private bool Validate(byte[] data, int msgLength)
{
// do we have enough data in the buffer for a HashCash token?
if (msgLength < Kcp.OVERHEAD + KcpConnection.RESERVED + HashCashEncoding.SIZE)
{
return(false);
}
// read the token
HashCash token = HashCashEncoding.Decode(data, Kcp.OVERHEAD + KcpConnection.RESERVED);
RemoveExpiredTokens();
// have this token been used?
if (used.Contains(token))
{
return(false);
}
// does the token validate?
if (!token.Validate("Application.productName", HashCashBits))
{
return(false);
}
used.Add(token);
expireQueue.Enqueue(token);
// brand new token, and it is for this app, go on
return(true);
}
protected async UniTask HandshakeAsync(int bits)
{
// in the very first message we must mine a hashcash token
// and send that as a hello
// the server won't accept connections otherwise
string applicationName = Application.productName;
HashCash token = await UniTask.RunOnThreadPool(() => HashCash.Mine(applicationName, bits));
byte[] hello = new byte[1000];
int length = HashCashEncoding.Encode(hello, 0, token);
var data = new ArraySegment <byte>(hello, 0, length);
// send a greeting and see if the server replies
await SendAsync(data);
var stream = new MemoryStream();
try
{
await ReceiveAsync(stream);
}
catch (Exception e)
{
throw new InvalidDataException("Unable to establish connection, no Handshake message received.", e);
}
}
/// <summary>
/// Encode a hashcash token into a buffer
/// </summary>
/// <param name="buffer">the buffer where to store the hashcash</param>
/// <param name="index">the index in the buffer where to put it</param>
/// <param name="hashCash">the token to be encoded</param>
/// <returns>the length of the written data</returns>
public static int Encode(byte[] buffer, int index, HashCash hashCash)
{
var encoder = new Encoder(buffer, index);
encoder.Encode64U((ulong)hashCash.dt.Ticks);
encoder.Encode32U((uint)hashCash.resource);
encoder.Encode64U(hashCash.salt);
encoder.Encode64U(hashCash.counter);
return(encoder.Position - index);
}
// remove all the tokens that expired
private void RemoveExpiredTokens()
{
DateTime threshold = DateTime.UtcNow.AddMinutes(-10);
while (expireQueue.Count > 0)
{
HashCash token = expireQueue.Peek();
if (token.dt > threshold)
{
return;
}
expireQueue.Dequeue();
used.Remove(token);
}
}
/// <summary>
/// Encode a hashcash token into a buffer
/// </summary>
/// <param name="buffer">the buffer where to store the hashcash</param>
/// <param name="index">the index in the buffer where to put it</param>
/// <param name="hashCash">the token to be encoded</param>
/// <returns>the length of the written data</returns>
public static HashCash Decode(byte[] buffer, int index)
{
var decoder = new Decoder(buffer, index);
long ticks = (long)decoder.Decode64U();
int resource = (int)decoder.Decode32U();
ulong salt = decoder.Decode64U();
ulong counter = decoder.Decode64U();
var token = new HashCash(
new DateTime(ticks),
resource,
salt,
counter
);
return(token);
}