static int Main(string[] args)
{
if (args.Length < 1)
{
Console.WriteLine(PuzzleFileFns.StandardOneParamRequiredErrorMessage);
return(1);
}
var allLines = File.ReadAllLines(args[0]);
int payloadStartLine = PuzzleFileFns.GetLinePayloadStartsAt(allLines);
var payload = PuzzleFileFns.GetPayloadAsOneLongString(allLines, payloadStartLine);
Debug.Assert(payload.StartsWith("<~70!<j!!#7a+;"));
Debug.Assert(payload.EndsWith(":j*\"<<*=Q1C=~>"));
Debug.Assert(payload.Contains("\n") == false);
var ipv4PacketsSpan = Ascii85Fns.DecodeAsSpan(payload, 2);
var packetStream = new MemoryStream(ipv4PacketsSpan.ToArray());
var memBuffer = new MemoryStream();
foreach (var ipv4Frame in IPv4Fns.IterateFrames(packetStream))
{
if (!ipv4Frame.Header.ChecksumOK)
{
continue;
}
var udpFrame = UDPFns.DecodeUDP(ipv4Frame.Data);
if (!PacketFilter(ipv4Frame.Header, udpFrame))
{
continue;
}
memBuffer.Write(udpFrame.Data, 0, udpFrame.Data.Length);
}
// Debugging:
// var ipv4frame = IPv4Fns.IterateFrames(payloadStream).Last();
// System.Console.WriteLine(
// UDPFns.UDPToDebugString(
// ipv4frame.Header.SourceAddress,
// ipv4frame.Header.DestinationAddress,
// UDPFns.DecodeUDP(ipv4frame.Data)));
// var udpPacket = UDPFns.DecodeUDP(ipv4frame.Data);
// var checksum = UDPFns.UDPChecksum(ipv4frame.Header.SourceAddress, ipv4frame.Header.DestinationAddress, udpPacket);
// System.Console.WriteLine("Checksum (calc)={0:x4}", checksum);
memBuffer.Position = 0L;
Console.WriteLine(Encoding.ASCII.GetString(memBuffer.ToArray()));
return(0);
}
static bool PacketFilter(IPv4Header ipv4Header, UDPFrame udpFrame)
{
if (ipv4Header.ChecksumOK == false ||
!ipv4Header.SourceAddress.Equals(FilterSourceAddr) ||
!ipv4Header.DestinationAddress.Equals(FilterDestAddr) ||
udpFrame.Header.DestinationPort != FilterDestPort)
{
return(false);
}
return(UDPFns.UDPChecksum(ipv4Header.SourceAddress, ipv4Header.DestinationAddress, udpFrame) == udpFrame.Header.Checksum);
}
