How to mark a file in a zip as unix executable?

I'd like to write a function like this:

func MarkFileAsExecutable(zipPath, filePath string) error

It receives a path to a zip and a file path within the zip. The goal is to use the zip package to change the ExternalAttributes of the file inside to mark it as a unix executable.

Note that marking the file as executable prior to archiving it using chmod +x isn't a solution because I need this to work on Windows. So instead I need to modify the existing zip archive accordingly.

You can use the zip package. It provides a Reader and a Writer. You open the zip archive with a reader. Then you walk the files in the archive, change your permissions as needed, and copy the files to the writer.

Here is a minimal example, without error checking:

package main
import (
	"archive/zip"
	"os"
)
func main() {
	r, _ := zip.OpenReader("example.zip")
	defer r.Close()
	f, _ := os.Create("output.zip")
	defer f.Close()
	w := zip.NewWriter(f)
	defer w.Close()
	for _, f := range r.File {
		f.SetMode(0777)
		w.Copy(f)
	}
}