xnet: Tracer -> TraceReceiver

Rename the interface that specifies methods to be implemented by trace
receivers. Reason is that in the next patch we'll need to expose
"Tracer" as the tracing networker itself.

xnet/trace.go

-// Copyright (C) 2017-2020  Nexedi SA and Contributors.
+// Copyright (C) 2017-2021  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -41,12 +41,12 @@ import (
 //    - for similar reasons.
 //
 // WARNING NetTrace functionality is currently very draft.
-func NetTrace(inner Networker, tracer Tracer) Networker {
-	return &netTrace{inner, tracer}
+func NetTrace(inner Networker, tracerx TraceReceiver) Networker {
+	return &netTrace{inner, tracerx}
 }
 
-// Tracer is the interface that needs to be implemented by network trace receivers.
-type Tracer interface {
+// TraceReceiver is the interface that needs to be implemented by network trace receivers.
+type TraceReceiver interface {
 	TraceNetDial(*TraceDial)
 	TraceNetConnect(*TraceConnect)
 	TraceNetListen(*TraceListen)
@@ -83,8 +83,8 @@ type TraceTx struct {
 // netTrace wraps underlying Networker such that whenever a connection is created
 // it is wrapped with traceConn.
 type netTrace struct {
-	inner  Networker
-	tracer Tracer
+	inner Networker
+	rx    TraceReceiver
 }
 
 func (nt *netTrace) Network() string {
@@ -101,12 +101,12 @@ func (nt *netTrace) Close() error {
 }
 
 func (nt *netTrace) Dial(ctx context.Context, addr string) (net.Conn, error) {
-	nt.tracer.TraceNetDial(&TraceDial{Dialer: nt.inner.Name(), Addr: addr})
+	nt.rx.TraceNetDial(&TraceDial{Dialer: nt.inner.Name(), Addr: addr})
 	c, err := nt.inner.Dial(ctx, addr)
 	if err != nil {
 		return nil, err
 	}
-	nt.tracer.TraceNetConnect(&TraceConnect{Src: c.LocalAddr(), Dst: c.RemoteAddr(), Dialed: addr})
+	nt.rx.TraceNetConnect(&TraceConnect{Src: c.LocalAddr(), Dst: c.RemoteAddr(), Dialed: addr})
 	return &traceConn{nt, c}, nil
 }
 
@@ -116,7 +116,7 @@ func (nt *netTrace) Listen(ctx context.Context, laddr string) (Listener, error)
 	if err != nil {
 		return nil, err
 	}
-	nt.tracer.TraceNetListen(&TraceListen{Laddr: l.Addr()})
+	nt.rx.TraceNetListen(&TraceListen{Laddr: l.Addr()})
 	return &netTraceListener{nt, l}, nil
 }
 
@@ -144,7 +144,7 @@ func (tc *traceConn) Write(b []byte) (int, error) {
 	// XXX +TraceNetTxPre ?
 	n, err := tc.Conn.Write(b)
 	if err == nil {
-		tc.nt.tracer.TraceNetTx(&TraceTx{Src: tc.LocalAddr(), Dst: tc.RemoteAddr(), Pkt: b})
+		tc.nt.rx.TraceNetTx(&TraceTx{Src: tc.LocalAddr(), Dst: tc.RemoteAddr(), Pkt: b})
 	}
 	return n, err
 }