Load Google prettify JavaScript into client

We now load the Google prettify JavaScript code into the browser as
part of the Gerrit bootstrap.  The script is created with a defer
tag, so it can load in parallel with other page resources.  We also
use a custom servlet to send all of the JavaScript files combined
as one stream, with a very long cache time of 1 year.  This should
permit browsers to only load the highlighting library once very
few months, as it is somewhat large (~30 KiB).

Bug: GERRIT-228
Signed-off-by: Shawn O. Pearce <sop@google.com>

src/main/java/com/google/gerrit/server/PrettifyServlet.java

@@ -0,0 +1,87 @@
+// Copyright (C) 2009 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.server;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+
+import javax.servlet.ServletConfig;
+import javax.servlet.ServletException;
+import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+public class PrettifyServlet extends HttpServlet {
+  private static final String VERSION = "20090521";
+
+  private byte[] content;
+
+  @Override
+  public void init(ServletConfig config) throws ServletException {
+    super.init(config);
+
+    final String myDir = "/gerrit/prettify" + VERSION + "/";
+    final ByteArrayOutputStream buffer = new ByteArrayOutputStream();
+    load(buffer, myDir + "prettify.js");
+    for (Object p : getServletContext().getResourcePaths(myDir)) {
+      String name = (String) p;
+      if (name.startsWith(myDir + "lang-") && name.endsWith(".js")) {
+        load(buffer, name);
+      }
+    }
+    content = buffer.toByteArray();
+  }
+
+  private void load(final OutputStream buffer, final String path) {
+    final InputStream in = getServletContext().getResourceAsStream(path);
+    if (in != null) {
+      try {
+        final byte[] tmp = new byte[4096];
+        int cnt;
+        while ((cnt = in.read(tmp)) > 0) {
+          buffer.write(tmp, 0, cnt);
+        }
+        buffer.write(';');
+        buffer.write('\n');
+        in.close();
+      } catch (IOException e) {
+        getServletContext().log("Cannot read " + path, e);
+      }
+    }
+  }
+
+  @Override
+  protected void doGet(final HttpServletRequest req,
+      final HttpServletResponse rsp) throws IOException {
+    final String want = req.getPathInfo();
+    if (want.equals("/" + VERSION + ".js")) {
+      final long now = System.currentTimeMillis();
+      rsp.setHeader("Cache-Control", "max-age=31536000,public");
+      rsp.setDateHeader("Expires", now + 31536000000L);
+      rsp.setDateHeader("Date", now);
+      rsp.setContentType("application/x-javascript");
+      rsp.setContentLength(content.length);
+      rsp.getOutputStream().write(content);
+    } else {
+      rsp.setHeader("Expires", "Fri, 01 Jan 1980 00:00:00 GMT");
+      rsp.setHeader("Pragma", "no-cache");
+      rsp.setHeader("Cache-Control", "no-cache, must-revalidate");
+      rsp.setDateHeader("Date", System.currentTimeMillis());
+      rsp.sendError(HttpServletResponse.SC_NOT_FOUND);
+    }
+  }
+}