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
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-#ifndef ADBLOCK_PLUS_FILE_SYSTEM_H
-#define ADBLOCK_PLUS_FILE_SYSTEM_H
+#ifndef ADBLOCK_PLUS_IFILE_SYSTEM_H
+#define ADBLOCK_PLUS_IFILE_SYSTEM_H
 
 #include <istream>
 #include <stdint.h>
 #include <string>
 #include <memory>
+#include <vector>
 
 namespace AdblockPlus
 {
   /**
    * File system interface.
    */
-  class FileSystem
+  class IFileSystem
   {
   public:
     /**
      * Result of a stat operation, i.e.\ information about a file.
      */
     struct StatResult
     {
       StatResult()
       {
         exists = false;
@@ skipping 16 matching lines @@
        * File is a regular file.
        */
       bool isFile;
 
       /**
        * POSIX time of the last modification.
        */
       int64_t lastModified;
     };
 
-    virtual ~FileSystem() {}
+    virtual ~IFileSystem() {}
+
+    /**
+     * 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.

+                               const std::string&)> ReadCallback;
 
     /**
      * Reads from a file.
      * @param path File path.
-     * @return Input stream with the file's contents.
+     * @param callback The function called on completion with the input data.
      */
-    virtual std::shared_ptr<std::istream>
-      Read(const std::string& path) const = 0;
+    virtual void Read(const std::string& path,
+                      const ReadCallback& callback) const = 0;
 
     /**
      * Writes to a file.
      * @param path File path.
-     * @param data Input stream with the data to write.
+     * @param data The data to write.
+     * @param callback The function called on completion.
      */
     virtual void Write(const std::string& path,
-                       std::istream& data) = 0;
+                       const std::vector<char>& 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) = 0;
+    virtual void Move(const std::string& fromPath, const std::string& toPath,
+                      const Callback& callback) = 0;
 
     /**
      * Removes a file.
      * @param path File path.
+     * @param callback The function called on completion.
      */
-    virtual void Remove(const std::string& path) = 0;
+    virtual void Remove(const std::string& path, const Callback& callback) = 0;
+
+    /**
+     * Callback type for the asynchronous Stat call.
+     * @param the StatResult data.
+     * @param an error string. Empty if no error.
+     */
+    typedef std::function<void(const StatResult&, const std::string&)> StatCallback;
 
     /**
      * Retrieves information about a file.
      * @param path File path.
-     * @return File information.
+     * @param callback The function called on completion.
      */
-    virtual StatResult Stat(const std::string& path) const = 0;
+    virtual void Stat(const std::string& path,
+                      const StatCallback& callback) const = 0;
 
     /**
      * Returns the absolute path to a file.
      * @param path File path (can be relative or absolute).
      * @return Absolute file path.
      */
     virtual std::string Resolve(const std::string& path) const = 0;
   };
 
   /**
-   * Shared smart pointer to a `FileSystem` instance.
+   * Shared smart pointer to a `IFileSystem` instance.
    */
-  typedef std::shared_ptr<FileSystem> FileSystemPtr;
+  typedef std::shared_ptr<IFileSystem> FileSystemPtr;
 }
 
 #endif