Add a parse method to encode illegal tag in html body

src/main/java/org/jsoup/Jsoup.java

@@ -58,6 +58,19 @@ public static Document parse(String html) {
         return Parser.parse(html, "");
     }
 
+    /**
+     Parse HTML into a Document with only legal tags by encoding illegal ones.
+     As no base URI is specified, absolute URL detection relies on the HTML including a {@code <base href>} tag.
+
+     @param html HTML to parse
+     @return sane HTML
+
+     @see #parse(String, String)
+     */
+    public static Document parseLegalTag(String html) {
+        return Parser.parseLegalTag(html, "");
+    }
+
     /**
      * Creates a new {@link Connection} to a URL. Use to fetch and parse a HTML page.
      * <p>

src/main/java/org/jsoup/parser/HtmlTreeBuilderState.java

@@ -8,6 +8,7 @@
 import org.jsoup.nodes.Element;
 import org.jsoup.nodes.Node;
 
+import java.lang.reflect.Field;
 import java.util.ArrayList;
 
 import static org.jsoup.internal.StringUtil.inSorted;
@@ -253,6 +254,20 @@ private boolean anythingElse(Token t, HtmlTreeBuilder tb) {
     },
     InBody {
         boolean process(Token t, HtmlTreeBuilder tb) {
+            if (tb.legalize) {
+                if (t.type == Token.TokenType.StartTag && !islegal(t.asStartTag().normalName)) {
+                    Token.StartTag st = t.asStartTag();
+                    Token.Character newT = new Token.Character();
+                    newT.data("<" + st.tagName + ">");
+                    t = newT;
+                } else if (t.type == Token.TokenType.EndTag && !islegal(t.asEndTag().normalName)) {
+                    Token.EndTag et = t.asEndTag();
+                    Token.Character newT = new Token.Character();
+                    newT.data("</" + et.tagName + ">");
+                    t = newT;
+                }
+            }
+
             switch (t.type) {
                 case Character: {
                     Token.Character c = t.asCharacter();
@@ -868,6 +883,38 @@ else if (!tb.onStack(formatEl)) {
             }
             return true;
         }
+
+        private boolean islegal(String tagName) {
+            try {
+                // check tags in Constants
+                Field[] fields = Constants.class.getDeclaredFields();
+                Constants _const = new Constants();
+                for (Field item: fields) {
+                    String[] tags = (String[]) item.get(_const);
+                    if (inSorted(tagName, tags))
+                        return true;
+                }
+
+                // check tags in Tag.java
+                Tag _tag = Tag.valueOf("noMeaning");
+                String[] checkList = {"blockTags", "inlineTags", "emptyTags", "formatAsInlineTags",
+                "preserveWhitespaceTags", "formListedTags", "formSubmitTags"};
+                for (String name: checkList) {
+                    Field field = Tag.class.getDeclaredField(name);
+                    field.setAccessible(true);
+                    if (inSorted(tagName, (String[]) field.get(_tag))) {
+                        field.setAccessible(false);
+                        return true;
+                    }
+                    field.setAccessible(false);
+                }
+            } catch (IllegalAccessException e) {
+                System.err.println("IllegalAccessException");
+            } catch (NoSuchFieldException e) {
+                System.err.println("NoSuchFieldException");
+            }
+            return false;
+        }
     },
     Text {
         // in script, style etc. normally treated as data tags

src/main/java/org/jsoup/parser/Parser.java

@@ -107,6 +107,19 @@ public static Document parse(String html, String baseUri) {
         return treeBuilder.parse(new StringReader(html), baseUri, new Parser(treeBuilder));
     }
 
+    /**
+     * Parse HTML into a Document with encoding illegal tags.
+     *
+     * @param html HTML to parse
+     * @param baseUri base URI of document (i.e. original fetch location), for resolving relative URLs.
+     *
+     * @return parsed Document
+     */
+    public static Document parseLegalTag(String html, String baseUri) {
+        TreeBuilder treeBuilder = new HtmlTreeBuilder();
+        return treeBuilder.parseLegalTag(new StringReader(html), baseUri, new Parser(treeBuilder));
+    }
+
     /**
      * Parse a fragment of HTML into a list of nodes. The context element, if supplied, supplies parsing context.
      *

src/main/java/org/jsoup/parser/TreeBuilder.java

@@ -22,6 +22,7 @@ abstract class TreeBuilder {
     protected String baseUri; // current base uri, for creating new elements
     protected Token currentToken; // currentToken is used only for error tracking.
     protected ParseSettings settings;
+    protected boolean legalize; // if encoding illegal tags
 
     private Token.StartTag start = new Token.StartTag(); // start tag to process
     private Token.EndTag end  = new Token.EndTag();
@@ -40,6 +41,7 @@ protected void initialiseParse(Reader input, String baseUri, Parser parser) {
         tokeniser = new Tokeniser(reader, parser.getErrors());
         stack = new ArrayList<>(32);
         this.baseUri = baseUri;
+        legalize = false;
     }
 
     Document parse(Reader input, String baseUri, Parser parser) {
@@ -55,6 +57,19 @@ Document parse(Reader input, String baseUri, Parser parser) {
         return doc;
     }
 
+    Document parseLegalTag(Reader input, String baseUri, Parser parser) {
+        initialiseParse(input, baseUri, parser);
+        this.legalize = true;
+        runParser();
+
+        reader.close();
+        reader = null;
+        tokeniser = null;
+        stack = null;
+
+        return doc;
+    }
+
     abstract List<Node> parseFragment(String inputFragment, Element context, String baseUri, Parser parser);
 
     protected void runParser() {

src/test/java/org/jsoup/parser/HtmlParserTest.java

@@ -1362,4 +1362,11 @@ public void testUNewlines() {
         doc.outputSettings().prettyPrint(false);
         assertEquals("<html><head></head><body>One  <p>Hello!</p><p>There</p></body></html> ", doc.outerHtml());
     }
+
+    @Test public void testParseLegalTag() {
+        String html = "<p>Try <aaa>jsoup</aaa></p><div><hello></div>";
+        Document doc = Jsoup.parseLegalTag(html);
+        doc.outputSettings().prettyPrint(false);
+        assertEquals("<html><head></head><body><p>Try &lt;aaa&gt;jsoup&lt;/aaa&gt;</p><div>&lt;hello&gt;</div></body></html>", doc.outerHtml());
+    }
 }