Add IPv4 CIDR four-part decimal validator

Author: toof-jp

README.md

@@ -127,6 +127,7 @@ The `ipaddr.IPv4` and `ipaddr.IPv6` objects have some methods defined, too. All
 `ipaddr.IPvX.isValid(string)` can be used to check if the string is a valid address for particular protocol, and `ipaddr.IPvX.parse(string)` is the error-throwing parser.
 
 `ipaddr.IPvX.isValid(string)` uses the same format for parsing as the POSIX `inet_ntoa` function, which accepts unusual formats like `0xc0.168.1.1` or `0x10000000`. The function `ipaddr.IPv4.isValidFourPartDecimal(string)` validates the IPv4 address and also ensures that it is written in four-part decimal format.
+`ipaddr.IPv4.isValidCIDRFourPartDecimal(string)` validates an IPv4 address in CIDR notation and also ensures that its address portion is written in four-part decimal format.
 
 [IPv6 ranges]: https://github.com/whitequark/ipaddr.js/blob/master/lib/ipaddr.js#L530
 [IPv4 ranges]: https://github.com/whitequark/ipaddr.js/blob/master/lib/ipaddr.js#L182

lib/ipaddr.js

@@ -365,6 +365,17 @@
         }
     };
 
+    // Checks if a given string is a full four-part IPv4 Address with CIDR prefix.
+    ipaddr.IPv4.isValidCIDRFourPartDecimal = function (string) {
+        const match = string.match(/^(.+)\/(\d+)$/);
+
+        if (!ipaddr.IPv4.isValidCIDR(string) || !match) {
+            return false;
+        }
+
+        return ipaddr.IPv4.isValidFourPartDecimal(match[1]);
+    };
+
     // A utility function to return network address given the IPv4 interface and prefix length in CIDR notation
     ipaddr.IPv4.networkAddressFromCIDR = function (string) {
         let cidr, i, ipInterfaceOctets, octets, subnetMaskOctets;

lib/ipaddr.js.d.ts

@@ -30,6 +30,7 @@ declare module "ipaddr.js" {
             static isValid(addr: string): boolean;
             static isValidCIDR(addr: string): boolean;
             static isValidFourPartDecimal(addr: string): boolean;
+            static isValidCIDRFourPartDecimal(addr: string): boolean;
             static networkAddressFromCIDR(addr: string): IPv4;
             static parse(addr: string): IPv4;
             static parseCIDR(addr: string): [IPv4, number];

test/ipaddr.test.js

@@ -160,6 +160,14 @@ describe('ipaddr', () => {
         assert.equal(ipaddr.IPv4.isValidFourPartDecimal('0xc0.168.1.1'), false);
     })
 
+    it('checks the conventional IPv4 CIDR format', () => {
+        assert.equal(ipaddr.IPv4.isValidCIDRFourPartDecimal('192.168.1.1/24'), true);
+        assert.equal(ipaddr.IPv4.isValidCIDRFourPartDecimal('0.0.0.0/0'), true);
+        assert.equal(ipaddr.IPv4.isValidCIDRFourPartDecimal('0xc0.168.1.1/24'), false);
+        assert.equal(ipaddr.IPv4.isValidCIDRFourPartDecimal('192.168.1.1/33'), false);
+        assert.equal(ipaddr.IPv4.isValidCIDRFourPartDecimal('192.168.1/24'), false);
+    })
+
     it('refuses to construct IPv4 address with trailing and leading zeros', () => {
         assert.equal(ipaddr.IPv4.isValidFourPartDecimal('000000192.168.100.2'), false);
         assert.equal(ipaddr.IPv4.isValidFourPartDecimal('192.0000168.100.2'), false);