yacy_search_server/source/net/yacy/http/CrashProtectionHandler.java

package net.yacy.http;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.eclipse.jetty.server.Handler;
import org.eclipse.jetty.server.HandlerContainer;
import org.eclipse.jetty.server.Request;
import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.server.handler.HandlerWrapper;

import net.yacy.cora.util.ConcurrentLog;

/**
 * Last-resort exception barrier wrapped around the complete handler chain.
 *
 * Note for servlet container migration: this must stay a container level
 * handler (it can not become a servlet filter): inside the servlet context a
 * filter would catch servlet exceptions before the containers error dispatch
 * and thereby replace the YaCyErrorHandler error page with a plain text stack
 * trace. Its purpose is to catch failures outside the servlet context, e.g.
 * in the transparent proxy handlers.
 */
public class CrashProtectionHandler extends HandlerWrapper implements Handler, HandlerContainer {
	
	public CrashProtectionHandler() {
		super();
	}
	
	public CrashProtectionHandler(Server s, Handler h) {
		super();
		this.setServer(s);
		this.setHandler(h);
	}
	

	@Override
	public void handle(String target, Request baseRequest, HttpServletRequest request,
			HttpServletResponse response) throws IOException, ServletException {
		try {
			super.handle(target, baseRequest, request, response);
		} catch (Exception e) {
			ConcurrentLog.severe("HTTP", "event=http.request subsystem=http result=exception method=" + request.getMethod() +
					" target=" + target + " status=500 reason=" + e.getMessage());
			// handle all we can
			writeResponse(request, response, e);
                        baseRequest.setHandled(true);
		}
	}
	
	private void writeResponse(@SuppressWarnings("unused") HttpServletRequest request, HttpServletResponse response, Exception exc) throws IOException {
            PrintWriter out;
            try { // prevent exception after partial response (only getWriter not allowed if getOutputStream called before; Servlet API 3.0 )
                out = response.getWriter();
            } catch (IllegalStateException e) {
                out = new PrintWriter(response.getOutputStream());
            }
            out.println("Ops!");
            out.println();
            out.println("Message: " + exc.getMessage());
            exc.printStackTrace(out);
            response.setContentType("text/plain");
            response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
	}
}