conntrack.go

package main

import (
	"fmt"
	"errors"
	"encoding/binary"
	"syscall"
)

func main() {
	dump1 := []byte{52, 0, 1, 128, 20, 0, 1, 128, 8, 0, 1, 0, 172, 17, 0, 2, 8, 0, 2, 0, 192, 168, 65, 1, 28, 0, 2, 128, 5, 0, 1, 0, 17, 0, 0, 0, 6, 0, 2, 0, 215, 32, 0, 0, 6, 0, 3, 0, 0, 53, 0, 0, 52, 0, 2, 128, 20, 0, 1, 128, 8, 0, 1, 0, 192, 168, 65, 1, 8, 0, 2, 0, 172, 17, 0, 2, 28, 0, 2, 128, 5, 0, 1, 0, 17, 0, 0, 0, 6, 0, 2, 0, 0, 53, 0, 0, 6, 0, 3, 0, 215, 32, 0, 0, 8, 0, 12, 0, 239, 175, 148, 0, 8, 0, 3, 0, 0, 0, 0, 8, 8, 0, 7, 0, 0, 0, 0, 30}
	dump2 := []byte{52, 0, 1, 128, 20, 0, 1, 128, 8, 0, 1, 0, 172, 17, 0, 2, 8, 0, 2, 0, 192, 168, 65, 1, 28, 0, 2, 128, 5, 0, 1, 0, 17, 0, 0, 0, 6, 0, 2, 0, 183, 16, 0, 0, 6, 0, 3, 0, 0, 53, 0, 0, 52, 0, 2, 128, 20, 0, 1, 128, 8, 0, 1, 0, 192, 168, 65, 1, 8, 0, 2, 0, 172, 17, 0, 2, 28, 0, 2, 128, 5, 0, 1, 0, 17, 0, 0, 0, 6, 0, 2, 0, 0, 53, 0, 0, 6, 0, 3, 0, 183, 16, 0, 0, 8, 0, 12, 0, 239, 177, 130, 0, 8, 0, 3, 0, 0, 0, 0, 10, 8, 0, 7, 0, 0, 0, 0, 30}
	dump3 := []byte{60, 0, 1, 128, 20, 0, 1, 128, 8, 0, 1, 0, 172, 17, 0, 2, 8, 0, 2, 0, 172, 217, 0, 14, 36, 0, 2, 128, 5, 0, 1, 0, 1, 0, 0, 0, 6, 0, 4, 0, 12, 155, 0, 0, 5, 0, 5, 0, 8, 0, 0, 0, 5, 0, 6, 0, 0, 0, 0, 0, 60, 0, 2, 128, 20, 0, 1, 128, 8, 0, 1, 0, 172, 217, 0, 14, 8, 0, 2, 0, 172, 17, 0, 2, 36, 0, 2, 128, 5, 0, 1, 0, 1, 0, 0, 0, 6, 0, 4, 0, 12, 155, 0, 0, 5, 0, 5, 0, 0, 0, 0, 0, 5, 0, 6, 0, 0, 0, 0, 0, 8, 0, 12, 0, 239, 177, 139, 0, 8, 0, 3, 0, 0, 0, 0, 8, 8, 0, 7, 0, 0, 0, 0, 30}
	dump4 := []byte{60, 0, 1, 128, 20, 0, 1, 128, 8, 0, 1, 0, 172, 17, 0, 2, 8, 0, 2, 0, 172, 217, 0, 14, 36, 0, 2, 128, 5, 0, 1, 0, 1, 0, 0, 0, 6, 0, 4, 0, 12, 155, 0, 0, 5, 0, 5, 0, 8, 0, 0, 0, 5, 0, 6, 0, 0, 0, 0, 0, 60, 0, 2, 128, 20, 0, 1, 128, 8, 0, 1, 0, 172, 217, 0, 14, 8, 0, 2, 0, 172, 17, 0, 2, 36, 0, 2, 128, 5, 0, 1, 0, 1, 0, 0, 0, 6, 0, 4, 0, 12, 155, 0, 0, 5, 0, 5, 0, 0, 0, 0, 0, 5, 0, 6, 0, 0, 0, 0, 0, 8, 0, 12, 0, 239, 177, 139, 0, 8, 0, 3, 0, 0, 0, 0, 10, 8, 0, 7, 0, 0, 0, 0, 30}
	dump5 := []byte{60, 0, 1, 128, 20, 0, 1, 128, 8, 0, 1, 0, 172, 17, 0, 2, 8, 0, 2, 0, 172, 217, 0, 14, 36, 0, 2, 128, 5, 0, 1, 0, 1, 0, 0, 0, 6, 0, 4, 0, 12, 155, 0, 0, 5, 0, 5, 0, 8, 0, 0, 0, 5, 0, 6, 0, 0, 0, 0, 0, 60, 0, 2, 128, 20, 0, 1, 128, 8, 0, 1, 0, 172, 217, 0, 14, 8, 0, 2, 0, 172, 17, 0, 2, 36, 0, 2, 128, 5, 0, 1, 0, 1, 0, 0, 0, 6, 0, 4, 0, 12, 155, 0, 0, 5, 0, 5, 0, 0, 0, 0, 0, 5, 0, 6, 0, 0, 0, 0, 0, 8, 0, 12, 0, 239, 177, 139, 0, 8, 0, 3, 0, 0, 0, 2, 10}
	dump6 := []byte{52, 0, 1, 128, 20, 0, 1, 128, 8, 0, 1, 0, 172, 17, 0, 2, 8, 0, 2, 0, 192, 168, 65, 1, 28, 0, 2, 128, 5, 0, 1, 0, 17, 0, 0, 0, 6, 0, 2, 0, 183, 16, 0, 0, 6, 0, 3, 0, 0, 53, 0, 0, 52, 0, 2, 128, 20, 0, 1, 128, 8, 0, 1, 0, 192, 168, 65, 1, 8, 0, 2, 0, 172, 17, 0, 2, 28, 0, 2, 128, 5, 0, 1, 0, 17, 0, 0, 0, 6, 0, 2, 0, 0, 53, 0, 0, 6, 0, 3, 0, 183, 16, 0, 0, 8, 0, 12, 0, 239, 177, 130, 0, 8, 0, 3, 0, 0, 0, 2, 10}
	
	parse1, _ := parseAttrs(dump1)
	fmt.Printf("%v\n", parse1)
	parse2, _ := parseAttrs(dump2)
	fmt.Printf("%v\n", parse2)
	parse3, _ := parseAttrs(dump3)
	fmt.Printf("%v\n", parse3)
	parse4, _ := parseAttrs(dump4)
	fmt.Printf("%v\n", parse4)
	parse5, _ := parseAttrs(dump5)
	fmt.Printf("%v\n", parse5)
	parse6, _ := parseAttrs(dump6)
	fmt.Printf("%v\n", parse6)
}

const (
	// #defined in libnfnetlink/include/libnfnetlink/libnfnetlink.h
	NLA_F_NESTED        = uint16(1 << 15)
	NLA_F_NET_BYTEORDER = uint16(1 << 14)
	NLA_TYPE_MASK       = ^(NLA_F_NESTED | NLA_F_NET_BYTEORDER)

	NLM_F_EXCL   = 0x200
	NLM_F_CREATE = 0x400
)

const attrHdrLength = 4

type Attr struct {
	Msg            []byte
	Typ            int
	IsNested       bool
	IsNetByteorder bool
	Attrs          []Attr
}

func parseAttrs(b []byte) ([]Attr, error) {
	var attrs []Attr
	for len(b) >= attrHdrLength {
		var attr Attr
		attr, b = parseAttr(b)
		attrs = append(attrs, attr)
	}

	if len(b) != 0 {
		return nil, errors.New("leftover attr bytes")
	}
	return attrs, nil
}

func parseAttr(b []byte) (Attr, []byte) {
	attrLen := binary.LittleEndian.Uint16(b[0:2])
	// length is header + payload
	attrLen -= uint16(attrHdrLength)

	typ := binary.LittleEndian.Uint16(b[2:4])
	attr := Attr{
		Msg:            b[attrHdrLength : attrHdrLength+int(attrLen)],
		Typ:            int(typ & NLA_TYPE_MASK),
		IsNested:       typ&NLA_F_NESTED > 0,
		IsNetByteorder: typ&NLA_F_NET_BYTEORDER > 0,
	}

	if attr.IsNested {
		attr.Attrs, _ = parseAttrs(attr.Msg)
	}

	return attr, b[rtaAlignOf(attrHdrLength+int(attrLen)):]
}

// Round the length of a netlink route attribute up to align it
// properly.
func rtaAlignOf(attrlen int) int {
	return (attrlen + syscall.RTA_ALIGNTO - 1) & ^(syscall.RTA_ALIGNTO - 1)
}