MAC Address Generator — C# source

// mac-address-generator — random EUI-48 MAC address generator. C# (.NET 8)
// port (canonical TS: src/lib/mac-generator.ts; Go twin:
// cli/mac-address-generator). The default rng draws from
// RandomNumberGenerator (the crypto source the TS lib uses); the showcase
// keeps the rng injectable (Func<double> returning [0, 1)) so the demo
// asserts exact MAC strings.
using System;
using System.Linq;
using System.Security.Cryptography;

record MacOptions(
    string? Separator = null,          // null -> ":"; "" concatenates
    bool Uppercase = false,
    string? Oui = null,                // 6 hex digits (separators tolerated)
    bool LocallyAdministered = false,  // force U/L bit (0x02) of the first octet
    Func<double>? Rng = null);         // null -> crypto draw in [0, 1)

static class MacGenerator
{
    static readonly Func<double> DefaultRng = () =>
        RandomNumberGenerator.GetInt32(1 << 30) / (double)(1 << 30);

    // Strip non-hex chars, require exactly 6 digits, parse the 3 OUI octets.
    static int[] ParseOui(string oui)
    {
        var clean = new string(oui.Where(Uri.IsHexDigit).ToArray());
        if (clean.Length != 6)
            throw new ArgumentException($"OUI must be 6 hex digits, got \"{oui}\"");
        return new[] { Convert.ToInt32(clean[0..2], 16), Convert.ToInt32(clean[2..4], 16), Convert.ToInt32(clean[4..6], 16) };
    }

    // Build a random EUI-48 MAC: 3 OUI octets (given or random) + 3 random,
    // U/L bit forced when asked, joined as %02x with the separator.
    public static string Generate(MacOptions? o = null)
    {
        o ??= new MacOptions();
        var rng = o.Rng ?? DefaultRng;
        var oct = o.Oui is { Length: > 0 }
            ? ParseOui(o.Oui)
            : Enumerable.Range(0, 3).Select(_ => (int)(rng() * 256)).ToArray();
        oct = oct.Concat(Enumerable.Range(0, 3).Select(_ => (int)(rng() * 256))).ToArray();
        if (o.LocallyAdministered) oct[0] = (oct[0] & 0xFD) | 0x02;
        var mac = string.Join(o.Separator ?? ":", oct.Select(b => b.ToString("x2")));
        return o.Uppercase ? mac.ToUpperInvariant() : mac;
    }
}

class Demo
{
    static void Main()
    {
        Console.WriteLine(MacGenerator.Generate(new(Rng: () => 0)));                          // 00:00:00:00:00:00
        Console.WriteLine(MacGenerator.Generate(new(Separator: "-")));                        // 6 random pairs, dash-joined
        Console.WriteLine(MacGenerator.Generate(new(Rng: () => 0.7, Uppercase: true)));       // B3:B3:B3:B3:B3:B3
        Console.WriteLine(MacGenerator.Generate(new(Rng: () => 0, Oui: "aa-bb-cc")));         // aa:bb:cc:00:00:00
        Console.WriteLine(MacGenerator.Generate(new(Rng: () => 0.5, LocallyAdministered: true))); // 82:80:80:80:80:80
    }
}