParser.java

@@ -197,7 +197,7 @@ static class CmapTable {
 
     private int[] glyphWidthsByIndex;
     private int[] locaTable;
-    // In case of lenient mode parsing 'name' table can be missed
+    // In case of lenient mode parsing 'name' and 'OS/2' table can be missed
     private boolean isLenientMode = false;
 
     protected HeaderTable head;
@@ -910,14 +910,17 @@ private void readHeadTable() throws java.io.IOException {
      */
     private void readOs_2Table() throws java.io.IOException {
         int[] table_location = tables.get("OS/2");
+        os_2 = new WindowsMetrics();
         if (table_location == null) {
+            if (isLenientMode) {
+                return;
+            }
             if (fileName != null) {
                 throw new IOException(IoExceptionMessageConstant.TABLE_DOES_NOT_EXISTS_IN).setMessageParams("os/2", fileName);
             } else {
                 throw new IOException(IoExceptionMessageConstant.TABLE_DOES_NOT_EXIST).setMessageParams("os/2");
             }
         }
-        os_2 = new WindowsMetrics();
         raf.seek(table_location[0]);
         int version = raf.readUnsignedShort();
         os_2.xAvgCharWidth = raf.readShort();

io/src/main/java/com/itextpdf/io/font/TrueTypeFont.java

@@ -35,7 +35,6 @@ This file is part of the iText (R) project.
 import com.itextpdf.io.util.IntHashtable;
 
 import java.util.ArrayList;
-import java.util.HashMap;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
@@ -222,7 +221,7 @@ public byte[] getSubset(Set<Integer> glyphs, boolean subsetTables) {
      */
     public static byte[] merge(Map<TrueTypeFont, Set<Integer>> toMerge, String fontName) {
         try {
-            Map<OpenTypeParser, Set<Integer>> toMergeWithParsers = new HashMap<OpenTypeParser, Set<Integer>>();
+            Map<OpenTypeParser, Set<Integer>> toMergeWithParsers = new LinkedHashMap<>();
             for (Map.Entry<TrueTypeFont, Set<Integer>> entry : toMerge.entrySet()) {
                 toMergeWithParsers.put(entry.getKey().fontParser, entry.getValue());
             }

io/src/test/java/com/itextpdf/io/font/TrueTypeFontIntegrationTest.java

@@ -24,6 +24,7 @@ This file is part of the iText (R) project.
 
 import com.itextpdf.commons.utils.MessageFormatUtil;
 import com.itextpdf.io.exceptions.IoExceptionMessageConstant;
+import com.itextpdf.test.AssertUtil;
 import com.itextpdf.test.ExtendedITextTest;
 
 import java.io.IOException;
@@ -117,4 +118,20 @@ public void tryToReadFontSubsetWithoutGlyfTableTest() throws IOException {
         String exp = MessageFormatUtil.format(IoExceptionMessageConstant.TABLE_DOES_NOT_EXIST, "glyf");
         Assertions.assertEquals(exp, e.getMessage());
     }
+
+    @Test
+    public void readFontSubsetWithoutOs2TableTest() throws IOException {
+        byte[] fontBytes = Files.readAllBytes(Paths.get(SOURCE_FOLDER + "subsetWithoutOsTable.ttf"));
+        AssertUtil.doesNotThrow(() -> FontProgramFactory.createTrueTypeFont(fontBytes, true));
+    }
+
+    @Test
+    public void tryToReadFontSubsetWithoutOs2TableTest() throws IOException {
+        byte[] fontBytes = Files.readAllBytes(Paths.get(SOURCE_FOLDER + "subsetWithoutOsTable.ttf"));
+
+        Exception e = Assertions.assertThrows(com.itextpdf.io.exceptions.IOException.class, () ->
+                FontProgramFactory.createTrueTypeFont(fontBytes, false));
+        String exp = MessageFormatUtil.format(IoExceptionMessageConstant.TABLE_DOES_NOT_EXIST, "os/2");
+        Assertions.assertEquals(exp, e.getMessage());
+    }
 }