Function isIPv6Loopback

lib/helpers/shouldBypassProxy.js:41–70

(host)

};

const isIPv6Loopback = (host) => {
  // Collapse all-zero groups: any form of ::1 / 0:0:...:0:1
  // First, strip any leading "::" by normalising with Set lookup of common forms,
  // then fall back to structural check.
  if (host === '::1') return true;

  // Check IPv4-mapped IPv6 loopback: ::ffff:<v4-loopback> or ::ffff:<hex-v4-loopback>
  // Node's URL parser normalises ::ffff:127.0.0.1 → ::ffff:7f00:1
  const v4MappedDotted = host.match(/^::ffff:(\d+\.\d+\.\d+\.\d+)$/i);
  if (v4MappedDotted) return isIPv4Loopback(v4MappedDotted[1]);

  const v4MappedHex = host.match(/^::ffff:([0-9a-f]{1,4}):([0-9a-f]{1,4})$/i);
  if (v4MappedHex) {
    const high = parseInt(v4MappedHex[1], 16);
    // High 16 bits must start with 127 (0x7f) — i.e. 0x7f00..0x7fff
    return high >= 0x7f00 && high <= 0x7fff;
  }

  // Full-form ::1 variants: any number of zero groups followed by trailing 1
  // e.g. 0:0:0:0:0:0:0:1, 0000:...:0001
  const groups = host.split(':');
  if (groups.length === 8) {
    for (let i = 0; i < 7; i++) {
      if (!/^0+$/.test(groups[i])) return false;
    }
    return /^0*1$/.test(groups[7]);
  }

  return false;
};

const isLoopback = (host) => {
  if (!host) return false;