Function expandIPv6Groups

src/utils/hooks/ssrfGuard.ts:133–179

* Expand `::` and optional trailing dotted-decimal so an IPv6 address is * represented as exactly 8 hex groups. Returns null if expansion is not * well-formed (the caller has already validated with isIP, so this is * defensive).

(addr: string)

 * defensive).
 */
function expandIPv6Groups(addr: string): number[] | null {
  // Handle trailing dotted-decimal IPv4 (e.g. ::ffff:169.254.169.254).
  // Replace it with its two hex groups so the rest of the expansion is uniform.
  let tailHextets: number[] = []
  if (addr.includes('.')) {
    const lastColon = addr.lastIndexOf(':')
    const v4 = addr.slice(lastColon + 1)
    addr = addr.slice(0, lastColon)
    const octets = v4.split('.').map(Number)
    if (
      octets.length !== 4 ||
      octets.some(n => !Number.isInteger(n) || n < 0 || n > 255)
    ) {
      return null
    }
    tailHextets = [
      (octets[0]! << 8) | octets[1]!,
      (octets[2]! << 8) | octets[3]!,
    ]
  }

  // Expand `::` (at most one) into the right number of zero groups.
  const dbl = addr.indexOf('::')
  let head: string[]
  let tail: string[]
  if (dbl === -1) {
    head = addr.split(':')
    tail = []
  } else {
    const headStr = addr.slice(0, dbl)
    const tailStr = addr.slice(dbl + 2)
    head = headStr === '' ? [] : headStr.split(':')
    tail = tailStr === '' ? [] : tailStr.split(':')
  }

  const target = 8 - tailHextets.length
  const fill = target - head.length - tail.length
  if (fill < 0) return null

  const hex = [...head, ...new Array<string>(fill).fill('0'), ...tail]
  const nums = hex.map(h => parseInt(h, 16))
  if (nums.some(n => Number.isNaN(n) || n < 0 || n > 0xffff)) {
    return null
  }
  nums.push(...tailHextets)
  return nums.length === 8 ? nums : null
}

/**
 * Extract the embedded IPv4 address from an IPv4-mapped IPv6 address