Drag&drop Shell Extension

The extension is installed by WinSCP installer by default (the portable WinSCP executable does not include the extension and it cannot be downloaded separately).

Newly installed extension is loaded only the next time you log in to Windows. So you may need to restart your machine or log off and log in again to load it.1

To check that the extension is loaded, run WinSCP and display Drag&drop page of Preferences window.

To tell WinSCP to use the extension, select Determine drop target by dragging a fake file checkbox. Note that unselecting it (or rather selecting Download files via temporary folder checkbox) does not uninstall the extension. It will be still loaded into memory and will be loaded every time the operating system starts up.

When the extension is enabled in WinSCP the only destination application you can drag files to is Windows File Explorer (this includes Desktop). Of course you can still drag files within WinSCP.

In addition, as the files are actually transferred directly to the target folder, not “dropped” on the target window, the Window File Explorer will not place them on the spot, where you have dropped them. Instead they will appear on automatically selected position.

Note that the extension is registered in the operating system (or rather Windows File Explorer) and thus it is loaded into memory even if you do not use WinSCP.

This chapter is for those who are curious why WinSCP needs shell extension to allow direct downloads using drag&drop.

Here is short explanation: Windows drag&drop mechanics does not allow source application of drag&drop operation to find out easily, where the files are dropped. It is up to target application (Windows File Explorer usually) to transfer files to destination. It is rather reasonable, because source application can hardly transfer files to all possible destinations. Keep in mind that you can drop files not only to a directory, but even to ZIP file (or any other archive), remote directory (via FTP, SFTP, SCP, …), trash, …

Obviously even Windows File Explorer (or any other target application, like WinZip) cannot download files from any possible source (particularly it does not know SFTP/SCP).

When the extension is not installed, WinSCP uses a trick to allow drag&drop downloads. It tells Windows File Explorer that the files are in temporary folder (from where Windows File Explorer knows how to get the files) and a moment before the Windows File Explorer starts to copy files from there, WinSCP downloads the files there.

To allow direct drag&drop downloads, the shell extension was developed. It misuses Windows File Explorer CopyHook’s. CopyHook is a COM object (DLL library) that is called by Windows File Explorer whenever directory (not file) is transferred within file system. When you drag anything from WinSCP, it creates empty dummy folder in temporary directory and pretends that you as user drag that directory. Once your drop it to Windows File Explorer, it calls the CopyHook’s (including the WinSCP shell extension), telling it what and where was dragged. This way WinSCP knows the actual destination. It cancels the drag&drop operation, so the dummy directory is not copied by Windows File Explorer and transfers your actual selection to now-known destination.

This on the other hand explains why with the extension you cannot drag files to any other application except for the Windows File Explorer. No other application would call the CopyHook.