//go:build linux

package instancectl

import (
	"fmt"
	"net"
	"os"

	"github.com/carlosframework/platform/internal/safefile"
	"golang.org/x/sys/unix"
)

func claimListenExecSocket(source string) (*net.UnixListener, error) {
	dir, err := safefile.OpenDir(source)
	if err != nil {
		return nil, err
	}
	defer dir.Close()
	var parent unix.Stat_t
	if err := unix.Fstat(int(dir.Fd()), &parent); err != nil {
		return nil, err
	}
	if parent.Uid != uint32(os.Geteuid()) || parent.Mode&0022 != 0 {
		return nil, ErrClaimUnit
	}
	path := fmt.Sprintf("/proc/self/fd/%d/exec.sock", dir.Fd())
	ln, err := net.ListenUnix("unix", &net.UnixAddr{Name: path, Net: "unix"})
	if err != nil {
		return nil, err
	}
	ln.SetUnlinkOnClose(false)
	fail := func(err error) (*net.UnixListener, error) { ln.Close(); return nil, err }
	fd, err := unix.Openat(int(dir.Fd()), "exec.sock", unix.O_PATH|unix.O_NOFOLLOW|unix.O_CLOEXEC, 0)
	if err != nil {
		return fail(err)
	}
	defer unix.Close(fd)
	var st unix.Stat_t
	if err := unix.Fstat(fd, &st); err != nil {
		return fail(err)
	}
	if st.Mode&unix.S_IFMT != unix.S_IFSOCK || st.Uid != uint32(os.Geteuid()) {
		return fail(ErrClaimUnit)
	}
	if err := unix.Fchmodat(fd, "", 0666, unix.AT_EMPTY_PATH); err != nil {
		return fail(err)
	}
	return ln, nil
}