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tcp: mss honoring; accept syn with ECE/CWR flags; add RSTQueue type (#41)

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* tcp: mss honoring; accept syn with ECE/CWR flags; add RSTQueue type

* tcp: move option logic to own file

* remove prints in pcap

* add MSS send threshold inspired by linux/freebsd/lwip thresh
This commit is contained in:
Pat Whittingslow
2026-02-25 16:58:55 +01:00
committed by GitHub
parent 58a9bf57e5
commit be949d960c
10 changed files with 570 additions and 191 deletions
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internet/stack-ports.go
+22 -1
View File
@@ -11,6 +11,7 @@ import (
"github.com/soypat/lneto"
"github.com/soypat/lneto/ethernet"
"github.com/soypat/lneto/internal"
"github.com/soypat/lneto/tcp"
)
type StackPorts struct {
@@ -18,7 +19,8 @@ type StackPorts struct {
handlers handlers
dstPortOff uint16
protocol uint16
// stores last node to demux/encapsulate.
// rstQueue stores pending RST responses for TCP SYNs to unregistered ports.
rstQueue tcp.RSTQueue
}
func (ps *StackPorts) ResetUDP(maxNodes int) error {
@@ -56,6 +58,9 @@ func (ps *StackPorts) Encapsulate(carrierData []byte, offsetToIP, offsetToFrame
return 0, io.ErrShortBuffer
}
_, n, err = ps.handlers.encapsulateAny(carrierData, offsetToIP, offsetToFrame)
if n == 0 {
n, _ = ps.rstQueue.Drain(carrierData, offsetToIP, offsetToFrame)
}
return n, err
}
@@ -65,6 +70,19 @@ func (ps *StackPorts) Demux(b []byte, offset int) (err error) {
}
port := binary.BigEndian.Uint16(b[int(ps.dstPortOff)+offset:])
_, err = ps.handlers.demuxByPort(b, offset, port)
if err == lneto.ErrPacketDrop && ps.protocol == uint16(lneto.IPProtoTCP) && offset+14 <= len(b) {
// RFC 9293 §3.10.7.1: RST for SYN to port with no listener.
flags := binary.BigEndian.Uint16(b[offset+12:]) & 0x01ff
const flagSYN, flagRST, flagACK = 0x02, 0x04, 0x10
if flags&flagSYN != 0 && flags&(flagRST|flagACK) == 0 {
srcaddr, _, _, _, iperr := internal.GetIPAddr(b)
if iperr == nil {
remotePort := binary.BigEndian.Uint16(b[offset:])
segSeq := tcp.Value(binary.BigEndian.Uint32(b[offset+4:]))
ps.rstQueue.Queue(srcaddr, remotePort, port, 0, segSeq+1, tcp.FlagRST|tcp.FlagACK)
}
}
}
return err
}
@@ -149,5 +167,8 @@ func (ps *StackPortsMACFiltered) Encapsulate(carrierData []byte, offsetToIP, off
h.error("handlers:encapsulate", slog.String("func", "encapsulateAny"), slog.String("ctx", h.context), slog.String("err", err.Error()))
}
}
if n, _ := ps.sp.rstQueue.Drain(carrierData, offsetToIP, offsetToFrame); n > 0 {
return n, nil
}
return 0, err // Return last written error.
}