archive/tar: decide before go1.22 whether the FileInfoNames interface is Unix-only use

[qiulaidongfeng]

Update : #65245 (comment) And #65245 (comment)

#50102 add FileInfoNames interface to archive/tar
I in August 2023 by https://go-review.googlesource.com/c/go/+/514235 wrote an implementation for the proposal

(My CL only has a complete implementation for changing FileInfoHeader behavior on unix.)

See https://pkg.go.dev/os/user#User , seems that there is no guarantee that uid and gid for non Unix systems are of type int.

This need to be resolved before go1.22 is released, in case it cannot be resolved in a backward compatible way in the future.

Possible solutions:

1. Modify https://github.com/golang/go/blob/master/src/archive/tar/common.go#L645C1-L647C45 and https://github.com/golang/go/blob/master/src/archive/tar/common.go#L742C1-L743C34, said change FileInfoHeader behaviors on Unix only. This is the easiest.
2. Delete the existing FileInfoNames interface in go1.22 .

[gopherbot]

Change https://go.dev/cl/556399 mentions this issue: doc/go1.22: make the description of FileInfoNames conform to the implementation

[qiulaidongfeng]

cc @dsnet because https://dev.golang.org/owners

[qiulaidongfeng]

More information:
The FileInfoNames interface added to #50102 is proposed here : #50102 (comment)

The reason this interface only changed FileInfoHeader behavior on unix was that we didn't know how non-Unix systems like windows could get uid and gid from fs.FileInfo.

I just reviewed #50102, and it seems that this interface is designed to avoid any id ->name lookups.
The behavior of any id ->name lookups only exists in Unix systems.

Looks like that's what we're going to do here:

Modify https://github.com/golang/go/blob/master/src/archive/tar/common.go#L645C1-L647C45 and https://github.com/golang/go/blob/master/src/archive/tar/common.go#L742C1-L743C34, said change FileInfoHeader behaviors on Unix only. This is the easiest.

I'll send a CL later to do that.

My understanding of the non Unix uid and gid only from https://pkg.go.dev/os/user#User.
From what I can tell, this interface is unlikely to change the behavior of FileInfoHeader on non-Unix systems.
If you disagree, please comment as soon as possible.
This is because once go1.22 is released there will be no way to modify the FileInfoNames interface in a backward-compatible way.

[gopherbot]

Change https://go.dev/cl/558135 mentions this issue: archive/tar: make it clear FileInfoNames change FileInfoHeader behavior only in unix

[qiulaidongfeng]

Sorry, my description of the implementation wasn't quite right.
I now realize that because loadUidAndGid is only implemented on unix systems, FileInfoNames would provide the wrong semantics for non-Unix systems. Unless fs.FileInfo.Sys() provides tar.Header, FileInfoNames.Uname and FileInfoNames.Gname simply receive uid and gid of 0.

[qiulaidongfeng]

I suggest FileInfoNames changing FileInfoHeader behavior on unix only at go1.22 .
Because it seems that this interface is designed to avoid any id ->name lookups.
The behavior of any id ->name lookups only exists in Unix systems.

[bcmills]

The os/user.User struct uses string values for the Uid and Gid fields to allow it to be implemented portably. It seems like we should probably do the same for the FileInfoNames interface.

Since this is a new feature in Go 1.22 and we're very deep into the release cycle at this point, we should probably roll back the API addition and send it back through proposal review to revise the interface.

[gopherbot]

Change https://go.dev/cl/558295 mentions this issue: Revert "archive/tar: add FileInfoNames interface"