Saturday, October 9, 2010

Windows 7 has directory symlinks! And they are a great way to work around Dropbox limitations!

Dropbox is moderately awesome. One of the remarkably rare pieces of software that "just works" (so far). Except they haven't implemented the sync any folder feature (vote here!) despite receiving 60k votes for it over an 11 month period :( This causes horribly mundane and annoying problems like:
  • I want to use P:\Dropbox as my sync folder; ok, works great!
  • I have a shared folder for Starcraft 2 replays so I get replays under P:\Dropbox\My Dropbox\SC2-Replay. 
  • Starcraft 2 doesn't look there; in order to have these replays show up for selection in the replays list I need to sync only the SC2-Replay directory into a subdirectory of the directory Starcraft 2 looks at 
    • That is, I want C:\Users\UserName\Documents\StarCraft II\Accounts\########\1-S2-1-######\Replays to sync with the same thing as P:\Dropbox\My Dropbox\SC2-Replay
I could just put the entire Dropbox folder under Starcraft 2 but that really isn't ideal. In XP we'd have a problem; NTFS only had junction points (ref) and it wasn't as easy as you might hope to create them. Luckily in Windows 7 (and Vista) we finally get directory symlinks (ref)! Always nice to learn something useful while trying to accomplish something frivolous like making watching game replays easier.

So, having found out directory symlinks are now available I figured I'd find out how to create one. The first way I found was perhaps not as easy as I'd hoped:

BOOLEAN WINAPI CreateSymbolicLink(
  __in  LPTSTR lpSymlinkFileName,
  __in  LPTSTR lpTargetFileName,
  __in  DWORD dwFlags

Luckily it turns out that Windows 7 also provide mklink.exe (Vista has it too; although new to me mklink.exe is old news to the world) to handle all your command prompt NTFS linking needs. You can even create directory junctions (ref) with it if so inclined! Plus Windows Explorer now handles deletion of a directory junction graciously - the files don't get deleted if you delete the junction directory expecting the original/other access point in the file system to stick around.

The mklink.exe arguments are nice and simple:

>mklink /?
Creates a symbolic link.

MKLINK [[/D] | [/H] | [/J]] Link Target

        /D      Creates a directory symbolic link.  Default is a file
                symbolic link.
        /H      Creates a hard link instead of a symbolic link.
        /J      Creates a Directory Junction.
        Link    specifies the new symbolic link name.
        Target  specifies the path (relative or absolute) that the new link
                refers to.

Somewhat curiously (at least to me) creating a directory junction to link up my Dropbox replay to the Starcraft 2 directory tree did not require elevated permissions but creating a directory symlink required me to run cmd.exe as admin. Apparently this is by design but it seems a bit odd; I would have thought a junction was a bigger deal than a symlink. Anyway, once running as admin the link creates as easily as one could hope:

C:\Users\Imaginary\Documents\StarCraft II\Accounts\########\1-S2-1-######\Replays\Multiplayer>mklink /D DropboxSymLink "P:\Dropbox\My Dropbox\SC2-Replay"
symbolic link created for DropboxSymLink <<===>> P:\Dropbox\My Dropbox\SC2-Replay

And now I can see the replays people drop into our shared Dropbox folder from within Starcraft 2; yay!

It may be a bit manual but until that Dropbox gets that external folders feature this is going to be very handy; I can have different parts of my Dropbox show up scattered all over my filesystem now!


antred said...

I know this 3 years after the fact, but I'm still amazed that it took Microsoft only 4 decades to catch up to the rest of the world! :)

john said...

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