Go's net.ParseIP in TypeScript

✓ Verified: Go 1.23

How to use

Install via yarn add locutus and import: import { ParseIP } from 'locutus/golang/net/ParseIP'.

Or with CommonJS: const { ParseIP } = require('locutus/golang/net/ParseIP')

Use a bundler that supports tree-shaking so you only ship the functions you actually use. Vite, webpack, Rollup, and Parcel all handle this. For server-side use this is less of a concern.

Examples

These examples are extracted from test cases that automatically verify our functions against their native counterparts.

#	code	expected result
1	`ParseIP('127.0.0.1')`	`'127.0.0.1'`
2	`ParseIP('2001:DB8::1')`	`'2001:db8::1'`
3	`ParseIP('999.1.2.3')`	`null`

Notes

Parses IPv4/IPv6 textual addresses and returns a normalized string or null when invalid.
IPv6 output is normalized to lowercase but not fully canonicalized.

Here's what our current TypeScript equivalent to Go's net.ParseIP looks like.

type IPv4Bytes = [number, number, number, number]

export function ParseIP(value: string): string | null {
  //      discuss at: https://locutus.io/golang/net/ParseIP/
  // parity verified: Go 1.23
  //     original by: Kevin van Zonneveld (https://kvz.io)
  //          note 1: Parses IPv4/IPv6 textual addresses and returns a normalized string or null when invalid.
  //          note 2: IPv6 output is normalized to lowercase but not fully canonicalized.
  //       example 1: ParseIP('127.0.0.1')
  //       returns 1: '127.0.0.1'
  //       example 2: ParseIP('2001:DB8::1')
  //       returns 2: '2001:db8::1'
  //       example 3: ParseIP('999.1.2.3')
  //       returns 3: null

  const input = String(value)
  const ipv4 = parseIPv4(input)
  if (ipv4) {
    return ipv4.join('.')
  }

  if (isValidIPv6(input)) {
    return input.toLowerCase()
  }

  return null
}

function parseIPv4(value: string): IPv4Bytes | null {
  const parts = value.split('.')
  if (parts.length !== 4) {
    return null
  }

  const bytes: number[] = []
  for (const part of parts) {
    if (!/^\d+$/.test(part)) {
      return null
    }
    if (part.length > 1 && part.startsWith('0')) {
      return null
    }
    const n = Number(part)
    if (!Number.isInteger(n) || n < 0 || n > 255) {
      return null
    }
    bytes.push(n)
  }

  return [bytes[0] ?? 0, bytes[1] ?? 0, bytes[2] ?? 0, bytes[3] ?? 0]
}

function isValidIPv6(value: string): boolean {
  if (value === '' || value.includes('[') || value.includes(']') || value.includes('%')) {
    return false
  }

  const doubleColonParts = value.split('::')
  if (doubleColonParts.length > 2) {
    return false
  }

  const hasCompression = doubleColonParts.length === 2
  const left = doubleColonParts[0] ?? ''
  const right = doubleColonParts[1] ?? ''

  const leftGroups = left === '' ? [] : left.split(':')
  const rightGroups = right === '' ? [] : right.split(':')

  if (leftGroups.some((group) => group === '') || rightGroups.some((group) => group === '')) {
    return false
  }

  let groupCount = 0

  for (let i = 0; i < leftGroups.length; i++) {
    const group = leftGroups[i] ?? ''
    if (group.includes('.')) {
      if (i !== leftGroups.length - 1 || rightGroups.length > 0) {
        return false
      }
      if (!parseIPv4(group)) {
        return false
      }
      groupCount += 2
      continue
    }

    if (!isValidHextet(group)) {
      return false
    }
    groupCount += 1
  }

  for (let i = 0; i < rightGroups.length; i++) {
    const group = rightGroups[i] ?? ''
    if (group.includes('.')) {
      if (i !== rightGroups.length - 1) {
        return false
      }
      if (!parseIPv4(group)) {
        return false
      }
      groupCount += 2
      continue
    }

    if (!isValidHextet(group)) {
      return false
    }
    groupCount += 1
  }

  if (hasCompression) {
    return groupCount < 8
  }

  return groupCount === 8
}

function isValidHextet(value: string): boolean {
  return /^[0-9a-fA-F]{1,4}$/.test(value)
}

Improve this function

Locutus is a community effort following The McDonald's Theory: we ship first iterations, hoping others will improve them. If you see something that could be better, we'd love your contribution.

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Help us add more

Got a rainy Sunday afternoon and a taste for a porting puzzle?

Get inspiration from Go strings documentation, Go strings source, Go strings examples source, GopherJS.
Click "New file" in the appropriate folder on GitHub. This will fork the project to your account, directly add the file to it, and send a Pull Request to us.

We will then review it. If it's useful to the project and in line with our contributing guidelines your work will become part of Locutus and you'll be automatically credited in the authors section accordingly.

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