archive/zip: FileInfoHeader does not handle directories

[dsnet]

Consider the following:

fi, _ := os.Stat("/home/")
h, _ := zip.FileInfoHeader(fi)
fmt.Println(h.Name)

This currently prints:

home

However, ZIP treats directories as files with a trailing "/" in the name, which FileInfoHeader should automatically append if os.FileInfo.IsDir reports true.

This difference is minor since users are usually expected to replace the FileHeader.Name shortly afterwards anyways.

[ianlancetaylor]

@dsnet Please update milestone. Thanks.

[gopherbot]

Change https://golang.org/cl/124155 mentions this issue: archive/zip: fix regression when writing directories

[dsnet]

We should fix this. I found several cases where users are explicitly doing something like this:

fh, err := zip.FileInfoHeader(fi)
if err != nil {
    return err
}
if fi.IsDir() {
    fh.Name += "/"
}

Also, per CL/124155, the function should avoid setting the size for directories.

EDIT: Will have to think about what happens with existing code, since this will result in "/" appended twice.

[ianlancetaylor]

@dsnet Is anything going to happen here for 1.12?

[dsnet]

This change has a risk of breaking people. Too late for 1.12. We'll submit early 1.13.