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tcp.Policy: add newTransmitLimit output

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soypat
2026-09-06 12:29:20 -07:00
parent 04f6294d9c
commit 53b606a1ff
4 changed files with 49 additions and 33 deletions
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tcp/policy_test.go
+30 -15
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@@ -21,7 +21,7 @@ type recordingPolicy struct {
keep bool // PreRx result. Default true (see newRecordingPolicy).
rtxFrom Value
retransmit bool
holdNew bool
txLimit Size // PreTx new-data limit. Default TransmitUnlimited (see newRecordingPolicy).
// writeOpts, when non-empty, is appended as TCP options by PreTx.
writeOpts []byte
}
@@ -34,7 +34,9 @@ type txRecord struct {
dport uint16
}
func newRecordingPolicy() *recordingPolicy { return &recordingPolicy{keep: true} }
func newRecordingPolicy() *recordingPolicy {
return &recordingPolicy{keep: true, txLimit: TransmitUnlimited}
}
var _ Policy = (*recordingPolicy)(nil)
@@ -49,7 +51,7 @@ func (p *recordingPolicy) PostRx(h *Handler, prevState State, accepted Frame) {
p.postRx = append(p.postRx, accepted.Segment(len(accepted.Payload())))
}
func (p *recordingPolicy) PreTx(h *Handler, outgoingOpts Frame) (Value, bool, bool) {
func (p *recordingPolicy) PreTx(h *Handler, outgoingOpts Frame) (Size, Value, bool) {
p.preTx++
if len(p.writeOpts) > 0 {
// Raise the offset first: Options() is sized from it.
@@ -57,7 +59,7 @@ func (p *recordingPolicy) PreTx(h *Handler, outgoingOpts Frame) (Value, bool, bo
outgoingOpts.SetOffsetAndFlags(words, 0)
copy(outgoingOpts.Options(), p.writeOpts)
}
return p.rtxFrom, p.retransmit, p.holdNew
return p.txLimit, p.rtxFrom, p.retransmit
}
func (p *recordingPolicy) PostTx(h *Handler, outgoing Frame) {
@@ -365,9 +367,10 @@ func TestPolicy_PreTxRetransmitOutOfRange(t *testing.T) {
}
}
// TestPolicy_HoldNew verifies holdNew suppresses new data while leaving control
// segments free to go out.
func TestPolicy_HoldNew(t *testing.T) {
// TestPolicy_TransmitLimit verifies the PreTx new-data limit caps the payload
// sent while leaving control segments free to go out: a zero limit suppresses
// data entirely, a partial limit truncates the segment.
func TestPolicy_TransmitLimit(t *testing.T) {
const mtu = ethernet.MaxMTU
rng := rand.New(rand.NewSource(10))
client, server := newHandler(t, mtu, 3), newHandler(t, mtu, 3)
@@ -378,8 +381,9 @@ func TestPolicy_HoldNew(t *testing.T) {
var buf [mtu]byte
establish(t, client, server, buf[:])
pol.holdNew = true
if _, err := client.Write([]byte("payload")); err != nil {
const payload = "payload"
pol.txLimit = 0
if _, err := client.Write([]byte(payload)); err != nil {
t.Fatal("client write:", err)
}
clear(buf[:])
@@ -388,18 +392,29 @@ func TestPolicy_HoldNew(t *testing.T) {
t.Fatal("client send:", err)
}
if n > sizeHeaderTCP {
t.Fatalf("holdNew must suppress new data, got %d payload bytes", n-sizeHeaderTCP)
t.Fatalf("a zero limit must suppress new data, got %d payload bytes", n-sizeHeaderTCP)
}
// Releasing the hold lets the same data out.
pol.holdNew = false
// A partial limit lets only that many bytes out.
pol.txLimit = 3
clear(buf[:])
n, err = client.Send(buf[:])
if err != nil {
t.Fatal("client send after hold:", err)
t.Fatal("client send under partial limit:", err)
}
if n <= sizeHeaderTCP {
t.Fatal("data must flow once holdNew is cleared")
if got := n - sizeHeaderTCP; got != int(pol.txLimit) {
t.Fatalf("got %d payload bytes, want the limit of %d", got, pol.txLimit)
}
// Releasing the limit lets the rest of the data out.
pol.txLimit = TransmitUnlimited
clear(buf[:])
n, err = client.Send(buf[:])
if err != nil {
t.Fatal("client send after limit lifted:", err)
}
if got := n - sizeHeaderTCP; got != len(payload)-3 {
t.Fatalf("got %d payload bytes, want the remaining %d once unlimited", got, len(payload)-3)
}
}