v0.2.1

FIXED:
* host splitter wasn't working quite correctly; this has been fixed.

netsplit/funcs_hostsplitter.go

@@ -1,12 +1,9 @@
 package netsplit
 
 import (
-	"fmt"
 	"math/big"
-	"net"
 	"net/netip"
 
-	"github.com/projectdiscovery/mapcidr"
 	"go4.org/netipx"
 )
 
@@ -16,54 +13,84 @@ This strategy attempts to split the network into subnets of equal number of host
 
 remaining may or may not be nil depending on if the number of hosts can fit cleanly within equal network sizes on boundaries.
 
-An ErrBadNumHosts will be returned if the number of hosts does not match the *addressable* range in a prefix.
+An ErrBadNumHosts will be returned if the number of hosts does not match the *exact* number of addresses per spec in a prefix.
 */
 func (h *HostSplitter) Split() (nets []*netip.Prefix, remaining *netipx.IPSet, err error) {
 
+	var pfx netip.Prefix
 	var tgt *big.Int
+	var splitCidr int
 	var hosts *big.Int
-	var sub netip.Prefix
-	var subPtr *netip.Prefix
-	var split []*net.IPNet
-	var ipsb *netipx.IPSetBuilder = new(netipx.IPSetBuilder)
+	var found bool
+	var cs *CIDRSplitter
 
 	if h == nil || h.NumberHosts == 0 || h.BaseSplitter == nil || h.network == nil {
 		return
 	}
 
-	if split, err = mapcidr.SplitIPNetByNumber(h.network, int(h.NumberHosts)); err != nil {
+	pfx, _ = netipx.FromStdIPNet(h.network)
+	tgt = new(big.Int)
+	tgt.SetUint64(uint64(h.NumberHosts))
+
+	if NumAddrsPfx(pfx, h.InclNetAddr, h.InclBcastAddr).Cmp(tgt) < 0 {
+		// The number of hosts per-subnet exceeds the number of addresses in the specified network.
+		err = ErrNoNetSpace
+		return
+	}
+	/*
+		Iterate up through prefix lengths for the inet family's maximum length, getting larger and larger,
+		until we reach the first prefix that can contain tgt.
+		If we reach h.network.Bits(), we are forced to use that.
+		(Any case otherwise should be handled by the above checks.)
+	*/
+	for splitCidr = pfx.Addr().BitLen(); splitCidr >= pfx.Bits(); splitCidr-- {
+		if hosts, err = NumAddrsIn(uint8(splitCidr), pfx.Addr().Is6(), h.InclNetAddr, h.InclBcastAddr); err != nil {
+			return
+		}
+		if hosts.Cmp(tgt) >= 0 {
+			found = true
+			break
+		}
+	}
+	if !found {
+		// Pragmatically, we should never be able to get to this code.
+		err = ErrNoNetSpace
 		return
 	}
 
-	fmt.Println(split)
-
-	tgt = big.NewInt(0)
-	tgt.SetUint64(uint64(h.NumberHosts))
-
-	nets = make([]*netip.Prefix, len(split))
-	for idx, n := range split {
-		sub, _ = netipx.FromStdIPNet(n)
-		hosts = mapcidr.CountIPsInCIDR(false, false, n)
-		if hosts == nil || tgt.Cmp(hosts) != 0 {
-			err = &SplitErr{
-				Wrapped:            ErrBadNumHosts,
-				Nets:               nets,
-				Remaining:          remaining,
-				LastSubnet:         &sub,
-				RequestedPrefixLen: uint8(sub.Bits()),
-			}
-			ipsb.AddPrefix(sub)
-		} else {
-			subPtr = new(netip.Prefix)
-			*subPtr = sub
-			nets = append(nets, subPtr)
+	// Now that we have an appropriate prefix length for splitting, we can offload a huge portion of that to a CIDRSplitter.
+	cs = &CIDRSplitter{
+		PrefixLength: uint8(splitCidr),
+		BaseSplitter: h.BaseSplitter,
+	}
+	if nets, remaining, err = cs.Split(); err != nil {
+		return
+	}
+	// If strict mode is enabled, we then need to match the number of hosts exactly in the subnet.
+	if !h.Strict {
+		return
+	}
+	// First off, if remaining is not nil/empty, that immediately fails strict.
+	if remaining != nil && remaining.Prefixes() != nil && len(remaining.Prefixes()) != 0 {
+		err = &SplitErr{
+			Wrapped:            ErrBadNumHosts,
+			Nets:               nets,
+			Remaining:          remaining,
+			LastSubnet:         nil,
+			RequestedPrefixLen: uint8(splitCidr),
 		}
-
-		nets[idx] = new(netip.Prefix)
-		*nets[idx] = sub
+		return
 	}
 
-	if remaining, err = ipsb.IPSet(); err != nil {
+	// Then we check the cidr we split on, and check its number of hosts.
+	if hosts.Cmp(tgt) != 0 {
+		err = &SplitErr{
+			Wrapped:            ErrBadNumHosts,
+			Nets:               nets,
+			Remaining:          remaining,
+			LastSubnet:         nil,
+			RequestedPrefixLen: uint8(splitCidr),
+		}
 		return
 	}