Canonicalize CIDR
You are encouraged to solve this task according to the task description, using any language you may know.
- Task
Implement a function or program that, given a range of IPv4 addresses in CIDR notation (dotted-decimal/network-bits), will return/output the same range in canonical form.
That is, the IP address portion of the output CIDR block must not contain any set (1) bits in the host part of the address.
- Example
Given 87.70.141.1/22, your code should output 87.70.140.0/22
- Explanation
An Internet Protocol version 4 address is a 32-bit value, conventionally represented as a number in base 256 using dotted-decimal notation, where each base-256 "digit" is represented by the digit value in decimal and the digits are separated by periods. Logically, this 32-bit value represents two components: the leftmost (most-significant) bits determine the "network" portion of the address, while the rightmost (least-significant) bits determine the "host" portion. Classless Internet Domain Routing block notation indicates where the boundary between these two components is for a given address by adding a slash followed by the number of bits in the network portion.
In general, CIDR blocks stand in for the entire set of IP addresses sharing the same "network" component; it's common to see access control lists specify a single IP address using CIDR with /32 to indicate that only the one address is included. Often, the tools using this notation expect the address to be entered in canonical form, in which the "host" bits are all zeroes in the binary representation. But careless network admins may provide CIDR blocks without canonicalizing them first. This task handles the canonicalization.
The example address, 87.70.141.1, translates into 01010111010001101000110100000001 in binary notation zero-padded to 32 bits. The /22 means that the first 22 of those bits determine the match; the final 10 bits should be 0. But they instead include two 1 bits: 0100000001. So to canonicalize the address, change those 1's to 0's to yield 01010111010001101000110000000000, which in dotted-decimal is 87.70.140.0.
C
This solution uses only the standard library. On POSIX platforms one can use the functions inet_pton/inet_ntop to parse/format IPv4 addresses. <lang c>#include <stdbool.h>
- include <stdio.h>
- include <stdint.h>
typedef struct cidr_tag {
uint32_t address; uint32_t mask;
} cidr_t;
// Convert a string in CIDR format to an IPv4 address and netmask, // if possible. Also performs CIDR canonicalization. bool cidr_parse(const char* str, cidr_t* cidr) {
int a, b, c, d, m;
if (sscanf(str, "%d.%d.%d.%d/%d", &a, &b, &c, &d, &m) != 5)
return false;
if (m < 1 || m > 32)
return false;
if (a < 0 || a > UINT8_MAX)
return false;
if (b < 0 || b > UINT8_MAX)
return false;
if (c < 0 || c > UINT8_MAX)
return false;
if (d < 0 || d > UINT8_MAX)
return false;
uint32_t mask = ~((1 << (32 - m)) - 1);
uint32_t address = (a << 24) + (b << 16) + (c << 8) + d;
address &= mask;
cidr->address = address;
cidr->mask = mask;
return true;
}
uint8_t mask_length(uint32_t mask) {
uint8_t length = 32;
for (; (mask & 1) == 0 && length > 0; mask >>= 1, --length) {}
return length;
}
// Write a string in CIDR notation into the supplied buffer. void cidr_format(const cidr_t* cidr, char* str, size_t size) {
uint8_t m = mask_length(cidr->mask); uint32_t address = cidr->address; uint8_t d = address & UINT8_MAX; address >>= 8; uint8_t c = address & UINT8_MAX; address >>= 8; uint8_t b = address & UINT8_MAX; address >>= 8; uint8_t a = address & UINT8_MAX; snprintf(str, size, "%hhu.%hhu.%hhu.%hhu/%hhu", a, b, c, d, m);
}
int main(int argc, char** argv) {
for (int i = 1; i < argc; ++i) {
cidr_t cidr;
if (cidr_parse(argv[i], &cidr)) {
char out[32];
cidr_format(&cidr, out, sizeof(out));
puts(out);
} else {
fprintf(stderr, "%s: invalid CIDR\n", argv[i]);
}
}
return 0;
}</lang>
- Output:
$ ./canonicalize_cidr 87.70.141.1/22 87.70.140.0/22
Factor
<lang factor>USING: command-line formatting grouping io kernel math.parser namespaces prettyprint sequences splitting ; IN: rosetta-code.canonicalize-cidr
! canonicalize a CIDR block: make sure none of the host bits are set command-line get [ lines ] when-empty [
! ( CIDR-IP -- bits-in-network-part dotted-decimal ) "/" split first2 string>number swap
! get IP as binary string "." split [ string>number "%08b" sprintf ] map "" join
! replace the host part with all zeros over cut length [ CHAR: 0 ] "" replicate-as append
! convert back to dotted-decimal 8 group [ bin> number>string ] map "." join swap
! and output "%s/%d\n" printf
] each</lang>
- Output:
$ canonicalize-cidr.factor 87.70.141.1/22 87.70.140.0/22
Go
<lang go>package main
import (
"fmt" "log" "os" "strconv" "strings"
)
func check(err error) {
if err != nil {
log.Fatal(err)
}
}
func main() {
// canonicalize a CIDR block: make sure none of the host bits are set
var cidr string
if len(os.Args) > 1 {
cidr = os.Args[1]
} else {
log.Fatal("Please pass the CIDR to be canonicalized.")
}
// dotted-decimal / bits in network part split := strings.Split(cidr, "/") dotted := split[0] size, err := strconv.Atoi(split[1]) check(err)
// get IP as binary string
var bin []string
for _, n := range strings.Split(dotted, ".") {
i, err := strconv.Atoi(n)
check(err)
bin = append(bin, fmt.Sprintf("%08b", i))
}
binary := strings.Join(bin, "")
// replace the host part with all zeros
binary = binary[0:size] + strings.Repeat("0", 32-size)
// convert back to dotted-decimal
var canon []string
for i := 0; i < len(binary); i += 8 {
num, err := strconv.ParseInt(binary[i:i+8], 2, 64)
check(err)
canon = append(canon, fmt.Sprintf("%d", num))
}
// and output
fmt.Printf("%s/%s\n", strings.Join(canon, "."), split[1])
}</lang>
- Output:
$ go run canonicalize_cidr.go 87.70.141.1/22 87.70.140.0/22
Julia
Julia has a Sockets library as a builtin, which has the types IPv4 and IPv6 for single IP addresses. <lang julia>using Sockets
function canonCIDR(cidr::String)
cidr = replace(cidr, r"\.(\.|\/)" => s".0\1") # handle .. cidr = replace(cidr, r"\.(\.|\/)" => s".0\1") # handle ... ip = split(cidr, "/") dig = length(ip) > 1 ? 2^(32 - parse(UInt8, ip[2])) : 1 ip4 = IPv4(UInt64(IPv4(ip[1])) & (0xffffffff - dig + 1)) return length(ip) == 1 ? "$ip4" : "$ip4/$(ip[2])"
end
println(canonCIDR("87.70.141.1/22")) println(canonCIDR("100.68.0.18/18")) println(canonCIDR("10.4.30.77/30")) println(canonCIDR("110.200.21/4")) println(canonCIDR("10..55/8")) println(canonCIDR("10.../8"))
</lang>
- Output:
87.70.140.0/22 100.68.0.0/18 10.4.30.76/30 96.0.0.0/4 10.0.0.0/8 10.0.0.0/8
Perl
<lang perl>#!/usr/bin/env perl use v5.16; use Socket qw(inet_aton inet_ntoa);
- canonicalize a CIDR block: make sure none of the host bits are set
if (!@ARGV) {
chomp(@ARGV = <>);
}
for (@ARGV) {
# dotted-decimal / bits in network part my ($dotted, $size) = split m#/#;
# get IP as binary string
my $binary = sprintf "%032b", unpack('N', inet_aton $dotted);
# Replace the host part with all zeroes substr($binary, $size) = 0 x (32 - $size);
# Convert back to dotted-decimal $dotted = inet_ntoa(pack 'B32', $binary);
# And output say "$dotted/$size";
}</lang>
- Output:
$ canonicalize_cidr.pl 87.70.141.1/22 87.70.140.0/22
Python
<lang python>#!/usr/bin/env python
- canonicalize a CIDR block specification:
- make sure none of the host bits are set
import sys from socket import inet_aton, inet_ntoa from struct import pack, unpack
args = sys.argv[1:] if len(args) == 0:
args = sys.stdin.readlines()
for cidr in args:
# IP in dotted-decimal / bits in network part
dotted, size_str = cidr.split('/')
size = int(size_str)
numeric = unpack('!I', inet_aton(dotted))[0] # IP as an integer
binary = f'{numeric:#034b}' # then as a padded binary string
prefix = binary[:size + 2] # just the network part
# (34 and +2 are to account
# for leading '0b')
canon_binary = prefix + '0' * (32 - size) # replace host part with all zeroes
canon_numeric = int(canon_binary, 2) # convert back to integer
canon_dotted = inet_ntoa(pack('!I',
(canon_numeric))) # and then to dotted-decimal
print(f'{canon_dotted}/{size}') # output result</lang>
- Output:
$ canonicalize_cidr.py 87.70.141.1/22 87.70.140.0/22
Raku
<lang perl6>#!/usr/bin/env raku
- canonicalize a CIDR block: make sure none of the host bits are set
if (!@*ARGS) {
@*ARGS = $*IN.lines;
}
for @*ARGS -> $cidr {
# dotted-decimal / bits in network part
my ($dotted, $size) = $cidr.split('/');
# get IP as binary string
my $binary = $dotted.split('.').map({ .fmt("%08b") }).join;
# Replace the host part with all zeroes $binary.substr-rw($size) = 0 x (32 - $size);
# Convert back to dotted-decimal
my $canon = $binary.comb.batch(8).map({ .join.parse-base(2) }).join('.');
# And output say "$canon/$size";
}</lang>
- Output:
$ canonicalize_cidr.raku 87.70.141.1/22 87.70.140.0/22
REXX
<lang rexx>/*REXX pgm canonicalizes IPv4 addresses that are in CIDR notation (dotted─dec/network).*/ parse arg z . /*obtain optional argument from the CL.*/ if z== | z=="," then z= '87.70.141.1/22' /*Not specified? Then use the default.*/ parse var z # '/' -0 mask /*get the address nodes & netaddr mask.*/ size= d2b( word( substr(mask, 2) 1, 1 ) ) /*size of binary network mask in bytes.*/ shift= length(size % 2**8) /*compute the size of the binary shift.*/
- = translate(#, , .) /*elide periods from IPv4 address nodes*/
$= /*initialize the to-be reassembled IPv4*/
do j=1 for max( words(#), 4) /*process each of IP node, a min of 4. */
x= word( word(#, j) 0, 1) /*use a zero for omitted IP nodes. */
if j>shift then do /*possibly elide some low─order bits. */
_= right( d2b(x), 2**5, 0) /*convert X to binary, pad with zeros.*/
x= b2d( (left(_, length(_)-shift) || left(, shift, 0) ) )
end /* [↑] "zero─out" some low─order bits*/
$= $ x /*reconstruct (by abutment) IPv4 nodes.*/
end /*j*/ /*(REXX stores it's numbers in decimal)*/
say ' original IPv4 address: ' z /*display the original IPv4 address. */ say ' canonicalized address: ' translate( space($), ., " ")mask /*canonicalized.*/ exit 0 /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ b2d: return x2d( b2x( arg(1) ) ) + 0 /*convert binary ───► decimal number.*/ d2b: return x2b( d2x( arg(1) ) ) + 0 /* " decimal ───► binary " */</lang>
- output when using the default input:
original IPv4 address: 87.70.141.1/22 canonicalized address: 87.70.140.0/22
Ruby
<lang ruby>#!/usr/bin/env ruby
- canonicalize a CIDR block: make sure none of the host bits are set
if ARGV.length == 0 then
ARGV = $stdin.readlines.map(&:chomp)
end
ARGV.each do |cidr|
# dotted-decimal / bits in network part
dotted, size_str = cidr.split('/')
size = size_str.to_i
# get IP as binary string
binary = dotted.split('.').map { |o| "%08b" % o }.join
# Replace the host part with all zeroes binary[size .. -1] = '0' * (32 - size)
# Convert back to dotted-decimal
canon = binary.chars.each_slice(8).map { |a| a.join.to_i(2) }.join('.')
# And output
puts "#{canon}/#{size}"
end</lang>
- Output:
$ canonicalize_cidr.rb 87.70.141.1/22 87.70.140.0/22
Wren
<lang ecmascript>import "os" for Process import "/fmt" for Fmt, Conv import "/str" for Str
// canonicalize a CIDR block: make sure none of the host bits are set var args = Process.arguments var cidr = (args.count > 0) ? args[0] : Fiber.abort("Please pass the CIDR to be canonicalized.")
// dotted-decimal / bits in network part var split = cidr.split("/") var dotted = split[0] var size = Num.fromString(split[1])
// get IP as binary string var binary = dotted.split(".").map { |n| Fmt.swrite("$08b", Num.fromString(n)) }.join()
// replace the host part with all zeros binary = binary[0...size] + "0" * (32 - size)
// convert back to dotted-decimal var chunks = Str.chunks(binary, 8) var canon = chunks.map { |c| Conv.atoi(c, 2) }.join(".")
// and output System.print(canon + "/" + split[1])</lang>
- Output:
$ wren canonicalize_cidr.wren 87.70.141.1/22 87.70.140.0/22