/// <summary>
/// Requests PIT for the specified block from a random connected neighbor node.
/// Nominally, only the transactions included in `txids` need to be verifiable with the PIT, but
/// due to how Cuckoo filtering works, some false positives will also be included. This helps with anonymization, if the false positive rate is high enough.
/// </summary>
/// <param name="block_num">Block number for which the PIT should be included.</param>
/// <param name="txids">List of interesting transactions, which we wish to verify.</param>
private void requestPITForBlock(ulong block_num, List <string> txids)
{
lock (pitCache)
{
long currentTime = Clock.getTimestamp();
// Request might already have been sent. In that case, we re-send it we have been waiting for too long.
if (!pitCache.ContainsKey(block_num) || currentTime - pitCache[block_num].requestSent > pitRequestTimeout)
{
Cuckoo filter = new Cuckoo(txids.Count);
foreach (var tx in txids)
{
filter.Add(Encoding.UTF8.GetBytes(tx));
}
byte[] filter_bytes = filter.getFilterBytes();
MemoryStream m = new MemoryStream(filter_bytes.Length + 12);
using (BinaryWriter w = new BinaryWriter(m, Encoding.UTF8, true))
{
w.Write(block_num);
w.Write(filter_bytes.Length);
w.Write(filter_bytes);
}
CoreProtocolMessage.broadcastProtocolMessageToSingleRandomNode(new char[] { 'M' }, ProtocolMessageCode.getPIT, m.ToArray(), 0);
PITCacheItem ci = new PITCacheItem()
{
pit = null,
requestedForTXIDs = txids,
requestSent = Clock.getTimestamp()
};
pitCache.AddOrReplace(block_num, ci);
}
}
}
