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.

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 CommonPrefix(pfx1, pfx2 netip.Prefix) (pfx netip.Prefix)
func All(first, last netip.Addr) iter.Seq[netip.Prefix]

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.

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/v4-8          12.435n ± 0%   5.099n ± 1%  -58.99% (p=0.002 n=6)
Range/v6-8          25.855n ± 0%   5.399n ± 0%  -79.12% (p=0.002 n=6)
Prefix/v4-8          16.31n ± 0%   12.07n ± 1%  -25.99% (p=0.002 n=6)
Prefix/v6-8          17.38n ± 1%   10.88n ± 1%  -37.45% (p=0.002 n=6)
CommonPrefix/v4-8    26.79n ± 0%   21.58n ± 1%  -19.43% (p=0.002 n=6)
CommonPrefix/v6-8    28.25n ± 0%   21.00n ± 1%  -25.63% (p=0.002 n=6)
geomean              20.25n        10.86n       -46.38%

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.