Allow specification of appbase via system property.

This allows one to bootstrap a Getdown install with no files at all. You don't
get a very sexy UI during the first install, but you can make something
non-horrible with a background color and a small window.

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

@@ -261,7 +261,7 @@ public class Application
         try {
             return createResource(CONFIG_FILE, false);
         } catch (Exception e) {
-            throw new RuntimeException("Invalid appbase '" + _vappbase + "'.");
+            throw new RuntimeException("Invalid appbase '" + _vappbase + "'.", e);
         }
     }
 
@@ -472,10 +472,10 @@ public class Application
     }
 
     /**
-     * Instructs the application to parse its <code>getdown.txt</code> configuration and prepare
-     * itself for operation. The application base URL will be parsed first so that if there are
-     * errors discovered later, the caller can use the application base to download a new
-     * <code>config.txt</code> file and try again.
+     * Instructs the application to parse its {@code getdown.txt} configuration and prepare itself
+     * for operation. The application base URL will be parsed first so that if there are errors
+     * discovered later, the caller can use the application base to download a new {@code
+     * getdown.txt} file and try again.
      *
      * @return a configured UpdateInterface instance that will be used to configure the update UI.
      *
@@ -485,26 +485,36 @@ public class Application
     public UpdateInterface init (boolean checkPlatform)
         throws IOException
     {
-        // parse our configuration file
         Map<String,Object> cdata = null;
+        File config = _config;
         try {
+            // if we have a configuration file, read the data from it
+            if (config.exists()) {
                 cdata = ConfigUtil.parseConfig(_config, checkPlatform);
-        } catch (FileNotFoundException fnfe) {
-            // thanks to funny windows bullshit, we have to do this backup file fiddling in case we
-            // got screwed while updating our very critical getdown config file
-            File cbackup = getLocalPath(CONFIG_FILE + "_old");
-            if (cbackup.exists()) {
-                cdata = ConfigUtil.parseConfig(cbackup, checkPlatform);
-            } else {
-                throw fnfe;
             }
+            // otherwise, try reading data from our backup config file; thanks to funny windows
+            // bullshit, we have to do this backup file fiddling in case we got screwed while
+            // updating getdown.txt during normal operation
+            else if ((config = getLocalPath(CONFIG_FILE + "_old")).exists()) {
+                cdata = ConfigUtil.parseConfig(config, checkPlatform);
+            }
+        } catch (Exception e) {
+            log.warning("Failure reading config file", "file", config, e);
+        }
+        // if we failed to read our config file, check for an appbase specified via a system
+        // property; we can use that to bootstrap ourselves back into operation
+        if (cdata == null) {
+            log.info("Found no getdown.txt file. Falling back to appbase system prop",
+                     "appbase", SysProps.appBase());
+            cdata = new HashMap<String,Object>();
+            cdata.put("appbase", SysProps.appBase());
         }
 
         // first determine our application base, this way if anything goes wrong later in the
         // process, our caller can use the appbase to download a new configuration file
         _appbase = (String)cdata.get("appbase");
         if (_appbase == null) {
-            throw new IOException("m.missing_appbase");
+            throw new RuntimeException("m.missing_appbase");
         }
         // make sure there's a trailing slash
         if (!_appbase.endsWith("/")) {
@@ -524,11 +534,7 @@ public class Application
 
         // if we are a versioned deployment, create a versioned appbase
         try {
-            if (_version < 0) {
-                _vappbase = new URL(_appbase);
-            } else {
-                _vappbase = createVAppBase(_version);
-            }
+            _vappbase = (_version < 0) ? new URL(_appbase) : createVAppBase(_version);
         } catch (MalformedURLException mue) {
             String err = MessageUtil.tcompose("m.invalid_appbase", _appbase);
             throw (IOException) new IOException(err).initCause(mue);

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

@@ -23,6 +23,12 @@ public class SysProps
         return System.getProperty("appid");
     }
 
+    /** Configures the appbase (in lieu of providing a skeleton getdown.txt, and as a last resort
+     * fallback). Usage: {@code -Dappbase=someurl}. */
+    public static String appBase () {
+        return System.getProperty("appbase");
+    }
+
     /** If true, disables redirection of logging into {@code launcher.log}.
      * Usage: {@code -Dno_log_redir}. */
     public static boolean noLogRedir () {