merge main fixes

x/xnet/retransmit_test.go

@@ -12,11 +12,14 @@ import (
 
 	"github.com/soypat/lneto"
 	"github.com/soypat/lneto/ethernet"
+	"github.com/soypat/lneto/tcp"
+	"github.com/soypat/lneto/tcp/rto"
 )
 
 // TestTCPRetransmitsLostSegment drops exactly one data segment and requires the
-// bytes to arrive anyway, which is what [TCPPoolConfig.NanoTime] already promises
-// in its own documentation. Without a LossRecovery installed the loss is terminal.
+// bytes to arrive anyway. It covers [TCPPoolConfig.NewPolicy] reaching the
+// pooled and dialed connections alike: without a [tcp.Policy] installed the
+// loss is terminal, which is what this test asserts against.
 func TestTCPRetransmitsLostSegment(t *testing.T) {
 	const (
 		MTU     = ethernet.MaxMTU
@@ -55,6 +58,13 @@ func TestTCPRetransmitsLostSegment(t *testing.T) {
 		EstablishedTimeout: 30 * time.Second,
 		ClosingTimeout:     30 * time.Second,
 		NewBackoff:         func() lneto.BackoffStrategy { return backoffYield },
+		NewPolicy: func() tcp.Policy {
+			timer := new(rto.Timer)
+			if err := timer.Configure(func() int64 { return time.Now().UnixNano() }); err != nil {
+				t.Fatal(err)
+			}
+			return timer
+		},
 	}
 	svGo := sv.StackBlocking(backoffYield).StackGo(StackGoConfig{ListenerPoolConfig: pool})
 	clGo := client.StackBlocking(backoffYield).StackGo(StackGoConfig{

x/xnet/stack-go.go

@@ -176,17 +176,19 @@ func (s StackGo) SocketNetip(ctx context.Context, network string, family, sotype
 		if isDial {
 			var conn tcp.Conn
 			// DIAL TCP: active connection a.k.a TCP Client branch.
-			err = conn.Configure(tcp.ConnConfig{
+			conncfg := tcp.ConnConfig{
 				// TODO(pato): Eventually add UDP configuration. we use TCP for now for simplicity's sake.
 				TxBuf:             make([]byte, s.plcfg.TxBufSize),
 				RxBuf:             make([]byte, s.plcfg.RxBufSize),
 				TxPacketQueueSize: s.plcfg.QueueSize,
 				RWBackoff:         s.plcfg.NewBackoff(),
-				// A dialed connection needs a retransmission timer as much as a
-				// pooled one. See [NewTCPPool].
-				LossRecovery: new(tcp.RTO),
-				Nanotime:     s.blk.nanotime,
-			})
+			}
+			if s.plcfg.NewPolicy != nil {
+				// A dialed connection needs loss recovery as much as a pooled
+				// one. See [TCPPoolConfig.NewPolicy].
+				conncfg.Policy = s.plcfg.NewPolicy()
+			}
+			err = conn.Configure(conncfg)
 			if err != nil {
 				return nil, err
 			}

x/xnet/tcppool.go

@@ -42,8 +42,9 @@ type TCPPoolConfig struct {
 	ConnLogger *slog.Logger
 
 	// NanoTime returns the current monotonic time in nanoseconds.
-	// Used for pool timeout tracking and passed to each [tcp.Conn] for
-	// retransmission timing (RFC 6298). If nil, defaults to time.Now().UnixNano().
+	// Used for pool timeout tracking. If nil, defaults to time.Now().UnixNano().
+	// Retransmission timing is not driven by this clock: a [tcp.Policy] carries
+	// its own. See NewPolicy.
 	NanoTime func() int64
 	// EstablishedTimeout sets the timeout for a TCP connection since it is acquired until it is established.
 	// If the connection does not establish in this time it will be closed by the pool.
@@ -56,6 +57,9 @@ type TCPPoolConfig struct {
 	// NewBackoff returns the backoff to use for every newly configured TCP connection. Must be non-nil.
 	// This should always return a static(non-method) function unless you know what you are doing.
 	NewBackoff func() lneto.BackoffStrategy
+	// NewPolicy if non-nil creates a [tcp.Policy] for each [tcp.Conn] used by the configured Listener.
+	// NewPolicy should not return reused policies unless the algorithm is stateless. See [tcp.Policy] for more information.
+	NewPolicy func() tcp.Policy
 }
 
 func NewTCPPool(cfg TCPPoolConfig) (*TCPPool, error) {
@@ -87,11 +91,11 @@ func NewTCPPool(cfg TCPPoolConfig) (*TCPPool, error) {
 			TxPacketQueueSize: cfg.QueueSize,
 			Logger:            cfg.ConnLogger,
 			RWBackoff:         cfg.NewBackoff(),
-			// Retransmission timing, as NanoTime's contract promises. One RTO per
-			// connection: it shadows that connection's send sequence space and so
-			// cannot be shared.
-			LossRecovery: new(tcp.RTO),
-			Nanotime:     pool.now,
+		}
+		if cfg.NewPolicy != nil {
+			// One Policy per connection: it shadows that connection's send
+			// sequence space and so cannot be shared.
+			conncfg.Policy = cfg.NewPolicy()
 		}
 		err := pool.conns[i].Configure(conncfg)
 		if err != nil {