golang nftables dump go objects

dump.go

package main

import (
	"fmt"
	"log"
	"os"

	"github.com/google/nftables"
)

func main() {
	args := os.Args[1:]
	if len(args) != 2 {
		log.Fatalf("need to specify the table and chain to list")
	}

	c, err := nftables.New()
	if err != nil {
		log.Fatalf("nftables.New() failed: %v", err)
	}

	table, err := c.ListTableOfFamily(args[0], nftables.TableFamilyINet)
	if err != nil {
		log.Fatalf("ListTableOfFamily failed: %v", err)
	}

	chain, err := c.ListChain(table, args[1])
	if err != nil {
		log.Fatalf("ListChain failed: %v", err)
	}

	rules, err := c.GetRules(table, chain)
	if err != nil {
		log.Fatalf("GetRules failed: %v", err)
	}
	for _, rule := range rules {
		log.Printf("rule position %d", rule.Position)
		for _, exp := range rule.Exprs {
			fmt.Printf("%#v\n", exp)
		}
	}
}

This makes easy to migrate from nft to google/nftables creating the rules with nft and dumping them we can obtain the necessary elements for the rules without having to parse the bytecode

                chain prerouting {
                        type nat hook prerouting priority dstnat; policy accept;
                        dnat ip to ip daddr . ip protocol . th dport map @hostport-map-v4
                        dnat ip6 to ip6 daddr . meta l4proto . th dport map @hostport-map-v6
                }

2025/01/02 12:38:08 rule position 0
&expr.Meta{Key:0xf, SourceRegister:false, Register:0x1}
&expr.Cmp{Op:0x0, Register:0x1, Data:[]uint8{0x2}}
&expr.Payload{OperationType:0x0, DestRegister:0x1, SourceRegister:0x0, Base:0x1, Offset:0x10, Len:0x4, CsumType:0x0, CsumOffset:0x0, CsumFlags:0x0}
&expr.Payload{OperationType:0x0, DestRegister:0x9, SourceRegister:0x0, Base:0x1, Offset:0x9, Len:0x1, CsumType:0x0, CsumOffset:0x0, CsumFlags:0x0}
&expr.Payload{OperationType:0x0, DestRegister:0xa, SourceRegister:0x0, Base:0x2, Offset:0x2, Len:0x2, CsumType:0x0, CsumOffset:0x0, CsumFlags:0x0}
&expr.Lookup{SourceRegister:0x1, DestRegister:0x1, IsDestRegSet:true, SetID:0x0, SetName:"hostport-map-v4", Invert:false}
&expr.NAT{Type:0x1, Family:0x2, RegAddrMin:0x1, RegAddrMax:0x1, RegProtoMin:0x9, RegProtoMax:0x9, Random:false, FullyRandom:false, Persistent:false, Prefix:false, Specified:true}
2025/01/02 12:38:08 rule position 97
&expr.Meta{Key:0xf, SourceRegister:false, Register:0x1}
&expr.Cmp{Op:0x0, Register:0x1, Data:[]uint8{0xa}}
&expr.Payload{OperationType:0x0, DestRegister:0x1, SourceRegister:0x0, Base:0x1, Offset:0x18, Len:0x10, CsumType:0x0, CsumOffset:0x0, CsumFlags:0x0}
&expr.Meta{Key:0x10, SourceRegister:false, Register:0x2}
&expr.Payload{OperationType:0x0, DestRegister:0xd, SourceRegister:0x0, Base:0x2, Offset:0x2, Len:0x2, CsumType:0x0, CsumOffset:0x0, CsumFlags:0x0}
&expr.Lookup{SourceRegister:0x1, DestRegister:0x1, IsDestRegSet:true, SetID:0x0, SetName:"hostport-map-v6", Invert:false}
&expr.NAT{Type:0x1, Family:0xa, RegAddrMin:0x1, RegAddrMax:0x1, RegProtoMin:0x2, RegProtoMax:0x2, Random:false, FullyRandom:false, Persistent:false, Prefix:false, Specified:true}