Represent direction with boolean

...since direction can only hold one of two possible values.

PiperOrigin-RevId: 402855698

pkg/tcpip/stack/conntrack.go

@@ -37,14 +37,6 @@ import (
 // Our hash table has 16K buckets.
 const numBuckets = 1 << 14
 
-// Direction of the tuple.
-type direction int
-
-const (
-	dirOriginal direction = iota
-	dirReply
-)
-
 // tuple holds a connection's identifying and manipulating data in one
 // direction. It is immutable.
 //
@@ -56,8 +48,9 @@ type tuple struct {
 	// conn is the connection tracking entry this tuple belongs to.
 	conn *conn
 
-	// direction is the direction of the tuple.
-	direction direction
+	// reply is true iff the tuple's direction is opposite that of the first
+	// packet seen on the connection.
+	reply bool
 
 	mu sync.RWMutex `state:"nosave"`
 	// +checklocks:mu
@@ -155,7 +148,7 @@ func (cn *conn) timedOut(now time.Time) bool {
 //
 // TODO(https://gvisor.dev/issue/6590): annotate r/w locking requirements.
 // +checklocks:cn.mu
-func (cn *conn) updateLocked(pkt *PacketBuffer, dir direction) {
+func (cn *conn) updateLocked(pkt *PacketBuffer, reply bool) {
 	if pkt.TransportProtocolNumber != header.TCPProtocolNumber {
 		return
 	}
@@ -170,13 +163,10 @@ func (cn *conn) updateLocked(pkt *PacketBuffer, dir direction) {
 		return
 	}
 
-	switch dir {
-	case dirOriginal:
-		cn.tcb.UpdateStateOutbound(tcpHeader)
-	case dirReply:
+	if reply {
 		cn.tcb.UpdateStateInbound(tcpHeader)
-	default:
-		panic(fmt.Sprintf("unhandled dir = %d", dir))
+	} else {
+		cn.tcb.UpdateStateOutbound(tcpHeader)
 	}
 }
 
@@ -277,8 +267,8 @@ func (ct *ConnTrack) getConnOrMaybeInsertNoop(pkt *PacketBuffer) *tuple {
 	// for this new connection.
 	conn := &conn{
 		ct:       ct,
-		original: tuple{tupleID: tid, direction: dirOriginal},
-		reply:    tuple{tupleID: tid.reply(), direction: dirReply},
+		original: tuple{tupleID: tid},
+		reply:    tuple{tupleID: tid.reply(), reply: true},
 		lastUsed: now,
 	}
 	conn.original.conn = conn
@@ -458,24 +448,13 @@ func (cn *conn) handlePacket(pkt *PacketBuffer, hook Hook, r *Route) bool {
 	// validated if checksum offloading is off. It may require IP defrag if the
 	// packets are fragmented.
 
-	dir := pkt.tuple.direction
+	reply := pkt.tuple.reply
 	tid, performManip := func() (tupleID, bool) {
 		cn.mu.Lock()
 		defer cn.mu.Unlock()
 
 		var tuple *tuple
-		switch dir {
-		case dirOriginal:
-			if dnat {
-				if !cn.destinationManip {
-					return tupleID{}, false
-				}
-			} else if !cn.sourceManip {
-				return tupleID{}, false
-			}
-
-			tuple = &cn.reply
-		case dirReply:
+		if reply {
 			if dnat {
 				if !cn.sourceManip {
 					return tupleID{}, false
@@ -485,14 +464,22 @@ func (cn *conn) handlePacket(pkt *PacketBuffer, hook Hook, r *Route) bool {
 			}
 
 			tuple = &cn.original
-		default:
-			panic(fmt.Sprintf("unhandled dir = %d", dir))
+		} else {
+			if dnat {
+				if !cn.destinationManip {
+					return tupleID{}, false
+				}
+			} else if !cn.sourceManip {
+				return tupleID{}, false
+			}
+
+			tuple = &cn.reply
 		}
 
 		// Mark the connection as having been used recently so it isn't reaped.
 		cn.lastUsed = time.Now()
 		// Update connection state.
-		cn.updateLocked(pkt, dir)
+		cn.updateLocked(pkt, reply)
 
 		return tuple.id(), true
 	}()
@@ -637,10 +624,10 @@ func (ct *ConnTrack) reapTupleLocked(tuple *tuple, bktID int, bkt *bucket, now t
 // TODO(https://gvisor.dev/issue/6590): annotate r/w locking requirements.
 // +checklocks:b.mu
 func removeConnFromBucket(b *bucket, tuple *tuple) {
-	if tuple.direction == dirOriginal {
-		b.tuples.Remove(&tuple.conn.reply)
-	} else {
+	if tuple.reply {
 		b.tuples.Remove(&tuple.conn.original)
+	} else {
+		b.tuples.Remove(&tuple.conn.reply)
 	}
 }