hudson.util.TableNestChecker Maven / Gradle / Ivy

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package hudson.util;

import org.xml.sax.helpers.XMLFilterImpl;
import org.xml.sax.XMLFilter;
import org.xml.sax.ContentHandler;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.apache.commons.jelly.XMLOutput;

import java.util.Stack;
import java.util.Map;
import java.util.HashMap;
import java.util.Set;
import java.util.HashSet;
import java.util.Arrays;

/**
 * {@link XMLFilter} that checks the proper nesting of table related tags.
 *
 * 
 * Browser often "fixes" HTML by moving tables into the right place,
 * so failure to generate proper tables can result in a hard-to-track bugs.
 *
 * 
 * TODO: where to apply this in stapler?
 * JellyClassTearOff creates XMLOutput. Perhaps we define a decorator?
 * We can also wrap Script. would that work better?
 *
 * @author Kohsuke Kawaguchi
 */
public class TableNestChecker extends XMLFilterImpl {

    private final Stack elements = new Stack();
    private final Stack tagNames = new Stack();

    public static void applyTo(XMLOutput xo) {
        xo.setContentHandler(new TableNestChecker(xo.getContentHandler()));
    }

    public TableNestChecker() {
        elements.push(ALL_ALLOWED);
    }

    public TableNestChecker(ContentHandler target) {
        this();
        setContentHandler(target);
    }

    public void startElement(String uri, String localName, String qName, Attributes atts) throws SAXException {
        String tagName = localName.toUpperCase();

        // make sure that this tag occurs in the proper context
        if(!elements.peek().isAllowed(tagName))
            throw new SAXException(tagName+" is not allowed inside "+tagNames.peek());

        Checker next = CHECKERS.get(tagName);
        if(next==null)  next = ALL_ALLOWED;
        elements.push(next);
        tagNames.push(tagName);

        super.startElement(uri, localName, qName, atts);
    }

    public void endElement(String uri, String localName, String qName) throws SAXException {
        elements.pop();
        tagNames.pop();
        super.endElement(uri, localName, qName);
    }


    private interface Checker {
        boolean isAllowed(String childTag);
    }

    private static final Checker ALL_ALLOWED = new Checker() {
        public boolean isAllowed(String childTag) {
            return true;
        }
    };

    private static final class InList implements Checker {
        private final Set tags;

        private InList(String... tags) {
            this.tags = new HashSet(Arrays.asList(tags));
        }

        public boolean isAllowed(String childTag) {
            return tags.contains(childTag);
        }
    }

    private static final Map CHECKERS = new HashMap();

    static {
        CHECKERS.put("TABLE",new InList("TR","THEAD","TBODY"));
        InList rows = new InList("TR");
        CHECKERS.put("THEAD",rows);
        CHECKERS.put("THEAD",rows);
        CHECKERS.put("TR",   new InList("TD","TH"));
    }
}