dnscontrol/pkg/prettyzone/sorting.go

package prettyzone

// Generate zonefiles.
// This generates a zonefile that prioritizes beauty over efficiency.

import (
	"bytes"
	"log"
	"strconv"
	"strings"

	"github.com/StackExchange/dnscontrol/v4/models"
)

// ZoneGenData is the configuration description for the zone generator.
type ZoneGenData struct {
	Origin     string
	DefaultTTL uint32
	Records    models.Records
	Comments   []string
}

func (z *ZoneGenData) Len() int      { return len(z.Records) }
func (z *ZoneGenData) Swap(i, j int) { z.Records[i], z.Records[j] = z.Records[j], z.Records[i] }
func (z *ZoneGenData) Less(i, j int) bool {
	a, b := z.Records[i], z.Records[j]

	// Sort by name.

	// If we are at the apex, use "@" in the sorting.
	compA, compB := a.NameFQDN, b.NameFQDN
	if compA != compB {
		if a.Name == "@" {
			compA = "@"
		}
		if b.Name == "@" {
			compB = "@"
		}
		return LabelLess(compA, compB)
	}

	// sub-sort by type
	if a.Type != b.Type {
		return zoneRrtypeLess(a.Type, b.Type)
	}

	// sub-sort within type:
	switch a.Type { // #rtype_variations
	case "A":
		ta2, tb2 := a.GetTargetIP(), b.GetTargetIP()
		ipa, ipb := ta2.To4(), tb2.To4()
		if ipa == nil || ipb == nil {
			log.Fatalf("should not happen: IPs are not 4 bytes: %#v %#v", ta2, tb2)
		}
		return bytes.Compare(ipa, ipb) == -1
	case "AAAA":
		ta2, tb2 := a.GetTargetIP(), b.GetTargetIP()
		ipa, ipb := ta2.To16(), tb2.To16()
		if ipa == nil || ipb == nil {
			log.Fatalf("should not happen: IPs are not 16 bytes: %#v %#v", ta2, tb2)
		}
		return bytes.Compare(ipa, ipb) == -1
	case "MX":
		// sort by priority. If they are equal, sort by Mx.
		if a.MxPreference == b.MxPreference {
			return a.GetTargetField() < b.GetTargetField()
		}
		return a.MxPreference < b.MxPreference
	case "SRV":
		//ta2, tb2 := a.(*dns.SRV), b.(*dns.SRV)
		pa, pb := a.SrvPort, b.SrvPort
		if pa != pb {
			return pa < pb
		}
		pa, pb = a.SrvPriority, b.SrvPriority
		if pa != pb {
			return pa < pb
		}
		pa, pb = a.SrvWeight, b.SrvWeight
		if pa != pb {
			return pa < pb
		}
	case "PTR":
		//ta2, tb2 := a.(*dns.PTR), b.(*dns.PTR)
		pa, pb := a.GetTargetField(), b.GetTargetField()
		if pa != pb {
			return pa < pb
		}
	case "CAA":
		//ta2, tb2 := a.(*dns.CAA), b.(*dns.CAA)
		// sort by tag
		pa, pb := a.CaaTag, b.CaaTag
		if pa != pb {
			return pa < pb
		}
		// then flag
		fa, fb := a.CaaFlag, b.CaaFlag
		if fa != fb {
			// flag set goes before ones without flag set
			return fa > fb
		}
	default:
		// pass through. String comparison is sufficient.
	}
	return a.String() < b.String()
}

// LabelLess provides a "Less" function for two labels as needed for sorting. It
// sorts labels in prefix order, to make output pretty.
func LabelLess(a, b string) bool {
	// Compare two zone labels for the purpose of sorting the RRs in a Zone.

	// If they are equal, we are done. All other code is simplified
	// because we can assume a!=b.
	if a == b {
		return false
	}

	// Sort @ at the top, then *, then everything else lexigraphically.
	// i.e. @ always is less. * is is less than everything but @.
	if a == "@" {
		return true
	}
	if b == "@" {
		return false
	}
	if a == "*" {
		return true
	}
	if b == "*" {
		return false
	}

	// Split into elements and match up last elements to first. Compare the
	// first non-equal elements.

	as := strings.Split(a, ".")
	bs := strings.Split(b, ".")
	ia := len(as) - 1
	ib := len(bs) - 1

	var min int
	if ia < ib {
		min = len(as) - 1
	} else {
		min = len(bs) - 1
	}

	// Skip the matching highest elements, then compare the next item.
	for i, j := ia, ib; min >= 0; i, j, min = i-1, j-1, min-1 {
		// Compare as[i] < bs[j]
		// Sort @ at the top, then *, then everything else.
		// i.e. @ always is less. * is is less than everything but @.
		// If both are numeric, compare as integers, otherwise as strings.

		if as[i] != bs[j] {

			// If the first element is *, it is always less.
			if i == 0 && as[i] == "*" {
				return true
			}
			if j == 0 && bs[j] == "*" {
				return false
			}

			// If the elements are both numeric, compare as integers:
			au, aerr := strconv.ParseUint(as[i], 10, 64)
			bu, berr := strconv.ParseUint(bs[j], 10, 64)
			if aerr == nil && berr == nil {
				return au < bu
			}
			// otherwise, compare as strings:
			return as[i] < bs[j]
		}
	}
	// The min top elements were equal, so the shorter name is less.
	return ia < ib
}

func zoneRrtypeLess(a, b string) bool {
	// Compare two RR types for the purpose of sorting the RRs in a Zone.

	if a == b {
		return false
	}

	// List SOAs, NSs, etc. then all others alphabetically.

	for _, t := range []string{"SOA", "NS", "CNAME",
		"A", "AAAA", "MX", "SRV", "TXT",
	} {
		if a == t {
			return true
		}
		if b == t {
			return false
		}
	}
	return a < b
}