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tcp: bugfix for seq not in snd/rcv.wnd error (#49)

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* tcp: bugfix for seq not in snd/rcv.wnd error

* accept dupe ACKs for window updates and prevent decrement of UNA

* add fixes for incorrect tcp functioning

* remove Conn.Available* methods in favor of Conn.Free* methods due to ambiguous name
This commit is contained in:
Pat Whittingslow
2026-03-04 16:59:30 +01:00
committed by GitHub
parent 02b4e71c2a
commit d5c4fa53c6
10 changed files with 600 additions and 85 deletions
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tcp/tcp_legacy_test.go
+17 -11
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@@ -285,24 +285,26 @@ a FIN from A, acknowledges it, then later closes and sends its own FIN.
*/
func TestExchange_rfc9293_figure12_peerB(t *testing.T) {
const issA, issB, windowA, windowB = 100, 300, 1000, 1000
// Note: After B sends an ACK in CLOSE-WAIT, the implementation auto-queues FIN|ACK.
// This is an optimization that combines steps 3 and 4 of RFC 9293 Figure 12.
exchangeB := []tcp.Exchange{
0: { // B receives FIN|ACK from A, goes to CLOSE-WAIT with pending ACK.
// RFC 9293 Figure 12 steps 2-3: B receives FIN|ACK, then sends back ACK.
// B remains in CLOSE-WAIT, able to keep sending (RFC 9293 §3.5).
exchangeBeforeClose := []tcp.Exchange{
0: { // Step 2: B receives FIN|ACK from A, goes to CLOSE-WAIT with pending ACK.
Incoming: &tcp.Segment{SEQ: issA, ACK: issB, Flags: FINACK, WND: windowA},
WantState: tcp.StateCloseWait,
WantPending: &tcp.Segment{SEQ: issB, ACK: issA + 1, Flags: tcp.FlagACK, WND: windowB},
},
1: { // B sends ACK to A. Implementation auto-queues FIN|ACK for close.
Outgoing: &tcp.Segment{SEQ: issB, ACK: issA + 1, Flags: tcp.FlagACK, WND: windowB},
WantState: tcp.StateCloseWait,
WantPending: &tcp.Segment{SEQ: issB, ACK: issA + 1, Flags: FINACK, WND: windowB},
1: { // Step 3: B sends ACK to A. B remains in CLOSE-WAIT.
Outgoing: &tcp.Segment{SEQ: issB, ACK: issA + 1, Flags: tcp.FlagACK, WND: windowB},
WantState: tcp.StateCloseWait,
},
2: { // B sends FIN|ACK to A, goes to LAST-ACK.
}
// RFC 9293 Figure 12 step 4: B calls Close(). Queues FIN|ACK, goes to LAST-ACK.
exchangeAfterClose := []tcp.Exchange{
0: { // Step 4: B sends FIN|ACK to A, goes to LAST-ACK.
Outgoing: &tcp.Segment{SEQ: issB, ACK: issA + 1, Flags: FINACK, WND: windowB},
WantState: tcp.StateLastAck,
},
3: { // B receives final ACK from A, goes to CLOSED.
1: { // Step 5: B receives final ACK from A, goes to CLOSED.
Incoming: &tcp.Segment{SEQ: issA + 1, ACK: issB + 1, Flags: tcp.FlagACK, WND: windowA},
WantState: tcp.StateClosed,
},
@@ -310,7 +312,11 @@ func TestExchange_rfc9293_figure12_peerB(t *testing.T) {
var tcbB tcp.ControlBlock
tcbB.HelperInitState(tcp.StateEstablished, issB, issB, windowB)
tcbB.HelperInitRcv(issA, issA, windowA)
tcbB.HelperExchange(t, exchangeB)
tcbB.HelperExchange(t, exchangeBeforeClose)
if err := tcbB.Close(); err != nil { // Step 4: (Close) from RFC Figure 12.
t.Fatal("close:", err)
}
tcbB.HelperExchange(t, exchangeAfterClose)
}
/*