Issue 6477 - separate done and error callbacks in IFileSystem::Read

include/AdblockPlus/IFileSystem.h

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present 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 51 matching lines @@
 
     /**
      * Default callback type for asynchronous filesystem calls.
      * @param An error string. Empty is success.
      */
     typedef std::function<void(const std::string&)> Callback;
 
     /**
      * Callback type for the asynchronous Read call.
      * @param Output char array with file content.
-     * @param An error string. Empty if success.
      */
-    typedef std::function<void(IOBuffer&&,
-                               const std::string&)> ReadCallback;
+    typedef std::function<void(IOBuffer&&)> ReadCallback;
 
     /**
      * Reads from a file.
      * @param fileName File name.
-     * @param callback The function called on completion with the input data.
+     * @param doneCallback The function called on completion with the input
+     *   data. If this function throws then the implementation should call
+     *   `errorCallback`.
+     * @param errorCallback The function called if an error occured.
      */
     virtual void Read(const std::string& fileName,
-                      const ReadCallback& callback) const = 0;
+                      const ReadCallback& doneCallback,
+                      const Callback& errorCallback) const = 0;
 
     /**
      * Writes to a file.
      * @param fileName File name.
      * @param data The data to write.
      * @param callback The function called on completion.
      */
     virtual void Write(const std::string& fileName,
                        const IOBuffer& data,
                        const Callback& callback) = 0;
@@ skipping 30 matching lines @@
                       const StatCallback& callback) const = 0;
   };
 
   /**
    * Unique smart pointer to to a `IFileSystem` instance.
    */
   typedef std::unique_ptr<IFileSystem> FileSystemPtr;
 }
 
 #endif