Reload UI if code split fails to download

If the server was upgraded, a code segment might not download
as its no longer available through the web application context.
Catch this failure and automatically reload the web UI, trying to
go back to the location the user requested.

Bug: issue 486
Change-Id: Ie235c9d30b7335fd7414b3ef082ec459ed794627
Signed-off-by: Shawn O. Pearce <sop@google.com>

gerrit-gwtui/src/main/java/com/google/gerrit/client/Dispatcher.java

diff --git a/gerrit-gwtui/src/main/java/com/google/gerrit/client/Dispatcher.java b/gerrit-gwtui/src/main/java/com/google/gerrit/client/Dispatcher.java
index a9d5825..7db92ad 100644
--- a/gerrit-gwtui/src/main/java/com/google/gerrit/client/Dispatcher.java
+++ b/gerrit-gwtui/src/main/java/com/google/gerrit/client/Dispatcher.java
@@ -83,10 +83,21 @@
     return "admin,project," + n.toString() + "," + tab;
   }
 
-  void display(final String token) {
+  static final String RELOAD_UI = "reload-ui,";
+  private static boolean wasStartedByReloadUI;
+
+  void display(String token) {
     assert token != null;
     try {
-      select(token);
+      try {
+        if (token.startsWith(RELOAD_UI)) {
+          wasStartedByReloadUI = true;
+          token = skip(RELOAD_UI, token);
+        }
+        select(token);
+      } finally {
+        wasStartedByReloadUI = false;
+      }
     } catch (RuntimeException err) {
       GWT.log("Error parsing history token: " + token, err);
       Gerrit.display(token, new NotFoundScreen());
@@ -217,8 +228,8 @@
     return new NotFoundScreen();
   }
 
-  private static void publish(final String token) {
-    new RunAsyncCallback() {
+  private static void publish(String token) {
+    new AsyncSplit(token) {
       public void onSuccess() {
         Gerrit.display(token, select());
       }
@@ -229,16 +240,12 @@
           return new PublishCommentScreen(PatchSet.Id.parse(skip(p, token)));
         return new NotFoundScreen();
       }
-
-      public void onFailure(Throwable reason) {
-        new ErrorDialog(reason).center();
-      }
     }.onSuccess();
   }
 
-  public static void patch(final String token, final Patch.Key id,
+  public static void patch(String token, final Patch.Key id,
       final int patchIndex, final PatchTable patchTable) {
-    GWT.runAsync(new RunAsyncCallback() {
+    GWT.runAsync(new AsyncSplit(token) {
       public void onSuccess() {
         Gerrit.display(token, select());
       }
@@ -266,15 +273,11 @@
 
         return new NotFoundScreen();
       }
-
-      public void onFailure(Throwable reason) {
-        new ErrorDialog(reason).center();
-      }
     });
   }
 
-  private static void settings(final String token) {
-    GWT.runAsync(new RunAsyncCallback() {
+  private static void settings(String token) {
+    GWT.runAsync(new AsyncSplit(token) {
       public void onSuccess() {
         Gerrit.display(token, select());
       }
@@ -328,15 +331,11 @@
 
         return new AccountSettings(token);
       }
-
-      public void onFailure(Throwable reason) {
-        new ErrorDialog(reason).center();
-      }
     });
   }
 
-  private static void admin(final String token) {
-    GWT.runAsync(new RunAsyncCallback() {
+  private static void admin(String token) {
+    GWT.runAsync(new AsyncSplit(token) {
       public void onSuccess() {
         Gerrit.display(token, select());
       }
@@ -366,14 +365,33 @@
 
         return new NotFoundScreen();
       }
-
-      public void onFailure(Throwable reason) {
-        new ErrorDialog(reason).center();
-      }
     });
   }
 
   private static String skip(final String prefix, final String in) {
     return in.substring(prefix.length());
   }
+
+  private static abstract class AsyncSplit implements RunAsyncCallback {
+    private final boolean isReloadUi;
+    protected final String token;
+
+    protected AsyncSplit(String token) {
+      this.isReloadUi = wasStartedByReloadUI;
+      this.token = token;
+    }
+
+    public final void onFailure(Throwable reason) {
+      if (!isReloadUi
+          && "HTTP download failed with status 404".equals(reason.getMessage())) {
+        // The server was upgraded since we last download the main script,
+        // so the pointers to the splits aren't valid anymore.  Force the
+        // page to reload itself and pick up the new code.
+        //
+        Gerrit.upgradeUI(token);
+      } else {
+        new ErrorDialog(reason).center();
+      }
+    }
+  }
 }

gerrit-gwtui/src/main/java/com/google/gerrit/client/Gerrit.java

diff --git a/gerrit-gwtui/src/main/java/com/google/gerrit/client/Gerrit.java b/gerrit-gwtui/src/main/java/com/google/gerrit/client/Gerrit.java
index 707c89f..d6a4995 100644
--- a/gerrit-gwtui/src/main/java/com/google/gerrit/client/Gerrit.java
+++ b/gerrit-gwtui/src/main/java/com/google/gerrit/client/Gerrit.java
@@ -84,6 +84,11 @@
     JsonUtil.bind(SYSTEM_SVC, "rpc/SystemInfoService");
   }
 
+  static void upgradeUI(String token) {
+    History.newItem(Dispatcher.RELOAD_UI + token, false);
+    Window.Location.reload();
+  }
+
   /**
    * Load the screen at the given location, displaying when ready.
    * <p>