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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_test.go
+17 -13
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@@ -34,16 +34,15 @@ func TestExchangeTest_PassiveClose_FINACKRegression(t *testing.T) {
BState: tcp.StateCloseWait,
BPending: &tcp.Segment{SEQ: issB, ACK: issA + 1, Flags: tcp.FlagACK, WND: windowB},
},
1: { // B sends ACK to A. Auto-queues FIN|ACK in CLOSE-WAIT.
Seg: tcp.Segment{SEQ: issB, ACK: issA + 1, Flags: tcp.FlagACK, WND: windowB},
Action: tcp.StepBSends,
AState: tcp.StateFinWait2,
BState: tcp.StateCloseWait,
BPending: &tcp.Segment{SEQ: issB, ACK: issA + 1, Flags: FINACK, WND: windowB},
1: { // B sends ACK to A (RFC 9293 Figure 12 step 3). B stays in CLOSE-WAIT.
Seg: tcp.Segment{SEQ: issB, ACK: issA + 1, Flags: tcp.FlagACK, WND: windowB},
Action: tcp.StepBSends,
AState: tcp.StateFinWait2,
BState: tcp.StateCloseWait,
},
2: { // B calls Close(). Goes to LAST-ACK. Pending must be FIN|ACK combined.
// This is the regression check: Close() must NOT overwrite the auto-queued
// FIN|ACK with [FlagFIN, FlagACK] in separate pending slots.
2: { // B calls Close() (RFC 9293 Figure 12 step 4). Goes to LAST-ACK.
// Regression check: Close() must queue FIN|ACK as a single combined flag
// in pending[0], not as [FlagFIN, FlagACK] in separate pending slots.
Action: tcp.StepBCloses,
AState: tcp.StateFinWait2, // A unchanged.
BState: tcp.StateLastAck,
@@ -79,7 +78,7 @@ func TestExchangeTest_figure12(t *testing.T) {
InitStateA: tcp.StateEstablished,
InitStateB: tcp.StateEstablished,
Steps: []tcp.SegmentStep{
0: { // A sends FIN|ACK to B.
0: { // A sends FIN|ACK to B (RFC 9293 Figure 12 step 2).
Seg: tcp.Segment{SEQ: issA, ACK: issB, Flags: FINACK, WND: windowA},
Action: tcp.StepASends,
AState: tcp.StateFinWait1,
@@ -87,15 +86,20 @@ func TestExchangeTest_figure12(t *testing.T) {
APending: nil,
BPending: &tcp.Segment{SEQ: issB, ACK: issA + 1, Flags: tcp.FlagACK, WND: windowB},
},
1: { // B sends ACK to A. (Auto-queues FIN|ACK in CLOSE-WAIT)
1: { // B sends ACK to A (RFC 9293 Figure 12 step 3). B stays in CLOSE-WAIT.
Seg: tcp.Segment{SEQ: issB, ACK: issA + 1, Flags: tcp.FlagACK, WND: windowB},
Action: tcp.StepBSends,
AState: tcp.StateFinWait2,
BState: tcp.StateCloseWait,
APending: &tcp.Segment{SEQ: issA + 1, ACK: issB, Flags: tcp.FlagACK, WND: windowA}, // TODO: should be nil?
},
2: { // B calls Close() (RFC 9293 Figure 12 step 4). B goes to LAST-ACK.
Action: tcp.StepBCloses,
AState: tcp.StateFinWait2,
BState: tcp.StateLastAck,
BPending: &tcp.Segment{SEQ: issB, ACK: issA + 1, Flags: FINACK, WND: windowB},
},
2: { // B sends FIN|ACK to A.
3: { // B sends FIN|ACK to A (RFC 9293 Figure 12 step 4 cont).
Seg: tcp.Segment{SEQ: issB, ACK: issA + 1, Flags: FINACK, WND: windowB},
Action: tcp.StepBSends,
AState: tcp.StateTimeWait,
@@ -103,7 +107,7 @@ func TestExchangeTest_figure12(t *testing.T) {
APending: &tcp.Segment{SEQ: issA + 1, ACK: issB + 1, Flags: tcp.FlagACK, WND: windowA},
BPending: nil,
},
3: { // A sends final ACK to B.
4: { // A sends final ACK to B (RFC 9293 Figure 12 step 5).
Seg: tcp.Segment{SEQ: issA + 1, ACK: issB + 1, Flags: tcp.FlagACK, WND: windowA},
Action: tcp.StepASends,
AState: tcp.StateTimeWait,