private static void ApplyCipher(Span <byte> packetData, byte[] cipher, bool encrypt)
{
if (cipher.Length != RequiredLength)
{
throw new ArgumentException($"The cipher size must be {RequiredLength}, but is {cipher.Length}", nameof(cipher));
}
var packet = new PacketView(packetData);
if (packet.IsPartial)
{
throw new ArgumentException("Refusing to apply XOR cipher to partial packet", nameof(packet));
}
if (packet.Type.IsEncrypted)
{
throw new ArgumentException("Refusing to apply XOR cipher to encrypted packet", nameof(packet));
}
int start = encrypt ? packet.Type.HeaderLength + 1 : packet.Length - 1;
int end = encrypt ? packet.Length : packet.Type.HeaderLength;
for (int i = start; i != end; i += encrypt ? 1 : -1)
{
packetData[i] ^= (byte)(packet.Data[i - 1] ^ cipher[i % cipher.Length]);
}
}
/// <summary>Throws an exception if the packet header does not match.</summary>
public void EnsureMatchingHeader(Span <byte> data, int minimumPayloadSize)
{
var packet = new PacketView(data);
if (!packet.HasIdentifier(this.Identifier))
{
// TODO: Specialized exception
throw new ArgumentException(nameof(data));
}
if (packet.Length < this.PayloadOffset + minimumPayloadSize)
{
// TODO: Specialized exception
throw new ArgumentOutOfRangeException(nameof(data));
}
if (packet.Length != this.Type.ReadSize(data))
{
// TODO: Specialized exception
throw new ArgumentException(nameof(data));
}
}