Use server side permutation selection

By selecting the GWT permutation on the server side, we can avoid
an HTTP request for the gerrit.nocache.js file, avoid downloading
5100+ bytes worth of uncompressed JavaScript, and instead can add
only about 519 bytes to our compressed host page.

Startup feels faster in most browsers, due to the iframe being
able to be prepared more quickly, and the stylesheet loading in
parallel to other page assets like the header/footer.

Change-Id: Ia91504706b910d3ba6b7b92396c4f0ce89ca1968
Signed-off-by: Shawn O. Pearce <sop@google.com>

gerrit-gwtui/src/main/java/com/google/gerrit/GerritGwtUI.gwt.xml

@@ -20,6 +20,7 @@
   <inherits name='com.google.gwtexpui.clippy.Clippy'/>
   <inherits name='com.google.gwtexpui.css.CSS'/>
   <inherits name='com.google.gwtexpui.globalkey.GlobalKey'/>
+  <inherits name='com.google.gwtexpui.linker.ServerPlannedIFrameLinker'/>
   <inherits name='com.google.gwtexpui.progress.Progress'/>
   <inherits name='com.google.gwtexpui.safehtml.SafeHtml'/>
   <inherits name='com.google.gwtexpui.safehtml.PrettyFormatter'/>

gerrit-httpd/src/main/java/com/google/gerrit/httpd/raw/HostPageServlet.java

@@ -21,6 +21,8 @@ import com.google.gerrit.server.CurrentUser;
 import com.google.gerrit.server.IdentifiedUser;
 import com.google.gerrit.server.config.SitePaths;
 import com.google.gwt.user.server.rpc.RPCServletUtils;
+import com.google.gwtexpui.linker.server.Permutation;
+import com.google.gwtexpui.linker.server.PermutationSelector;
 import com.google.gwtjsonrpc.server.JsonServlet;
 import com.google.inject.Inject;
 import com.google.inject.Provider;
@@ -40,8 +42,11 @@ import java.io.InputStream;
 import java.io.OutputStream;
 import java.io.StringWriter;
 import java.security.MessageDigest;
+import java.util.HashMap;
+import java.util.Map;
 
 import javax.servlet.ServletContext;
+import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
@@ -59,12 +64,14 @@ public class HostPageServlet extends HttpServlet {
   private final GerritConfig config;
   private final SitePaths site;
   private final Document template;
+  private final String noCacheName;
+  private final PermutationSelector selector;
   private volatile Page page;
 
   @Inject
   HostPageServlet(final Provider<CurrentUser> cu, final SitePaths sp,
       final GerritConfig gc, final ServletContext servletContext)
-      throws IOException {
+      throws IOException, ServletException {
     currentUser = cu;
     config = gc;
     site = sp;
@@ -75,26 +82,23 @@ public class HostPageServlet extends HttpServlet {
       throw new FileNotFoundException("No " + pageName + " in webapp");
     }
 
-    if (!IS_DEV) {
+    if (HtmlDomUtil.find(template, "gerrit_module") == null) {
+      throw new ServletException("No gerrit_module in " + pageName);
+    }
+    if (HtmlDomUtil.find(template, HPD_ID) == null) {
+      throw new ServletException("No " + HPD_ID + " in " + pageName);
+    }
+
+    final String src = "gerrit/gerrit.nocache.js";
+    selector = new PermutationSelector("gerrit");
+    if (IS_DEV) {
+      noCacheName = src;
+    } else {
       final Element devmode = HtmlDomUtil.find(template, "gerrit_gwtdevmode");
       if (devmode != null) {
         devmode.getParentNode().removeChild(devmode);
       }
-    }
 
-    fixModuleReference(template, servletContext);
-    page = new Page();
-  }
-
-  private void fixModuleReference(final Document hostDoc,
-      final ServletContext servletContext) throws IOException {
-    final Element scriptNode = HtmlDomUtil.find(hostDoc, "gerrit_module");
-    if (scriptNode == null) {
-      throw new IOException("No gerrit_module to rewrite in host document");
-    }
-
-    String src = "gerrit/gerrit.nocache.js";
-    if (!IS_DEV) {
       InputStream in = servletContext.getResourceAsStream("/" + src);
       if (in == null) {
         throw new IOException("No " + src + " in webapp root");
@@ -114,23 +118,18 @@ public class HostPageServlet extends HttpServlet {
       } catch (IOException e) {
         throw new IOException("Failed reading " + src, e);
       }
-
+      final String id = ObjectId.fromRaw(md.digest()).name();
-      src += "?content=" + ObjectId.fromRaw(md.digest()).name();
+      noCacheName = src + "?content=" + id;
+      selector.init(servletContext);
     }
-    scriptNode.setAttribute("src", src);
+
-    asScript(scriptNode);
+    page = new Page();
   }
 
   private void json(final Object data, final StringWriter w) {
     JsonServlet.defaultGsonBuilder().create().toJson(data, w);
   }
 
-  private static void asScript(final Element scriptNode) {
-    scriptNode.removeAttribute("id");
-    scriptNode.setAttribute("type", "text/javascript");
-    scriptNode.setAttribute("language", "javascript");
-  }
-
   private Page get() {
     Page p = page;
     if (p.isStale()) {
@@ -150,7 +149,7 @@ public class HostPageServlet extends HttpServlet {
   @Override
   protected void doGet(final HttpServletRequest req,
       final HttpServletResponse rsp) throws IOException {
-    final Page page = get();
+    final Page.Content page = get().get(selector.select(req));
     final byte[] raw;
 
     final CurrentUser user = currentUser.get();
@@ -220,11 +219,7 @@ public class HostPageServlet extends HttpServlet {
     private final FileInfo css;
     private final FileInfo header;
     private final FileInfo footer;
-
+    private final Map<Permutation, Content> permutations;
-    final byte[] part1;
-    final byte[] part2;
-    final byte[] full;
-    final byte[] full_gz;
 
     Page() throws IOException {
       Document hostDoc = HtmlDomUtil.clone(template);
@@ -242,28 +237,62 @@ public class HostPageServlet extends HttpServlet {
       w.write(";");
 
       final Element data = HtmlDomUtil.find(hostDoc, HPD_ID);
-      if (data == null) {
-        throw new IOException("No " + HPD_ID + " in host page HTML");
-      }
       asScript(data);
       data.appendChild(hostDoc.createTextNode(w.toString()));
       data.appendChild(hostDoc.createComment(HPD_ID));
 
-      final String raw = HtmlDomUtil.toString(hostDoc);
+      permutations = new HashMap<Permutation, Content>();
-      final int p = raw.indexOf("<!--" + HPD_ID);
+      for (Permutation p : selector.getPermutations()) {
-      if (p < 0) {
+        final Document d = HtmlDomUtil.clone(hostDoc);
-        throw new IOException("No tag in transformed host page HTML");
+        Element nocache = HtmlDomUtil.find(d, "gerrit_module");
+        nocache.getParentNode().removeChild(nocache);
+        p.inject(d);
+        permutations.put(p, new Content(d));
       }
-      part1 = raw.substring(0, p).getBytes("UTF-8");
+
-      part2 = raw.substring(raw.indexOf('>', p) + 1).getBytes("UTF-8");
+      Element nocache = HtmlDomUtil.find(hostDoc, "gerrit_module");
-      full = concat(part1, part2, new byte[0]);
+      asScript(nocache);
-      full_gz = HtmlDomUtil.compress(full);
+      nocache.setAttribute("src", noCacheName);
+      permutations.put(null, new Content(hostDoc));
+    }
+
+    Content get(Permutation p) {
+      Content c = permutations.get(p);
+      if (c == null) {
+        c = permutations.get(null);
+      }
+      return c;
     }
 
     boolean isStale() {
       return css.isStale() || header.isStale() || footer.isStale();
     }
 
+    private void asScript(final Element scriptNode) {
+      scriptNode.removeAttribute("id");
+      scriptNode.setAttribute("type", "text/javascript");
+      scriptNode.setAttribute("language", "javascript");
+    }
+
+    class Content {
+      final byte[] part1;
+      final byte[] part2;
+      final byte[] full;
+      final byte[] full_gz;
+
+      Content(Document hostDoc) throws IOException {
+        final String raw = HtmlDomUtil.toString(hostDoc);
+        final int p = raw.indexOf("<!--" + HPD_ID);
+        if (p < 0) {
+          throw new IOException("No tag in transformed host page HTML");
+        }
+        part1 = raw.substring(0, p).getBytes("UTF-8");
+        part2 = raw.substring(raw.indexOf('>', p) + 1).getBytes("UTF-8");
+        full = concat(part1, part2, new byte[0]);
+        full_gz = HtmlDomUtil.compress(full);
+      }
+    }
+
     private FileInfo injectCssFile(final Document hostDoc, final String id,
         final File src) throws IOException {
       final FileInfo info = new FileInfo(src);

gerrit-httpd/src/main/resources/com/google/gerrit/httpd/raw/HostPage.html

@@ -31,7 +31,6 @@
       })();
     </script>
     <script id="gerrit_hostpagedata"></script>
-    <script id="gerrit_module"></script>
     <style  id="gerrit_sitecss" type="text/css"></style>
     <link rel="icon" type="image/gif" href="favicon.ico" />
   </head>
@@ -50,5 +49,6 @@
       <div id="gerrit_btmmenu" style="clear: both;"></div>
     </div>
     <iframe src="javascript:''" id="__gwt_historyFrame" tabIndex='-1' style="position:absolute;width:0;height:0;border:0"></iframe>
+    <script id="gerrit_module"></script>
   </body>
 </html>