Remove special chars from xml output

src/main/java/org/codehaus/plexus/util/xml/PrettyPrintXMLWriter.java

@@ -24,9 +24,9 @@
 import java.util.regex.Pattern;
 
 /**
- * Implementation of XMLWriter which emits nicely formatted documents.
- *
+ * <p>Implementation of XMLWriter which emits nicely formatted documents.</p>
  *
+ * <p>C0 controls chars are omitted from output</p>
  */
 public class PrettyPrintXMLWriter implements XMLWriter {
     /** Line separator ("\n" on UNIX) */
@@ -186,7 +186,7 @@ private void writeText(String text, boolean escapeXml) {
         finishTag();
 
         if (escapeXml) {
-            text = escapeXml(text);
+            text = escapeXmlText(text);
         }
 
         write(StringUtils.unifyLineSeparators(text, lineSeparator));
@@ -226,10 +226,12 @@ private static String escapeXml(String text) {
 
     private static final Pattern crlf = Pattern.compile(crlf_str);
 
-    private static final Pattern lowers = Pattern.compile("([\000-\037])");
+    private static final Pattern lowers = Pattern.compile("([\\x00-\\x1F])");
+
+    private static final Pattern illegalC0Characters = Pattern.compile("([\\x00-\\x08\\x0B-\\x0C\\x0E-\\x1F])");
 
     private static String escapeXmlAttribute(String text) {
-        text = escapeXml(text);
+        text = escapeXmlText(text);
 
         // Windows
         Matcher crlfmatcher = crlf.matcher(text);
@@ -247,6 +249,19 @@ private static String escapeXmlAttribute(String text) {
         return b.toString();
     }
 
+    private static String escapeXmlText(String text) {
+        text = escapeXml(text);
+
+        Matcher matcher = illegalC0Characters.matcher(text);
+        StringBuffer b = new StringBuffer();
+        while (matcher.find()) {
+            matcher = matcher.appendReplacement(b, "");
+        }
+        matcher.appendTail(b);
+
+        return b.toString();
+    }
+
     /** {@inheritDoc} */
     @Override
     public void addAttribute(String key, String value) {

src/main/java/org/codehaus/plexus/util/xml/pull/MXSerializer.java

@@ -24,6 +24,7 @@
  * <li>PROPERTY_SERIALIZER_INDENTATION
  * <li>PROPERTY_SERIALIZER_LINE_SEPARATOR
  * </ul>
+ * <p>C0 controls chars are omitted from output</p>
  */
 public class MXSerializer implements XmlSerializer {
     protected static final String XML_URI = "http://www.w3.org/XML/1998/namespace";
@@ -943,19 +944,9 @@ protected void writeElementContent(String text, Writer out) throws IOException {
                         // out.write(';');
                         // pos = i + 1;
                     } else {
-                        throw new IllegalStateException(
-                                "character " + Integer.toString(ch) + " is not allowed in output" + getLocation());
-                        // in XML 1.1 legal are [#x1-#xD7FF]
-                        // if(ch > 0) {
-                        // if(i > pos) out.write(text.substring(pos, i));
-                        // out.write("&#");
-                        // out.write(Integer.toString(ch));
-                        // out.write(';');
-                        // pos = i + 1;
-                        // } else {
-                        // throw new IllegalStateException(
-                        // "character zero is not allowed in XML 1.1 output"+getLocation());
-                        // }
+                        // skip special char
+                        if (i > pos) out.write(text.substring(pos, i));
+                        pos = i + 1;
                     }
                 }
                 if (seenBracket) {

src/test/java/org/codehaus/plexus/util/xml/Xpp3DomWriterTest.java

@@ -82,6 +82,12 @@ private String createExpectedXML(boolean escape) {
         buf.append(LS);
         buf.append("  </el6>");
         buf.append(LS);
+        if (escape) {
+            buf.append("  <el8>special-char-</el8>");
+        } else {
+            buf.append("  <el8>special-char-" + (char) 7 + "</el8>");
+        }
+        buf.append(LS);
         buf.append("</root>");
 
         return buf.toString();
@@ -95,7 +101,7 @@ private Xpp3Dom createXpp3Dom() {
         dom.addChild(el1);
 
         Xpp3Dom el2 = new Xpp3Dom("el2");
-        el2.setAttribute("att2", "attribute2\nnextline");
+        el2.setAttribute("att2", "attribute2\nnextline" + (char) 7);
         dom.addChild(el2);
 
         Xpp3Dom el3 = new Xpp3Dom("el3");
@@ -119,6 +125,10 @@ private Xpp3Dom createXpp3Dom() {
         el7.setValue("element7\n&\"\'<>");
         el6.addChild(el7);
 
+        Xpp3Dom el8 = new Xpp3Dom("el8");
+        el8.setValue("special-char-" + (char) 7);
+
+        dom.addChild(el8);
         return dom;
     }
 }

src/test/java/org/codehaus/plexus/util/xml/pull/MXSerializerTest.java

@@ -0,0 +1,58 @@
+package org.codehaus.plexus.util.xml.pull;
+
+import java.io.StringReader;
+import java.io.StringWriter;
+import java.util.Arrays;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class MXSerializerTest {
+
+    @Test
+    void testSerialize() throws Exception {
+
+        StringWriter writer = new StringWriter();
+
+        MXSerializer sr = new MXSerializer();
+        sr.setOutput(writer);
+
+        sr.startDocument(null, Boolean.TRUE);
+        sr.startTag(null, "root");
+        for (int i : Arrays.asList(8, 9, 10, 11, 13, 15)) {
+            sr.startTag(null, "char");
+            sr.text(Character.getName(i) + ": " + ((char) i));
+            sr.endTag(null, "char");
+        }
+
+        sr.endTag(null, "root");
+        sr.endDocument();
+        assertEquals(expectedOutput(), writer.toString());
+    }
+
+    @Test
+    void testDeserialize() throws Exception {
+        MXParser parser = new MXParser();
+        parser.setInput(new StringReader(expectedOutput()));
+        int eventType = parser.getEventType();
+
+        while (eventType != XmlPullParser.END_DOCUMENT) {
+            eventType = parser.next();
+        }
+    }
+
+    private String expectedOutput() {
+        StringBuilder out = new StringBuilder();
+        out.append("<?xml version=\"1.0\" standalone=\"yes\"?>");
+        out.append("<root>");
+        out.append("<char>BACKSPACE: </char>");
+        out.append("<char>CHARACTER TABULATION: \t</char>");
+        out.append("<char>LINE FEED (LF): \n</char>");
+        out.append("<char>LINE TABULATION: </char>");
+        out.append("<char>CARRIAGE RETURN (CR): \r</char>");
+        out.append("<char>SHIFT IN: </char>");
+        out.append("</root>");
+        return out.toString();
+    }
+}