Issue 5279 - Fix broken I/O in non-Firefox applications

lib/io.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2017 eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 227 matching lines @@
 
 let {application} = require("info");
 if (application != "firefox" && application != "fennec2")
 {
   // Currently, only Firefox has a working WebExtensions implementation, other
   // applications should just use the fallback.
   exports.IO = fallback;
 }
 else
 {
-  for (let name of [
-    "readFromFile", "copyFile", "renameFile", "removeFile", "statFile"

[Felix Dahlke, 2017/05/29 12:22:30]

We could avoid duplication here by iterating over the own properties in
fallback, just skipping over writeToFile.

[Wladimir Palant, 2017/05/29 12:41:23]

Done.

-  ])
-  {
-    // For missing files, fall back to legacy I/O for all methods except

[Felix Dahlke, 2017/05/29 12:22:30]

Nit: I think that comment should move in front of the `for` above, since the
logic starts there.

[Wladimir Palant, 2017/05/29 12:41:23]

Done.

-    // writeToFile()
+  // Add fallbacks to IO methods - fall back to legacy I/O if file wasn't found.
+  for (let name of Object.getOwnPropertyNames(exports.IO))
+  {
+    // No fallback for writeToFile method, new data should always be stored to
+    // new storage only.
+    if (name == "writeToFile")
+      continue;
+
     let method = exports.IO[name];
     let fallbackMethod = fallback[name];
     exports.IO[name] = (...args) =>
     {
       return method(...args).catch(error =>
       {
         if (error == "NoSuchFile")
           return fallbackMethod(...args);
         throw error;
       });
     };
   }
 }