namespace gatuna; using System.Text; static class Proto { public const ushort EtherType = 0x6969; public const int EthHeaderLen = 14; public const byte Version = 1; public const int HeaderLen = 8; public const int MaxPayload = 1480; public const byte TypeDiscover = 0x01; public const byte TypeManifest = 0x02; public const byte TypeOpen = 0x03; public const byte TypeOpenAck = 0x04; public const byte TypeOpenNak = 0x05; public const byte TypeData = 0x06; public const byte TypeClose = 0x07; public const byte TypePing = 0x0B; public const byte TypePong = 0x0C; public const byte ProtoTcp = 1; public const byte ProtoUdp = 2; public const byte ReasonUnspecified = 0; public const byte ReasonUnknownUpstream = 1; public const byte ReasonConnectFailed = 2; public const byte ReasonOversize = 3; public const byte ReasonUnknownSession = 4; } readonly record struct UpstreamEntry( byte Id, byte Protocol, ushort Port, string? Label) { public string ProtoName => Protocol == Proto.ProtoTcp ? "tcp" : "udp"; } abstract record Frame { internal record Discover : Frame; internal record Manifest(string Hostname, UpstreamEntry[] Entries) : Frame; internal record Open(byte UpstreamId) : Frame; internal record OpenAck(uint SessionId, byte UpstreamId) : Frame; internal record OpenNak(byte UpstreamId, byte Reason) : Frame; internal record Data(uint SessionId, byte[] Payload) : Frame; internal record Close(uint SessionId, byte? Reason) : Frame; internal record Ping(ulong Nonce) : Frame; internal record Pong(ulong Nonce) : Frame; } static class FrameCodec { /// Build the 8-byte header + payload. payload_len records the exact /// payload length so the receiver can ignore Ethernet padding. static byte[] Build(byte type, uint sessionId, byte[] payload) { var buf = new byte[Proto.HeaderLen + payload.Length]; buf[0] = Proto.Version; buf[1] = type; buf[2] = (byte)(sessionId >> 24); buf[3] = (byte)(sessionId >> 16); buf[4] = (byte)(sessionId >> 8); buf[5] = (byte)(sessionId & 0xFF); buf[6] = (byte)(payload.Length >> 8); buf[7] = (byte)(payload.Length & 0xFF); Buffer.BlockCopy(payload, 0, buf, Proto.HeaderLen, payload.Length); return buf; } public static byte[] Encode(Frame frame) { return frame switch { Frame.Discover => Build(Proto.TypeDiscover, 0, []), Frame.Manifest manifest => Build(Proto.TypeManifest, 0, BuildManifestPayload(manifest.Hostname, manifest.Entries)), Frame.Open open => Build(Proto.TypeOpen, 0, [open.UpstreamId]), Frame.OpenAck ack => Build(Proto.TypeOpenAck, ack.SessionId, [ack.UpstreamId]), Frame.OpenNak nak => Build(Proto.TypeOpenNak, 0, [nak.UpstreamId, nak.Reason]), Frame.Data data => Build(Proto.TypeData, data.SessionId, data.Payload), Frame.Close close => Build(Proto.TypeClose, close.SessionId, close.Reason.HasValue ? [close.Reason.Value] : []), Frame.Ping ping => Build(Proto.TypePing, 0, EncodeNonce(ping.Nonce)), Frame.Pong pong => Build(Proto.TypePong, 0, EncodeNonce(pong.Nonce)), _ => throw new InvalidOperationException($"unknown frame type: {frame.GetType()}"), }; } static byte[] BuildManifestPayload(string hostname, UpstreamEntry[] entries) { using var ms = new MemoryStream(); var hnBytes = Encoding.UTF8.GetBytes(hostname); var hnLen = (byte)Math.Min(hnBytes.Length, 255); ms.WriteByte(hnLen); if (hnLen > 0) ms.Write(hnBytes, 0, hnLen); foreach (var e in entries) { var labelBytes = Encoding.UTF8.GetBytes(e.Label ?? ""); var labelLen = (byte)Math.Min(labelBytes.Length, 255); ms.WriteByte(e.Id); ms.WriteByte(e.Protocol); ms.WriteByte((byte)(e.Port >> 8)); ms.WriteByte((byte)(e.Port & 0xFF)); ms.WriteByte(labelLen); if (labelLen > 0) ms.Write(labelBytes, 0, labelLen); } return ms.ToArray(); } public static Frame? Parse(ReadOnlySpan buf) { if (buf.Length < Proto.HeaderLen) return null; if (buf[0] != Proto.Version) return null; var type = buf[1]; var sessionId = (uint)(buf[2] << 24 | buf[3] << 16 | buf[4] << 8 | buf[5]); var payloadLen = (ushort)(buf[6] << 8 | buf[7]); if (buf.Length < Proto.HeaderLen + payloadLen) return null; // Slice exactly payloadLen bytes, ignoring any trailing Ethernet padding. var payload = buf.Slice(Proto.HeaderLen, payloadLen); return type switch { Proto.TypeManifest => ParseManifest(payload), Proto.TypeOpenAck when payload.Length == 1 => new Frame.OpenAck(sessionId, payload[0]), Proto.TypeOpenNak when payload.Length == 2 => new Frame.OpenNak(payload[0], payload[1]), Proto.TypeData when payload.Length <= Proto.MaxPayload => new Frame.Data(sessionId, payload.ToArray()), Proto.TypeClose when payload.Length is 0 or 1 => new Frame.Close(sessionId, payload.Length == 1 ? payload[0] : null), Proto.TypePong when payload.Length == 8 => new Frame.Pong(ParseNonce(payload)), Proto.TypePing when payload.Length == 8 => new Frame.Ping(ParseNonce(payload)), Proto.TypeDiscover when payload.Length == 0 => new Frame.Discover(), _ => null, }; } static ulong ParseNonce(ReadOnlySpan payload) { ulong nonce = 0; for (int i = 0; i < 8; i++) nonce = (nonce << 8) | payload[i]; return nonce; } static byte[] EncodeNonce(ulong nonce) { return [ (byte)(nonce >> 56), (byte)(nonce >> 48), (byte)(nonce >> 40), (byte)(nonce >> 32), (byte)(nonce >> 24), (byte)(nonce >> 16), (byte)(nonce >> 8), (byte)(nonce & 0xFF), ]; } static Frame.Manifest? ParseManifest(ReadOnlySpan payload) { if (payload.Length < 1) return null; var hnLen = payload[0]; if (1 + hnLen > payload.Length) return null; var hostname = hnLen == 0 ? "" : Encoding.UTF8.GetString(payload[1..(1 + hnLen)]); var rest = payload[(1 + hnLen)..]; var entries = new List(); int i = 0; while (i < rest.Length) { if (i + 5 > rest.Length) return null; var id = rest[i]; var proto = rest[i + 1]; var port = (ushort)(rest[i + 2] << 8 | rest[i + 3]); var labelLen = rest[i + 4]; i += 5; if (i + labelLen > rest.Length) return null; string? label = labelLen == 0 ? null : Encoding.UTF8.GetString(rest[i..(i + labelLen)]); i += labelLen; entries.Add(new UpstreamEntry(id, proto, port, label)); } return new Frame.Manifest(hostname, entries.ToArray()); } }