You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: resolver_unix.go
    path of file: ./repos/moby/libnetwork
    
    the code of the file until where you have to start completion: //go:build !windows

package libnetwork

import (
	"fmt"
	"ne
    
func (r *Resolver) setupIPTable() error {
	if r.err != nil {
		return r.err
	}
	laddr := r.conn.LocalAddr().String()
	ltcpaddr := r.tcpListen.Addr().String()
	resolverIP, ipPort, _ := net.SplitHostPort(laddr)
	_, tcpPort, _ := net.SplitHostPort(ltcpaddr)
	rules := [][]string{
		{"-t", "nat", "-I", outputChain, "-d", resolverIP, "-p", "udp", "--dport", dnsPort, "-j", "DNAT", "--to-destination", laddr},
		{"-t", "nat", "-I", postroutingChain, "-s", resolverIP, "-p", "udp", "--sport", ipPort, "-j", "SNAT", "--to-source", ":" + dnsPort},
		{"-t", "nat", "-I", outputChain, "-d", resolverIP, "-p", "tcp", "--dport", dnsPort, "-j", "DNAT", "--to-destination", ltcpaddr},
		{"-t", "nat", "-I", postroutingChain, "-s", resolverIP, "-p", "tcp", "--sport", tcpPort, "-j", "SNAT", "--to-source", ":" + dnsPort},
	}

	var setupErr error
	err := r.backend.ExecFunc(func() {
		// TODO IPv6 support
		iptable := iptables.GetIptable(iptables.IPv4)

		// insert outputChain and postroutingchain
		if iptable.ExistsNative("nat", "OUTPUT", "-d", resolverIP, "-j", outputChain) {
			if err := iptable.RawCombinedOutputNative("-t", "nat", "-F", outputChain); err != nil {
				setupErr = err
				return
			}
		} else {
			if err := iptable.RawCombinedOutputNative("-t", "nat", "-N", outputChain); err != nil {
				setupErr = err
				return
			}
			if err := iptable.RawCombinedOutputNative("-t", "nat", "-I", "OUTPUT", "-d", resolverIP, "-j", outputChain); err != nil {
				setupErr = err
				return
			}
		}

		if iptable.ExistsNative("nat", "POSTROUTING", "-d", resolverIP, "-j", postroutingChain) {
			if err := iptable.RawCombinedOutputNative("-t", "nat", "-F", postroutingChain); err != nil {
				setupErr = err
				return
			}
		} else {
			if err := iptable.RawCombinedOutputNative("-t", "nat", "-N", postroutingChain); err != nil {
				setupErr = err
				return
			}
			if err := iptable.RawCombinedOutputNative("-t", "nat", "-I", "POSTROUTING", "-d", resolverIP, "-j", postroutingChain); err != nil {
				setupErr = err
				return
			}
		}

		for _, rule := range rules {
			if iptable.RawCombinedOutputNative(rule...) != nil {
				setupErr = fmt.Errorf("set up rule failed, %v", rule)
				return
			}
		}
	})
	if err != nil {
		return err
	}
	return setupErr
}