FileSystem interface: provide context, make FileInfo an interface

[fstanis]

Just a suggestion: I was looking to potentially use this project instead of golang.org/x/net/webdav and noticed the FileSystem interface is slightly different:

1. go-webdav doesn't pass a Context to its calls.
2. FileInfo is a struct and not an interface.
3. Readdir returns a []FileInfo (slice of values) but Stat returns a *FileInfo (pointer).

I was wondering if you'd consider changing this in the future? Specifically, the first two are useful for when a file system is actually remote like e.g. Dropbox or Google Drive. And using pointers in the slice is just good for consistency (and also, deep copying a slice of values has a larger overhead).

[emersion]

go-webdav doesn't pass a Context to its calls.

Yeah, context support is probably desirable.

FileInfo is a struct and not an interface.

FileInfo is just a metadata container, why would it need to be an interface?

Readdir returns a []FileInfo (slice of values) but Stat returns a *FileInfo (pointer).

Using pointers in slices is worse in this case, because each FileInfo needs to be allocated separately and the GC needs to keep track of each pointer.

[fstanis]

FileInfo is just a metadata container, why would it need to be an interface?

For example, for Google Drive it's convenient to keep additional information, such as an ID. Using an interface means I can reuse the same internal structure, as opposed to making a copy to be compatible with go-webdav. An interface also gives a guarantee that go-webdav doesn't mutate the structs.

I agree on the GC overhead for a slice of points, but this may be premature optimization. Specifically, I'm worried that many file system implementations would keep a cache of FileInfo objects somewhere in a different structure (e.g. a tree) and would then need to construct a slice when Readdir is called, effectively copying a lot of data. With pointers, there would only be slice construction overhead, the underlying data wouldn't be copied.

[emersion]

See also: https://go.googlesource.com/proposal/+/master/design/draft-iofs.md

[emersion]

The io/fs package has been merged: https://tip.golang.org/pkg/io/fs/

[emersion]

context has been plumbed through now.

For example, for Google Drive it's convenient to keep additional information, such as an ID. Using an interface means I can reuse the same internal structure, as opposed to making a copy to be compatible with go-webdav. An interface also gives a guarantee that go-webdav doesn't mutate the structs.

This doesn't really help, a slice of []*customFileInfo can't be cast directly to a []webdav.FileInfo when webdav.FileInfo is an interface. Some amount of copying is required either way, and I don't think filling the webdav struct is that much work.