feature: add divide subcommand

README.md

@@ -93,9 +93,53 @@ This also works with IPv6 CIDR ranges, for example:
 
 ```
 $ cidr overlaps 2001:db8:1111:2222:1::/80 2001:db8:1111:2222:1:1::/96
-true
+
 ```
 
+### CIDR division
+
+To divide a CIDR range into N distinct networks:
+## IPV4
+```
+$ cidr divide 10.0.0.0/16 9
+  [Networks]
+10.0.0.0/20
+10.0.16.0/20
+10.0.32.0/20
+10.0.48.0/20
+10.0.64.0/20
+10.0.80.0/20
+10.0.96.0/20
+10.0.112.0/20
+10.0.128.0/20
+```
+
+## IPV6
+```
+$ cidr divide 2001:db8:1111:2222:1::/80 9
+  [Networks]
+2001:db8:1111:2222:1::/84
+2001:db8:1111:2222:1:1000::/84
+2001:db8:1111:2222:1:2000::/84
+2001:db8:1111:2222:1:3000::/84
+2001:db8:1111:2222:1:4000::/84
+2001:db8:1111:2222:1:5000::/84
+2001:db8:1111:2222:1:6000::/84
+2001:db8:1111:2222:1:7000::/84
+2001:db8:1111:2222:1:8000::/84
+
+```
+
+You can also use the `-u` flag to divide the network based on the number of desired host addresses. This calculation includes a broadcast and gateway address, so you only need to consider the host addresses.
+The command below shows how to divide a CIDR range to accommodate a minimum of 32 hosts, 30 hosts, and 12 hosts. It also provides the total possible hosts available for a subnet.
+```
+$ cidr d 192.168.0.0/24 -u 32,30,12
+  [Networks]            [Used]  [Total]
+192.168.0.0/26            32      62
+192.168.0.64/27           30      30
+192.168.0.96/28           12      14
+
+```
 ## Contributing
 
 Contributions are highly appreciated and always welcome.

cmd/cmd_tests/count_test.go

@@ -0,0 +1,43 @@
+// Copyright (c) Bruno Schaatsbergen
+// SPDX-License-Identifier: MIT
+
+package cmd_test
+
+import (
+	"math/big"
+	"net"
+	"testing"
+
+	"github.com/bschaatsbergen/cidr/pkg/core"
+)
+
+func TestGetAddressCount(t *testing.T) {
+	testCases := []struct {
+		cidr     string
+		expected *big.Int
+	}{
+		// Common IPv4 cases
+		{"10.0.0.0/24", big.NewInt(256)},
+		{"192.168.1.0/28", big.NewInt(16)},
+		{"172.16.0.0/12", big.NewInt(1048576)},
+		// IPv4 edge cases
+		{"192.168.0.0/31", big.NewInt(2)},
+		{"10.10.10.10/32", big.NewInt(1)},
+		// IPv6 cases
+		{"2001:db8::/32", big.NewInt(0).Lsh(big.NewInt(1), 96)}, // [128 - 32 -> 2^96 ]
+		{"fe80::/64", big.NewInt(0).Lsh(big.NewInt(1), 64)},     // [128 - 64 -> 2^64 ]
+		{"::1/128", big.NewInt(1)},
+	}
+
+	for _, tc := range testCases {
+		_, ipNet, err := net.ParseCIDR(tc.cidr)
+		if err != nil {
+			t.Fatalf("Failed to parse CIDR %s: %v", tc.cidr, err)
+		}
+
+		actual := core.GetAddressCount(ipNet)
+		if actual.Cmp(tc.expected) != 0 {
+			t.Errorf("For CIDR %s, expected address count %d, but got %d", tc.cidr, tc.expected, actual)
+		}
+	}
+}

cmd/cmd_tests/divide_test.go

@@ -0,0 +1,126 @@
+// Copyright (c) Bruno Schaatsbergen
+// SPDX-License-Identifier: MIT
+
+package cmd_test
+
+import (
+	"fmt"
+	"net"
+	"testing"
+	"github.com/bschaatsbergen/cidr/pkg/core"
+)
+
+func TestDivideCidr(t *testing.T) {
+	testCases := []struct {
+		cidr      string
+		divisor   int64
+		expected  []string // Expected CIDRs in string format
+		shouldErr bool
+	}{
+		{"10.0.0.0/16", 2, []string{"10.0.0.0/17", "10.0.128.0/17"}, false},
+		{"192.168.0.0/24", 4, []string{"192.168.0.0/26", "192.168.0.64/26", "192.168.0.128/26", "192.168.0.192/26"}, false},
+		{"2001:db8::/32", 3, []string{"2001:db8::/34", "2001:db8:4000::/34", "2001:db8:8000::/34"}, false},
+		// Error cases
+		{"10.0.0.0/16", 0, nil, true},    // Divisor is zero
+		{"2001:db8::/128", 3, nil, true}, // Cannot divide /128
+	}
+
+	for _, tc := range testCases {
+		_, ipNet, err := net.ParseCIDR(tc.cidr)
+		if err != nil && !tc.shouldErr {
+			t.Errorf("Unexpected error parsing CIDR: %s", err)
+			continue
+		}
+
+		subnets, err := core.DivideCidr(ipNet, tc.divisor)
+
+		if tc.shouldErr {
+			if err == nil {
+				t.Errorf("Expected error for CIDR %s, divisor %d, but got none", tc.cidr, tc.divisor)
+			}
+			continue
+		}
+
+		if err != nil {
+			t.Errorf("Unexpected error for CIDR %s, divisor %d: %s", tc.cidr, tc.divisor, err)
+			continue
+		}
+
+		if len(subnets) != len(tc.expected) {
+			t.Errorf("Incorrect number of subnets for CIDR %s, divisor %d: expected %d, got %d", tc.cidr, tc.divisor, len(tc.expected), len(subnets))
+			continue
+		}
+
+		for i, expectedCIDR := range tc.expected {
+			if subnets[i].String() != expectedCIDR {
+				t.Errorf("Incorrect subnet %d for CIDR %s, divisor %d: expected %s, got %s", i, tc.cidr, tc.divisor, expectedCIDR, subnets[i].String())
+			}
+		}
+	}
+}
+
+func TestDivideCidrHosts(t *testing.T) {
+	testCases := []struct {
+		inputCIDR    string
+		desiredUsers []int64
+		expectedNets []string
+		expectedErr  error
+	}{
+		{"192.168.0.0/24", []int64{20, 10, 30}, []string{"192.168.0.0/27", "192.168.0.32/28", "192.168.0.48/27"}, nil},
+		{"10.0.0.0/16", []int64{1000, 500}, []string{"10.0.0.0/22", "10.0.4.0/23"}, nil},
+		{"2001:db8::/32", []int64{50000}, []string{"2001:db8::/112"}, nil},
+		{"192.168.0.0/24", []int64{}, []string{}, nil},                                                                              // Edge case: empty desiredUsers
+		{"192.168.0.0/24", []int64{257}, nil, fmt.Errorf("Total address space is: 256 but desired Hosts requires 512 addresses\n")}, // Edge case: not enough addresses
+	}
+
+	for _, tc := range testCases {
+		_, ipNet, err := net.ParseCIDR(tc.inputCIDR)
+		if err != nil && tc.expectedErr == nil {
+			t.Fatalf("Failed to parse CIDR: %v", err)
+		}
+
+		validatedHosts, err := core.ValidateHostSpace(ipNet, tc.desiredUsers)
+		if tc.expectedErr != nil {
+			if err == nil || err.Error() != tc.expectedErr.Error() {
+				t.Errorf("A: For %s, users %v: Expected error '%v', got '%v'", tc.inputCIDR, tc.desiredUsers, tc.expectedErr, err)
+			}
+			continue
+		}
+
+		networks, err := core.DivideCidrHosts(ipNet, validatedHosts)
+
+		if tc.expectedErr != nil {
+			if err == nil || err.Error() != tc.expectedErr.Error() {
+				t.Errorf("A: For %s, users %v: Expected error '%v', got '%v'", tc.inputCIDR, tc.desiredUsers, tc.expectedErr, err)
+			}
+			continue
+		}
+
+		if err != nil {
+			t.Errorf("B: For %s, users %v: Unexpected error '%v'", tc.inputCIDR, tc.desiredUsers, err)
+			continue
+		}
+
+		netStrings := make([]string, len(networks))
+		for i, n := range networks {
+			netStrings[i] = n.String()
+		}
+
+		if !equalStringSlices(netStrings, tc.expectedNets) {
+			fmt.Println(networks)
+			t.Errorf("C: For %s, users %v: Expected subnets '%v', got '%v'", tc.inputCIDR, tc.desiredUsers, tc.expectedNets, netStrings)
+		}
+	}
+}
+
+func equalStringSlices(a, b []string) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i, v := range a {
+		if v != b[i] {
+			return false
+		}
+	}
+	return true
+}

cmd/count.go

@@ -5,6 +5,7 @@ package cmd
 
 import (
 	"fmt"
+	"math/big"
 	"net"
 	"os"
 
@@ -48,7 +49,7 @@ func init() {
 	rootCmd.AddCommand(countCmd)
 }
 
-func count(network *net.IPNet) uint64 {
+func count(network *net.IPNet) *big.Int {
 	count := core.GetAddressCount(network)
 	return count
 }