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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/handler_test.go
+10 -10
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@@ -266,7 +266,7 @@ func TestTxBufferFreedOnACK(t *testing.T) {
establish(t, client, server, rawbuf[:])
// Record initial available space.
initialAvailable := client.AvailableOutput()
initialAvailable := client.FreeOutput()
if initialAvailable == 0 {
t.Fatal("expected non-zero initial available output")
}
@@ -284,7 +284,7 @@ func TestTxBufferFreedOnACK(t *testing.T) {
}
// Available space should have decreased.
afterWriteAvailable := client.AvailableOutput()
afterWriteAvailable := client.FreeOutput()
if afterWriteAvailable >= initialAvailable {
t.Fatalf("expected available to decrease after write: before=%d, after=%d",
initialAvailable, afterWriteAvailable)
@@ -303,7 +303,7 @@ func TestTxBufferFreedOnACK(t *testing.T) {
// After sending, data moves from "unsent" to "sent" - available should still be reduced
// until we receive an ACK.
afterSendAvailable := client.AvailableOutput()
afterSendAvailable := client.FreeOutput()
// Server receives DATA.
err = server.Recv(dataPacket)
@@ -329,7 +329,7 @@ func TestTxBufferFreedOnACK(t *testing.T) {
// THE BUG: After receiving ACK, the TX buffer should be freed.
// Without the fix, AvailableOutput() stays at the post-send value.
afterAckAvailable := client.AvailableOutput()
afterAckAvailable := client.FreeOutput()
if afterAckAvailable <= afterSendAvailable {
t.Fatalf("BUG (issue #22): TX buffer not freed after receiving ACK\n"+
@@ -384,7 +384,7 @@ func TestWindowUpdateAfterRead(t *testing.T) {
establish(t, client, server, rawbuf[:])
// Fill the server's RX buffer completely (without reading).
fillData := make([]byte, server.FreeRx())
fillData := make([]byte, server.FreeInput())
n, err := client.Write(fillData)
if err != nil {
t.Fatal("client write:", err)
@@ -400,8 +400,8 @@ func TestWindowUpdateAfterRead(t *testing.T) {
if err != nil {
t.Fatal("server recv:", err)
}
if server.FreeRx() != 0 {
t.Fatalf("expected server RX buffer full, got %d free", server.FreeRx())
if server.FreeInput() != 0 {
t.Fatalf("expected server RX buffer full, got %d free", server.FreeInput())
}
// Server sends ACK — should advertise Window=0.
@@ -451,7 +451,7 @@ func TestWindowUpdateAfterRead(t *testing.T) {
if wnd := wndFrm.WindowSize(); wnd == 0 {
t.Fatal("BUG: window update ACK still has Window=0")
}
t.Logf("window update sent: Window=%d (buffer free=%d)", wndFrm.WindowSize(), server.FreeRx())
t.Logf("window update sent: Window=%d (buffer free=%d)", wndFrm.WindowSize(), server.FreeInput())
}
// TestWindowUpdateSWSAvoidance verifies that small reads that free less than
@@ -486,7 +486,7 @@ func TestWindowUpdateSWSAvoidance(t *testing.T) {
establish(t, client, server, rawbuf[:])
// Fill most of the server's RX buffer (leave a tiny amount free).
fillSize := server.FreeRx() - 10
fillSize := server.FreeInput() - 10
fillData := make([]byte, fillSize)
for i := range fillData {
fillData[i] = byte(i)
@@ -542,7 +542,7 @@ func TestWindowUpdateSWSAvoidance(t *testing.T) {
t.Logf("NOTE: window update sent after small read (freed %d of %d buffer)", len(smallRead), rxBufSize)
// This is acceptable if the threshold is met, but for SWS avoidance
// we expect no update when the freed increment is < bufSize/2.
freeAfterRead := Size(server.FreeRx())
freeAfterRead := Size(server.FreeInput())
if freeAfterRead < Size(rxBufSize/2) {
t.Fatalf("SWS violation: window update sent when free=%d < bufSize/2=%d", freeAfterRead, rxBufSize/2)
}