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Validate And Classify IPv4 Addresses

Parse dotted-quad IPv4 addresses strictly, reject leading zeros, and classify private, loopback and link-local ranges.

JavascriptForm Validation

Code

snippet
export function parseIPv4(address) {
  if (typeof address !== "string") return null;
  const parts = address.split(".");
  if (parts.length !== 4) return null;
  const octets = [];
  for (const part of parts) {
    if (!/^\d{1,3}$/.test(part)) return null;
    if (part.length > 1 && part.startsWith("0")) return null;
    const value = Number(part);
    if (value > 255) return null;
    octets.push(value);
  }
  return octets;
}

export function isValidIPv4(address) {
  return parseIPv4(address) !== null;
}

export function isPrivateIPv4(address) {
  const octets = parseIPv4(address);
  if (!octets) return false;
  const [a, b] = octets;
  return a === 10
    || (a === 172 && b >= 16 && b <= 31)
    || (a === 192 && b === 168)
    || a === 127
    || (a === 169 && b === 254);
}

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