Issue 5183 - Provide async interface for FileSystem

include/AdblockPlus/DefaultFileSystem.h

Index: include/AdblockPlus/DefaultFileSystem.h
===================================================================
--- a/include/AdblockPlus/DefaultFileSystem.h
+++ b/include/AdblockPlus/DefaultFileSystem.h
@@ -29,30 +29,51 @@
 namespace AdblockPlus
 {
   /**
    * `FileSystem` implementation that interacts directly with the operating
    * system's file system.
    * All paths are considered relative to the base path, or to the current
    * working directory if no base path is set (see `SetBasePath()`).
    */
-  class DefaultFileSystem : public FileSystem
+  class DefaultFileSystemSync : public FileSystem
   {
   public:
-    IOBuffer Read(const std::string& path) const;
-    void Write(const std::string& path, const IOBuffer& data);
+    IFileSystem::IOBuffer Read(const std::string& path) const;
+    void Write(const std::string& path, const IFileSystem::IOBuffer& data);
     void Move(const std::string& fromPath, const std::string& toPath);
     void Remove(const std::string& path);
-    StatResult Stat(const std::string& path) const;
+    IFileSystem::StatResult Stat(const std::string& path) const;
     std::string Resolve(const std::string& path) const;
 
     /**
      * Sets the base path, all paths are considered relative to it.
      * @param path Base path.
      */
     void SetBasePath(const std::string& path);
 
   protected:
     std::string basePath;
   };
+
+  class DefaultFileSystem : public IFileSystem
+  {
+  public:
+    explicit DefaultFileSystem(const FileSystemSyncPtr& syncImpl);
+    void Read(const std::string& path,
+              const ReadCallback& callback) const;
+    void Write(const std::string& path,
+               const IOBuffer& data,
+               const Callback& callback);
+    void Move(const std::string& fromPath,
+              const std::string& toPath,
+              const Callback& callback);
+    void Remove(const std::string& path, const Callback& callback);
+    void Stat(const std::string& path,
+              const StatCallback& callback) const;
+
+    std::string Resolve(const std::string& path) const;
+  private:
+    FileSystemSyncPtr syncImpl;
+  };
 }
 
 #endif