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add payload_len field to wire protocol header

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Ethernet pads frames to 60 bytes minimum; without an explicit length
field the receiver cannot distinguish real payload from zero padding
(e.g. a 6-byte DISCOVER becomes 46 bytes after padding, failing the
'payload must be empty' check).

Header is now 8 bytes: [ver:1][type:1][session_id:4][payload_len:2]
(both multi-byte fields big-endian). The receiver slices exactly
payload_len bytes and ignores trailing padding.

Updated PROTOCOL.md, Rust frame.rs, and C# Frame.cs.
This commit is contained in:
Mute
2026-08-13 07:51:39 +00:00
parent dc5df5c073
commit f09028b135
3 changed files with 78 additions and 57 deletions
Download Patch File Download Diff File Expand all files Collapse all files
win/gatuna-client/Frame.cs
+33 -24
View File
@@ -7,6 +7,7 @@ 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;
@@ -49,34 +50,49 @@ abstract record 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 =>
Header(Proto.TypeDiscover, 0),
Build(Proto.TypeDiscover, 0, []),
Frame.Manifest manifest =>
BuildManifest(manifest.Entries),
Build(Proto.TypeManifest, 0, BuildManifestPayload(manifest.Entries)),
Frame.Open open =>
[.. Header(Proto.TypeOpen, 0), open.UpstreamId],
Build(Proto.TypeOpen, 0, [open.UpstreamId]),
Frame.OpenAck ack =>
[.. Header(Proto.TypeOpenAck, ack.SessionId), ack.UpstreamId],
Build(Proto.TypeOpenAck, ack.SessionId, [ack.UpstreamId]),
Frame.OpenNak nak =>
[.. Header(Proto.TypeOpenNak, 0), nak.UpstreamId, nak.Reason],
Build(Proto.TypeOpenNak, 0, [nak.UpstreamId, nak.Reason]),
Frame.Data data =>
[.. Header(Proto.TypeData, data.SessionId), .. data.Payload],
Build(Proto.TypeData, data.SessionId, data.Payload),
Frame.Close close =>
close.Reason.HasValue
? [.. Header(Proto.TypeClose, close.SessionId), close.Reason.Value]
: Header(Proto.TypeClose, close.SessionId),
Build(Proto.TypeClose, close.SessionId,
close.Reason.HasValue ? [close.Reason.Value] : []),
_ => throw new InvalidOperationException($"unknown frame type: {frame.GetType()}"),
};
}
static byte[] BuildManifest(UpstreamEntry[] entries)
static byte[] BuildManifestPayload(UpstreamEntry[] entries)
{
using var ms = new MemoryStream();
ms.Write(Header(Proto.TypeManifest, 0));
foreach (var e in entries)
{
var labelBytes = Encoding.UTF8.GetBytes(e.Label ?? "");
@@ -92,26 +108,19 @@ static class FrameCodec
return ms.ToArray();
}
static byte[] Header(byte type, uint sessionId)
{
return [
Proto.Version, type,
(byte)(sessionId >> 24),
(byte)(sessionId >> 16),
(byte)(sessionId >> 8),
(byte)(sessionId & 0xFF),
];
}
public static Frame? Parse(ReadOnlySpan<byte> buf)
{
if (buf.Length < 6)
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 payload = buf[6..];
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
{