Copying a symlink does not preserve its type

[oliversalzburg]

• Operating System: Windows 10
• Node.js version: 8.11.1
• fs-extra version: 7.0.0

On Windows, when you attempt to copy a source, which is a symlink, fs-extra will always attempt to create a file symlink, regardless of what type of symlink the source is. This is an issue, as the result is unexpected and invalid.

Consider a source that is a junction (the most common type of link you're going to encounter on Windows). fs-extra will just invoke .symlink() without specifying a type, which will create a file symlink to the junction. The user will not be able to follow that link, because the junction isn't a file.

While you can work around the issue by passing dereference:true, I believe an attempt should be made to detect the type of link and then create a new link of the appropriate type.

[RyanZim]

Agreed this should be fixed. @oliversalzburg are you up to submitting a PR fixing it? (copySync probably has this problem as well) Please base any PRs against the v8-dev branch.

[oliversalzburg]

Yeah, I'd be happy to do it, but hit a roadblock right away. I don't see a clear way to make that distinction and I assume that's the reason why it hasn't be fixed already. Let's see if someone can give the right hint.

[oliversalzburg]

I didn't find a way through NodeJS to detect the difference and I also didn't find any existing work out there regarding this matter.

So I wrote https://github.com/oliversalzburg/is-junction and now I'm wondering, if no better solution comes up, would it be acceptable to build a solution with that?

[RyanZim]

IDK, could you just use fs.lstat or fs.stat to figure out if it's a file or directory link?

[oliversalzburg]

@RyanZim I don't see how that would be possible when it comes to detecting junctions. lstat/stat will still be necessary to distinguish the two types of symlinks, but junctions will require external help.

I have been looking for solutions the past couple of hours and nobody was able to suggest a built-in method, but I'm open for ideas :)

[RyanZim]

Sorry, I'm not very familiar with the windows filesystem, but how common are junctions?

[oliversalzburg]

That depends on the user, but, with NodeJS developers, they are more common because npm will utilize them when you install modules in certain ways (npm link or when installing a package from a local path).

Because creating junctions (or any other type of link) is not possible through the Windows GUI without third-party tools, no type of link is really common though. If they exist, they are usually created by some kind of tool.

Regardless though, creating symlinks requires elevated permissions on Windows. So in any use case where a user or tool might want to link a directory to another place, they will almost always chose a junction over a symlink.

I hope that puts it into perspective :)

[danielehrhardt]

Could this be fixed?

[RyanZim]

As per #912; fs.cp is coming to Node core, and we will be using their implementation, which is a fork of ours. If you would like this fixed, please file an issue to Node core about fs.cp.