Simplify redundant LocalTrafficDetector implementations

All of the LocalTrafficDetector implementations were essentially
identical after construction time, so just reduce them to a single
implementation with multiple constructors.

Also, improve the comments.

pkg/proxy/util/localdetector.go

@@ -22,61 +22,62 @@ import (
 	netutils "k8s.io/utils/net"
 )
 
-// LocalTrafficDetector in a interface to take action (jump) based on whether traffic originated locally
-// at the node or not
+// LocalTrafficDetector generates iptables or nftables rules to detect traffic from local pods.
 type LocalTrafficDetector interface {
-	// IsImplemented returns true if the implementation does something, false otherwise
+	// IsImplemented returns true if the implementation does something, false
+	// otherwise. You should not call the other methods if IsImplemented() returns
+	// false.
 	IsImplemented() bool
 
-	// IfLocal returns iptables arguments that will match traffic from a pod
+	// IfLocal returns iptables arguments that will match traffic from a local pod.
 	IfLocal() []string
 
-	// IfNotLocal returns iptables arguments that will match traffic that is not from a pod
+	// IfNotLocal returns iptables arguments that will match traffic that is not from
+	// a local pod.
 	IfNotLocal() []string
 
-	// IfLocalNFT returns nftables arguments that will match traffic from a pod
+	// IfLocalNFT returns nftables arguments that will match traffic from a local pod.
 	IfLocalNFT() []string
 
-	// IfNotLocalNFT returns nftables arguments that will match traffic that is not from a pod
+	// IfNotLocalNFT returns nftables arguments that will match traffic that is not
+	// from a local pod.
 	IfNotLocalNFT() []string
 }
 
-type noOpLocalDetector struct{}
-
-// NewNoOpLocalDetector is a no-op implementation of LocalTrafficDetector
-func NewNoOpLocalDetector() LocalTrafficDetector {
-	return &noOpLocalDetector{}
-}
-
-func (n *noOpLocalDetector) IsImplemented() bool {
-	return false
-}
-
-func (n *noOpLocalDetector) IfLocal() []string {
-	return nil // no-op; matches all traffic
-}
-
-func (n *noOpLocalDetector) IfNotLocal() []string {
-	return nil // no-op; matches all traffic
-}
-
-func (n *noOpLocalDetector) IfLocalNFT() []string {
-	return nil // no-op; matches all traffic
-}
-
-func (n *noOpLocalDetector) IfNotLocalNFT() []string {
-	return nil // no-op; matches all traffic
-}
-
-type detectLocalByCIDR struct {
+type detectLocal struct {
 	ifLocal       []string
 	ifNotLocal    []string
 	ifLocalNFT    []string
 	ifNotLocalNFT []string
 }
 
-// NewDetectLocalByCIDR implements the LocalTrafficDetector interface using a CIDR. This can be used when a single CIDR
-// range can be used to capture the notion of local traffic.
+func (d *detectLocal) IsImplemented() bool {
+	return len(d.ifLocal) > 0
+}
+
+func (d *detectLocal) IfLocal() []string {
+	return d.ifLocal
+}
+
+func (d *detectLocal) IfNotLocal() []string {
+	return d.ifNotLocal
+}
+
+func (d *detectLocal) IfLocalNFT() []string {
+	return d.ifLocalNFT
+}
+
+func (d *detectLocal) IfNotLocalNFT() []string {
+	return d.ifNotLocalNFT
+}
+
+// NewNoOpLocalDetector returns a no-op implementation of LocalTrafficDetector.
+func NewNoOpLocalDetector() LocalTrafficDetector {
+	return &detectLocal{}
+}
+
+// NewDetectLocalByCIDR returns a LocalTrafficDetector that considers traffic from the
+// provided cidr to be from a local pod, and other traffic to be non-local.
 func NewDetectLocalByCIDR(cidr string) (LocalTrafficDetector, error) {
 	_, parsed, err := netutils.ParseCIDRSloppy(cidr)
 	if err != nil {
@@ -88,7 +89,7 @@ func NewDetectLocalByCIDR(cidr string) (LocalTrafficDetector, error) {
 		nftFamily = "ip6"
 	}
 
-	return &detectLocalByCIDR{
+	return &detectLocal{
 		ifLocal:       []string{"-s", cidr},
 		ifNotLocal:    []string{"!", "-s", cidr},
 		ifLocalNFT:    []string{nftFamily, "saddr", cidr},
@@ -96,40 +97,14 @@ func NewDetectLocalByCIDR(cidr string) (LocalTrafficDetector, error) {
 	}, nil
 }
 
-func (d *detectLocalByCIDR) IsImplemented() bool {
-	return true
-}
-
-func (d *detectLocalByCIDR) IfLocal() []string {
-	return d.ifLocal
-}
-
-func (d *detectLocalByCIDR) IfNotLocal() []string {
-	return d.ifNotLocal
-}
-
-func (d *detectLocalByCIDR) IfLocalNFT() []string {
-	return d.ifLocalNFT
-}
-
-func (d *detectLocalByCIDR) IfNotLocalNFT() []string {
-	return d.ifNotLocalNFT
-}
-
-type detectLocalByBridgeInterface struct {
-	ifLocal       []string
-	ifNotLocal    []string
-	ifLocalNFT    []string
-	ifNotLocalNFT []string
-}
-
-// NewDetectLocalByBridgeInterface implements the LocalTrafficDetector interface using a bridge interface name.
-// This can be used when a bridge can be used to capture the notion of local traffic from pods.
+// NewDetectLocalByBridgeInterface returns a LocalTrafficDetector that considers traffic
+// from interfaceName to be from a local pod, and traffic from other interfaces to be
+// non-local.
 func NewDetectLocalByBridgeInterface(interfaceName string) (LocalTrafficDetector, error) {
 	if len(interfaceName) == 0 {
 		return nil, fmt.Errorf("no bridge interface name set")
 	}
-	return &detectLocalByBridgeInterface{
+	return &detectLocal{
 		ifLocal:       []string{"-i", interfaceName},
 		ifNotLocal:    []string{"!", "-i", interfaceName},
 		ifLocalNFT:    []string{"iif", interfaceName},
@@ -137,64 +112,17 @@ func NewDetectLocalByBridgeInterface(interfaceName string) (LocalTrafficDetector
 	}, nil
 }
 
-func (d *detectLocalByBridgeInterface) IsImplemented() bool {
-	return true
-}
-
-func (d *detectLocalByBridgeInterface) IfLocal() []string {
-	return d.ifLocal
-}
-
-func (d *detectLocalByBridgeInterface) IfNotLocal() []string {
-	return d.ifNotLocal
-}
-
-func (d *detectLocalByBridgeInterface) IfLocalNFT() []string {
-	return d.ifLocalNFT
-}
-
-func (d *detectLocalByBridgeInterface) IfNotLocalNFT() []string {
-	return d.ifNotLocalNFT
-}
-
-type detectLocalByInterfaceNamePrefix struct {
-	ifLocal       []string
-	ifNotLocal    []string
-	ifLocalNFT    []string
-	ifNotLocalNFT []string
-}
-
-// NewDetectLocalByInterfaceNamePrefix implements the LocalTrafficDetector interface using an interface name prefix.
-// This can be used when a pod interface name prefix can be used to capture the notion of local traffic. Note
-// that this will match on all interfaces that start with the given prefix.
+// NewDetectLocalByInterfaceNamePrefix returns a LocalTrafficDetector that considers
+// traffic from interfaces starting with interfacePrefix to be from a local pod, and
+// traffic from other interfaces to be non-local.
 func NewDetectLocalByInterfaceNamePrefix(interfacePrefix string) (LocalTrafficDetector, error) {
 	if len(interfacePrefix) == 0 {
 		return nil, fmt.Errorf("no interface prefix set")
 	}
-	return &detectLocalByInterfaceNamePrefix{
+	return &detectLocal{
 		ifLocal:       []string{"-i", interfacePrefix + "+"},
 		ifNotLocal:    []string{"!", "-i", interfacePrefix + "+"},
 		ifLocalNFT:    []string{"iif", interfacePrefix + "*"},
 		ifNotLocalNFT: []string{"iif", "!=", interfacePrefix + "*"},
 	}, nil
 }
-
-func (d *detectLocalByInterfaceNamePrefix) IsImplemented() bool {
-	return true
-}
-
-func (d *detectLocalByInterfaceNamePrefix) IfLocal() []string {
-	return d.ifLocal
-}
-
-func (d *detectLocalByInterfaceNamePrefix) IfNotLocal() []string {
-	return d.ifNotLocal
-}
-
-func (d *detectLocalByInterfaceNamePrefix) IfLocalNFT() []string {
-	return d.ifLocalNFT
-}
-
-func (d *detectLocalByInterfaceNamePrefix) IfNotLocalNFT() []string {
-	return d.ifNotLocalNFT
-}