Replace the stock Jetty ErrorHandler with a vague response

Mirror the behavior of RestApiServlet. Anytime an exception is
caught by Jetty format back just "Internal server error" after
logging the exception to the server's error log.

Change-Id: I3b1dfdea45b833b5ffd0cd1731d24ecf7cd75eb1

gerrit-pgm/BUCK

@@ -6,6 +6,7 @@ java_library2(
     '//gerrit-cache-h2:cache-h2',
     '//gerrit-common:server',
     '//gerrit-extension-api:api',
+    '//gerrit-gwtexpui:server',
     '//gerrit-httpd:httpd',
     '//gerrit-openid:openid',
     '//gerrit-server:common_rules',

gerrit-pgm/src/main/java/com/google/gerrit/pgm/http/jetty/HiddenErrorHandler.java

@@ -0,0 +1,79 @@
+// Copyright (C) 2013 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.pgm.http.jetty;
+
+import static javax.servlet.http.HttpServletResponse.SC_INTERNAL_SERVER_ERROR;
+
+import com.google.common.base.Charsets;
+import com.google.common.base.Strings;
+import com.google.gwtexpui.server.CacheHeaders;
+
+import org.eclipse.jetty.http.HttpHeaders;
+import org.eclipse.jetty.server.AbstractHttpConnection;
+import org.eclipse.jetty.server.Request;
+import org.eclipse.jetty.server.handler.ErrorHandler;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+
+import javax.servlet.ServletOutputStream;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+class HiddenErrorHandler extends ErrorHandler {
+  private static final Logger log = LoggerFactory.getLogger(HiddenErrorHandler.class);
+  private static final byte[] MSG = "Internal server error\n".getBytes(Charsets.ISO_8859_1);
+
+  public void handle(String target, Request baseRequest,
+      HttpServletRequest req, HttpServletResponse res) throws IOException {
+    AbstractHttpConnection.getCurrentConnection().getRequest().setHandled(true);
+    try {
+      log(req);
+    } finally {
+      replyGenericError(res);
+    }
+  }
+
+  private void replyGenericError(HttpServletResponse res) throws IOException {
+    if (!res.isCommitted()) {
+      res.reset();
+      res.setStatus(SC_INTERNAL_SERVER_ERROR);
+      res.setHeader(HttpHeaders.CONTENT_TYPE, "text/plain; charset=ISO-8859-1");
+      res.setContentLength(MSG.length);
+      try {
+        CacheHeaders.setNotCacheable(res);
+      } finally {
+        ServletOutputStream out = res.getOutputStream();
+        try {
+          out.write(MSG);
+        } finally {
+          out.close();
+        }
+      }
+    }
+  }
+
+  private static void log(HttpServletRequest req) {
+    Throwable err = (Throwable)req.getAttribute("javax.servlet.error.exception");
+    if (err != null) {
+      String uri = req.getRequestURI();
+      if (!Strings.isNullOrEmpty(req.getQueryString())) {
+        uri += "?" + req.getQueryString();
+      }
+      log.error(String.format("Error in %s %s", req.getMethod(), uri), err);
+    }
+  }
+}

gerrit-pgm/src/main/java/com/google/gerrit/pgm/http/jetty/JettyServer.java

@@ -332,6 +332,7 @@ public class JettyServer {
     // for Gerrit plug-ins to enable user-level sessions.
     //
     app.setSessionHandler(new SessionHandler());
+    app.setErrorHandler(new HiddenErrorHandler());
 
     // This is the path we are accessed by clients within our domain.
     //