From 0c8577f149cdc188b8a058f042ea89b8b18221ac Mon Sep 17 00:00:00 2001
From: brent saner <brent.saner@gmail.com>
Date: Thu, 3 Apr 2025 18:35:35 -0400
Subject: [PATCH] v0.1.0

ADDED:
* Explicit subnet ordering option for VLSM
---
 cmd/subnetter/args.go          |  5 +++--
 cmd/subnetter/main.go          |  1 +
 netsplit/funcs_vlsmsplitter.go | 26 ++++++++++++++------------
 netsplit/types.go              |  7 +++++++
 4 files changed, 25 insertions(+), 14 deletions(-)

diff --git a/cmd/subnetter/args.go b/cmd/subnetter/args.go
index 4fa8431..cf673e6 100644
--- a/cmd/subnetter/args.go
+++ b/cmd/subnetter/args.go
@@ -88,8 +88,9 @@ type XNetArgs struct {
 }
 
 type VLSMArgs struct {
-	Asc   bool    `short:"A" long:"ascending" description:"If specified, place smaller networks (larger prefixes) at the beginning. You almost assuredly do not want to do this."`
-	Sizes []uint8 `short:"s" long:"size" required:"true" description:"Prefix lengths. May be specified multiple times." validate:"required"`
+	Asc      bool    `short:"A" long:"ascending" description:"If specified, place smaller networks (larger prefixes) at the beginning. You almost assuredly do not want to do this."`
+	Explicit bool    `short:"O" long:"explicit-order" description:"If specified, ignore -A/--ascending and do no reordering of prefix sizes whatsoever, instead using the order given. This is EXTREMELY suboptimal and can lead to drastic addressing waste."`
+	Sizes    []uint8 `short:"s" long:"size" required:"true" description:"Prefix lengths. May be specified multiple times." validate:"required"`
 	splitArgs
 }
 
diff --git a/cmd/subnetter/main.go b/cmd/subnetter/main.go
index 646c182..085d1ad 100644
--- a/cmd/subnetter/main.go
+++ b/cmd/subnetter/main.go
@@ -172,6 +172,7 @@ func main() {
 			cmnArgs = args.VLSM.common
 			splitter = &netsplit.VLSMSplitter{
 				Ascending:     args.VLSM.Asc,
+				Explicit:      args.VLSM.Explicit,
 				PrefixLengths: args.VLSM.Sizes,
 				BaseSplitter:  new(netsplit.BaseSplitter),
 			}
diff --git a/netsplit/funcs_vlsmsplitter.go b/netsplit/funcs_vlsmsplitter.go
index 005e8a8..94704ba 100644
--- a/netsplit/funcs_vlsmsplitter.go
+++ b/netsplit/funcs_vlsmsplitter.go
@@ -2,7 +2,7 @@ package netsplit
 
 import (
 	"net/netip"
-	"sort"
+	`sort`
 
 	"go4.org/netipx"
 )
@@ -42,17 +42,19 @@ func (v *VLSMSplitter) Split() (nets []*netip.Prefix, remaining *netipx.IPSet, e
 		return
 	}
 
-	sort.SliceStable(
-		v.PrefixLengths,
-		func(i, j int) (isBefore bool) { // We use a reverse sorting by default so we get larger prefixes at the beginning.
-			if v.Ascending {
-				isBefore = v.PrefixLengths[i] > v.PrefixLengths[j]
-			} else {
-				isBefore = v.PrefixLengths[i] < v.PrefixLengths[j]
-			}
-			return
-		},
-	)
+	if !v.Explicit {
+		sort.SliceStable(
+			v.PrefixLengths,
+			func(i, j int) (isBefore bool) { // We use a reverse sorting by default so we get larger prefixes at the beginning.
+				if v.Ascending {
+					isBefore = v.PrefixLengths[i] > v.PrefixLengths[j]
+				} else {
+					isBefore = v.PrefixLengths[i] < v.PrefixLengths[j]
+				}
+				return
+			},
+		)
+	}
 
 	pfxLen, _ = v.network.Mask.Size()
 	pfxLen8 = uint8(pfxLen)
diff --git a/netsplit/types.go b/netsplit/types.go
index d21bf2c..636d9b8 100644
--- a/netsplit/types.go
+++ b/netsplit/types.go
@@ -79,6 +79,13 @@ type VLSMSplitter struct {
 		You almost assuredly do not want to do this.
 	*/
 	Ascending bool
+	/*
+		Explicit, if true, will ignore Ascending completely and split in the explicit order of PrefixLengths.
+
+		This has the potential to be *extremely* wasteful of addressing space as the resulting blocks are
+		VERY unoptimized.
+	*/
+	Explicit bool
 	// PrefixLengths contains the prefix lengths of each subnet to split out from the network.
 	PrefixLengths []uint8 `json:"prefixes" xml:"prefixes>prefix" yaml:"Prefix Lengths"`
 	*BaseSplitter `json:"net" xml:"net,omitempty" yaml:"network,omitempty"`