Issue 5183 - Provide async interface for FileSystem

include/AdblockPlus/IFileSystem.h

 /*
  * 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 50 matching lines @@
       bool isFile;
 
       /**
        * POSIX time of the last modification.
        */
       int64_t lastModified;
     };
 
     virtual ~IFileSystem() {}
 
+    /** Type for the buffer used for IO */
+    typedef std::vector<uint8_t> IOBuffer;
+
     /**
      * 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(std::vector<char>&&,

[sergei, 2017/07/06 14:14:05]

Since it's for bytes, I would rather prefer an unsigned type like uint8_t or
`unsigned char` than char which takes values from -128 to 127.
BTW, what about having a typedef for the buffer?

[hub, 2017/07/06 14:33:31]

But iostream and making it harder. If I use std::vector<unsigned char> I need to
use basic_istream<unsigned char> which requires to specialize a
std::char_traits<> for it, etc. Unless I cast, etc.

I thought this was the best way to keep it simple.

I can typedef the buffer though.

[sergei, 2017/07/06 14:53:33]

I think we should simply cast to `const char*` or `char*` when it's needed, e.g.
if we work with C++ streams in the default implementation of the sync interface
then we can cast `static_cast<const std::ostream::char_type*>(data.data());` to
pass it to std::ostream::write where data is the vector of bytes and similar for
v8 conversions if it's necessary there.

[hub, 2017/07/06 21:24:30]

fair enough.

+    typedef std::function<void(IOBuffer&&,
                                const std::string&)> ReadCallback;
 
     /**
      * Reads from a file.
      * @param path File path.
      * @param callback The function called on completion with the input data.
      */
     virtual void Read(const std::string& path,
                       const ReadCallback& callback) const = 0;
 
     /**
      * Writes to a file.
      * @param path File path.
      * @param data The data to write.
      * @param callback The function called on completion.
      */
     virtual void Write(const std::string& path,
-                       const std::vector<char>& data,
+                       const IOBuffer& data,
                        const Callback& callback) = 0;
 
     /**
      * Moves a file (i.e.\ renames it).
      * @param fromPath Current path to the file.
      * @param toPath New path to the file.
      * @param callback The function called on completion.
      */
     virtual void Move(const std::string& fromPath, const std::string& toPath,
                       const Callback& callback) = 0;
@@ skipping 28 matching lines @@
     virtual std::string Resolve(const std::string& path) const = 0;
   };
 
   /**
    * Shared smart pointer to a `IFileSystem` instance.
    */
   typedef std::shared_ptr<IFileSystem> FileSystemPtr;
 }
 
 #endif