tcp: retransmit logic rollback (#61)

* tcp: remove retransmit logic entirely; add duplicate ack counting to ControlBlock * retransmit implemented in nice simple straightforward way * narrow down retransmission cases * remove old timing tests * add ControlBlock retransmit test * add failing handler test * reworking payload length semantic meaning in code * fix establish conn logic * clean up tests and add TCB dupack generation and test it * catch pending retransmit satisfy in test * add fuzz test for control block * bugfix: be more strict in what is considered dupack * add IncomingIsDupACK docs * limit queue of retransmits * protect retransmit overflow from incorrectly updating nxt
2026-09-10 08:39:30 +00:00 · 2026-03-26 11:48:02 -03:00
parent abb114fc31
commit 64b2647a5e
12 changed files with 508 additions and 889 deletions
@@ -0,0 +1,98 @@
+package tcp
+
+import (
+	"testing"
+
+	"github.com/soypat/lneto/internal"
+)
+
+func FuzzTCPControlBlock(f *testing.F) {
+	const (
+		mutopFlags = 1 << iota
+		mutopSeq
+		mutopAck
+		mutopMaxBit
+	)
+	const mutopBits = mutopMaxBit - 1
+	const (
+		mutPacketBits = 4
+
+		mutFlags = 1 << iota
+	)
+	const wnd = 1500
+	var seed uint64
+	editPkt := func(rngSeed, ops uint64, seg *Segment) {
+		ops &= mutopBits
+		if ops&mutopFlags != 0 {
+			seg.Flags ^= Flags(seed & uint64(FlagACK|FlagFIN|FlagRST|FlagSYN))
+		}
+		if ops&mutopSeq != 0 {
+			seg.SEQ = Value(int32(seg.SEQ) + int32(int8(uint8(rngSeed>>32))))
+		}
+		if ops&mutopAck != 0 {
+			seg.ACK = Value(int32(seg.ACK) + int32(int8(uint8(rngSeed>>48))))
+		}
+	}
+	f.Add(seed, uint64(mutopFlags))
+	f.Fuzz(func(t *testing.T, seed, op uint64) {
+		var tcb0, tcb1 ControlBlock
+		iss0 := Value(seed)
+		iss1 := Value(seed >> 32)
+		err := tcb0.Open(iss0, wnd)
+		if err != nil {
+			t.Fatal(err)
+		}
+		synseg := ClientSynSegment(iss1, wnd)
+		err = tcb1.Send(synseg)
+		if err != nil {
+			t.Fatal(err)
+		}
+		err = tcb0.Recv(synseg)
+		if err != nil {
+			t.Fatal(err)
+		}
+		sent := 0
+		const maxpkts = 30
+		pktEdits := internal.Prand64(seed)
+		nextOp := internal.Prand64(op)
+		for range maxpkts {
+			nextOp = internal.Prand64(nextOp)
+			seg0, ok := tcb0.PendingSegment(10)
+			if ok {
+				edit := pktEdits&1 != 0
+				pktEdits >>= 1
+				if edit {
+					editPkt(seed, nextOp, &seg0)
+				}
+				err = tcb0.Send(seg0)
+				if err == nil {
+					sent++
+					err = tcb1.Recv(seg0)
+					if err != nil {
+						t.Fatal("packet sent from TCB0 to TCB1 failed:\n", StringExchange(seg0, tcb0.State(), tcb1.State(), false))
+					}
+				}
+			}
+			nextOp = internal.Prand64(nextOp)
+			seg1, ok := tcb1.PendingSegment(10)
+			if ok {
+				edit := pktEdits&1 != 0
+				pktEdits >>= 1
+				if edit {
+					editPkt(seed, nextOp, &seg1)
+				}
+				err = tcb1.Send(seg1)
+				if err == nil {
+					sent++
+					err = tcb0.Recv(seg1)
+					if err != nil {
+						t.Fatal("packet sent from TCB1 to TCB0 failed:\n", StringExchange(seg1, tcb0.State(), tcb1.State(), true))
+					}
+				}
+			}
+		}
+		if sent == 0 {
+			t.Fatal("no packets sent")
+		}
+	})
+}