package extnetip

Package extnetip is an extension to the Go standard library package net/netip, providing a set of important auxiliary functions currently missing from netip for converting IP prefixes to IP ranges and vice versa.

With these extensions, it becomes straightforward to build third-party IP-range libraries based on net/netip.

API

import "github.com/gaissmai/extnetip"

func Range(p netip.Prefix) (first, last netip.Addr)
func Prefix(first, last netip.Addr) (prefix netip.Prefix, ok bool)
func All(first, last netip.Addr) iter.Seq[netip.Prefix]

Unsafe Mode

This package supports two modes of operation for converting between netip.Addr and a custom internal uint128 representation:

• When built with the unsafe build tag (e.g., go build -tags=unsafe), conversions use unsafe.Pointer to perform zero-copy, direct memory reinterpretation. This method is significantly faster.

• Without the unsafe build tag, conversions are performed safely by using binary.ByteOrder-based byte slice manipulations, avoiding use of the unsafe package. This is the default mode and is suitable when importing unsafe modules is prohibited.

Performance Benchmark

Below is a benchmark comparing the safe (default) and unsafe conversion methods:

goos: linux
goarch: amd64
pkg: github.com/gaissmai/extnetip
cpu: Intel(R) Core(TM) i5-8250U CPU @ 1.60GHz
          │   safe.bm    │             unsafe.bm              │
          │    sec/op    │   sec/op     vs base               │
Range/v4    12.980n ± 0%   5.691n ± 0%  -56.15% (p=0.002 n=6)
Range/v6    26.395n ± 0%   5.792n ± 0%  -78.06% (p=0.002 n=6)
Prefix/v4    17.17n ± 1%   12.34n ± 0%  -28.10% (p=0.002 n=6)
Prefix/v6    18.59n ± 1%   11.45n ± 0%  -38.43% (p=0.002 n=6)
geomean      18.18n        8.261n       -54.57%

Future Work

It is hoped that these frequently needed helper functions will be added to the Go standard library's netip package at some point in the future by the maintainers.

Until then, extnetip provides a robust and efficient alternative.