Groovy code to fetch all available IP address from a given subnet denoted with CIDR notation

Question

I have generated the below code with the help of Gen AI, but its returning a empty list. Can someone help me to debug this?

static List<String> generateAvailableIps(String subnetCidr) {
    // Parse the CIDR notation
    def (ipAddress, subnetMask) = subnetCidr.split("/")

    // Convert IP address to integer
    def ipInt = ipAddress.split("\\.").inject(0) { acc, value -> (acc << 8) + value.toInteger() }

    // Get subnet mask as integer
    def subnetMaskInt = (1 << (32 - subnetMask.toInteger())) - 1

    // Get network address
    def networkAddress = ipInt & subnetMaskInt

    // Get first and last usable IP addresses (excluding network and broadcast)
    def firstUsableIp = networkAddress + 1
    def broadcastAddress = networkAddress | ~subnetMaskInt
    def lastUsableIp = broadcastAddress - 1

    // Generate a list of available IP addresses
    def availableIps = []
    for (int i = firstUsableIp; i <= lastUsableIp; i++) {
        def octet1 = (i >> 24) & 0xff
        def octet2 = (i >> 16) & 0xff
        def octet3 = (i >> 8) & 0xff
        def octet4 = i & 0xff
        availableIps.add("$octet1.$octet2.$octet3.$octet4")
    }

    return availableIps
}

// Example usage
def availableIps = generateAvailableIps("192.168.35.32/27")
println(availableIps)

List of IP addresses available from a given subnet

Answer 1

static List<String> generateAvailableIps(String subnetCidr) {
    // Parse the CIDR notation
    def (ipAddress, subnetMask) = subnetCidr.split("/")

    // Convert IP address to integer
    def ipInt = ipAddress.split("\\.").inject(0) { acc, value -> (acc << 8) + value.toInteger() }

    // Get subnet mask as integer
    def subnetMaskInt = (-1 << (32 - subnetMask.toInteger()))
 
    // Get network address
    def networkAddress = ipInt & subnetMaskInt
  
    // Get first and last usable IP addresses (excluding network and broadcast)
    def broadcastAddress = networkAddress | ~subnetMaskInt
    def firstUsableIp = ""
    def lastUsableIp = ""
     
    if(subnetMask != "31")
    {
        firstUsableIp = networkAddress + 1
        lastUsableIp = broadcastAddress - 1
    }
    else
    {
        firstUsableIp = networkAddress
        lastUsableIp = broadcastAddress 
    }
    
    // Generate a list of available IP addresses
    def availableIps = []
    for (int i = firstUsableIp; i <= lastUsableIp; i++) {
        def octet1 = (i >> 24) & 0xff
        def octet2 = (i >> 16) & 0xff
        def octet3 = (i >> 8) & 0xff
        def octet4 = i & 0xff
        availableIps.add("$octet1.$octet2.$octet3.$octet4")
    }

    return availableIps
}

// Example usage
def subnetCidrs = ["192.168.0.0/31","192.168.35.32/27"]
def String ipAddress = '192.168.35.37'

for (subnetCidr in subnetCidrs) {
    def availableIps = generateAvailableIps(subnetCidr)
    println(availableIps)  
}