Added override_appbase system property.

This can be used to completely override the appbase via the installer in
situations where you want to build a deployment once, but then potentially
serve it from some other webserver.

src/main/java/com/threerings/getdown/data/Application.java

@@ -537,14 +537,15 @@ public class Application
         if (_appbase == null) {
             throw new RuntimeException("m.missing_appbase");
         }
+
+        // check if we're overriding the domain in the appbase
+        _appbase = overrideAppbase(_appbase);
+
         // make sure there's a trailing slash
         if (!_appbase.endsWith("/")) {
             _appbase = _appbase + "/";
         }
 
-        // check if we're overriding the domain in the appbase
-        _appbase = replaceDomain(_appbase);
-
         // extract our version information
         String vstr = (String)cdata.get("version");
         if (vstr != null) _version = parseLong(vstr, "m.invalid_version");
@@ -560,7 +561,11 @@ public class Application
         // check for a latest config URL
         String latest = (String)cdata.get("latest");
         if (latest != null) {
+            if (latest.startsWith(_appbase)) {
+                latest = _appbase + latest.substring(_appbase.length());
+            } else {
                 latest = replaceDomain(latest);
+            }
             try {
                 _latest = new URL(latest);
             } catch (MalformedURLException mue) {
@@ -1736,6 +1741,18 @@ public class Application
         return cookie.toString();
     }
 
+    /**
+     * Applies {@code appbase_override} or {@code appbase_domain} if they are set.
+     */
+    protected String overrideAppbase (String appbase) {
+        String appbaseOverride = SysProps.appbaseOverride();
+        if (appbaseOverride != null) {
+            return appbaseOverride;
+        } else {
+            return replaceDomain(appbase);
+        }
+    }
+
     /**
      * If appbase_domain property is set, replace the domain on the provided string.
      */

src/main/java/com/threerings/getdown/data/SysProps.java

@@ -27,7 +27,7 @@ public class SysProps
     }
 
     /** Configures the appbase (in lieu of providing a skeleton getdown.txt, and as a last resort
-      * fallback). Usage: {@code -Dappbase=someurl}. */
+      * fallback). Usage: {@code -Dappbase=URL}. */
     public static String appBase () {
         return System.getProperty("appbase");
     }
@@ -43,6 +43,11 @@ public class SysProps
         return System.getProperty("appbase_domain");
     }
 
+    /** Overrides enter {@code appbase}. Usage: {@code -Dappbase_override=URL}. */
+    public static String appbaseOverride () {
+        return System.getProperty("appbase_override");
+    }
+
     /** If true, Getdown installs the app without ever bringing up a UI, except in the event of an
       * error. NOTE: it does not launch the app. See {@link #launchInSilent}.
       * Usage: {@code -Dsilent}. */