Rendezvous/tests/FinalFactory.Rendezvous.Tests/Contracts/UdpCodecTests.cs

using FinalFactory.Rendezvous.Contracts;

namespace FinalFactory.Rendezvous.Tests.Contracts;

public sealed class UdpCodecTests
{
    private static readonly Guid Handle = new("00112233-4455-6677-8899-aabbccddeeff");

    [Fact]
    public void HostPresenceMatchesTheV1GoldenVector()
    {
        byte[] encoded = RendezvousUdpCodec.Encode(CreateDatagram());

        Assert.Equal(ContractTestFiles.Read("udp-host-ipv4.hex"), Convert.ToHexString(encoded).ToLowerInvariant());
        Assert.True(RendezvousUdpCodec.TryDecode(encoded, out PresenceDatagram? decoded, out UdpDecodeError error));
        Assert.Equal(UdpDecodeError.None, error);
        Assert.NotNull(decoded);
        Assert.Equal(Handle, decoded.MediationHandle.Value);
        Assert.Equal("192.0.2.10", decoded.LocalAddress);
        Assert.Equal(9050, decoded.LocalPort);
        Assert.Equal("Abc_123-xYz", decoded.Capability);
    }

    [Fact]
    public void Ipv6RoundtripsWithoutLosingItsAddressFamily()
    {
        PresenceDatagram original = CreateDatagram();
        original.MessageType = UdpPresenceMessageType.ClientPresence;
        original.AddressFamily = AddressFamilyKind.Ipv6;
        original.LocalAddress = "2001:db8::10";

        byte[] encoded = RendezvousUdpCodec.Encode(original);

        Assert.True(RendezvousUdpCodec.TryDecode(encoded, out PresenceDatagram? decoded, out _));
        Assert.NotNull(decoded);
        Assert.Equal(AddressFamilyKind.Ipv6, decoded.AddressFamily);
        Assert.Equal("2001:db8::10", decoded.LocalAddress);
    }

    [Fact]
    public void EncoderRejectsAnAddressFamilyMismatch()
    {
        PresenceDatagram datagram = CreateDatagram();
        datagram.AddressFamily = AddressFamilyKind.Ipv4;
        datagram.LocalAddress = "2001:db8::10";

        Assert.Throws<ArgumentException>(() => RendezvousUdpCodec.Encode(datagram));
    }

    [Theory]
    [InlineData(2, 2, UdpDecodeError.UnsupportedVersion)]
    [InlineData(3, 3, UdpDecodeError.UnknownMessageType)]
    [InlineData(4, 1, UdpDecodeError.InvalidFlags)]
    [InlineData(21, 5, UdpDecodeError.InvalidAddressFamily)]
    public void DecoderReturnsStableErrorsForUnknownHeaderValues(
        int offset,
        byte replacement,
        UdpDecodeError expected)
    {
        byte[] encoded = RendezvousUdpCodec.Encode(CreateDatagram());
        encoded[offset] = replacement;

        Assert.False(RendezvousUdpCodec.TryDecode(encoded, out _, out UdpDecodeError actual));
        Assert.Equal(expected, actual);
    }

    [Fact]
    public void DecoderRejectsTruncationTrailingDataAndOversizedPackets()
    {
        byte[] encoded = RendezvousUdpCodec.Encode(CreateDatagram());
        byte[] trailing = [.. encoded, 0];
        byte[] oversized = new byte[ContractLimits.UdpDatagramMaxBytes + 1];

        Assert.False(RendezvousUdpCodec.TryDecode(encoded.AsSpan(0, encoded.Length - 1), out _, out UdpDecodeError truncated));
        Assert.Equal(UdpDecodeError.Truncated, truncated);
        Assert.False(RendezvousUdpCodec.TryDecode(trailing, out _, out UdpDecodeError trailingError));
        Assert.Equal(UdpDecodeError.TrailingData, trailingError);
        Assert.False(RendezvousUdpCodec.TryDecode(oversized, out _, out UdpDecodeError oversizedError));
        Assert.Equal(UdpDecodeError.DatagramTooLarge, oversizedError);
    }

    [Fact]
    public void DecoderRejectsNonBase64UrlCapabilities()
    {
        byte[] encoded = RendezvousUdpCodec.Encode(CreateDatagram());
        encoded[^1] = (byte)'+';

        Assert.False(RendezvousUdpCodec.TryDecode(encoded, out _, out UdpDecodeError error));
        Assert.Equal(UdpDecodeError.InvalidCapability, error);
    }

    private static PresenceDatagram CreateDatagram() => new()
    {
        MessageType = UdpPresenceMessageType.HostPresence,
        MediationHandle = new MediationHandle(Handle),
        AddressFamily = AddressFamilyKind.Ipv4,
        LocalAddress = "192.0.2.10",
        LocalPort = 9050,
        Capability = "Abc_123-xYz",
    };
}