//go:build linux

package cmd

import (
	"fmt"
	"net"

	"golang.org/x/sys/unix"
)

// peerUID returns the uid of the process on the other end of a unix socket
// connection, read from the kernel via SO_PEERCRED.
func peerUID(c net.Conn) (int, error) {
	uc, ok := c.(*net.UnixConn)
	if !ok {
		return 0, fmt.Errorf("connection is not a unix socket: %T", c)
	}
	raw, err := uc.SyscallConn()
	if err != nil {
		return 0, fmt.Errorf("raw conn: %w", err)
	}

	var cred *unix.Ucred
	var credErr error
	if err := raw.Control(func(fd uintptr) {
		cred, credErr = unix.GetsockoptUcred(int(fd), unix.SOL_SOCKET, unix.SO_PEERCRED)
	}); err != nil {
		return 0, fmt.Errorf("getsockopt control: %w", err)
	}
	if credErr != nil {
		return 0, fmt.Errorf("SO_PEERCRED: %w", credErr)
	}
	return int(cred.Uid), nil
}