//go:build linux

package main

import (
	"fmt"
	"net"
	"os"
	"strconv"
	"strings"
	"syscall"
)

// peerCred returns the uid and pid of the process on the other end of a unix socket (kernel-verified).
func peerCred(c net.Conn) (uid, pid int, err error) {
	uc, ok := c.(*net.UnixConn)
	if !ok {
		return -1, 0, fmt.Errorf("not a unix connection")
	}
	raw, err := uc.SyscallConn()
	if err != nil {
		return -1, 0, err
	}
	uid = -1
	var gerr error
	raw.Control(func(fd uintptr) {
		cred, err := syscall.GetsockoptUcred(int(fd), syscall.SOL_SOCKET, syscall.SO_PEERCRED)
		if err != nil {
			gerr = err
			return
		}
		uid, pid = int(cred.Uid), int(cred.Pid)
	})
	return uid, pid, gerr
}

// peerExe is the program the process runs (a replaced program shows as "... (deleted)": the name is what matters).
func peerExe(pid int) (string, error) {
	p, err := os.Readlink("/proc/" + strconv.Itoa(pid) + "/exe")
	return strings.TrimSuffix(p, " (deleted)"), err
}