Add test for redirect port

Fix the indentation and print statements.
Moved the NAT redirect tests to new file.
Added negative test to check redirect rule on ports other than
redirected port.

test/iptables/BUILD

@@ -8,6 +8,7 @@ go_library(
         "filter_input.go",
         "iptables.go",
         "iptables_util.go",
+        "nat.go",
     ],
     importpath = "gvisor.dev/gvisor/test/iptables",
     visibility = ["//test/iptables:__subpackages__"],

test/iptables/filter_input.go

@@ -23,7 +23,6 @@ import (
 const (
 	dropPort         = 2401
 	acceptPort       = 2402
-	redirectPort     = 42
 	sendloopDuration = 2 * time.Second
 	network          = "udp4"
 )
@@ -32,7 +31,6 @@ func init() {
 	RegisterTestCase(FilterInputDropUDP{})
 	RegisterTestCase(FilterInputDropUDPPort{})
 	RegisterTestCase(FilterInputDropDifferentUDPPort{})
-	RegisterTestCase(FilterInputRedirectUDPPort{})
 }
 
 // FilterInputDropUDP tests that we can drop UDP traffic.
@@ -124,29 +122,3 @@ func (FilterInputDropDifferentUDPPort) ContainerAction(ip net.IP) error {
 func (FilterInputDropDifferentUDPPort) LocalAction(ip net.IP) error {
 	return sendUDPLoop(ip, acceptPort, sendloopDuration)
 }
-
-// FilterInputRedirectUDPPort tests that packets are redirected to different port.
-type FilterInputRedirectUDPPort struct{}
-
-// Name implements TestCase.Name.
-func (FilterInputRedirectUDPPort) Name() string {
-        return "FilterInputRedirectUDPPort"
-}
-
-// ContainerAction implements TestCase.ContainerAction.
-func (FilterInputRedirectUDPPort) ContainerAction(ip net.IP) error {
-        if err := filterTable("-t", "nat", "-A", "PREROUTING", "-p", "udp", "-j", "REDIRECT", "--to-ports", fmt.Sprintf("%d", redirectPort)); err != nil {
-		return err
-	}
-
-	if err := listenUDP(redirectPort, sendloopDuration); err != nil {
-	        return fmt.Errorf("packets on port %d should be allowed, but encountered an error: %v", acceptPort, redirectPort, err)
-	}
-
-	return nil
-}
-
-// LocalAction implements TestCase.LocalAction.
-func (FilterInputRedirectUDPPort) LocalAction(ip net.IP) error {
-        return sendUDPLoop(ip, acceptPort, sendloopDuration)
-}

test/iptables/iptables_test.go

@@ -178,9 +178,14 @@ func TestFilterInputDropDifferentUDPPort(t *testing.T) {
 	}
 }
 
-func TestFilterInputRedirectUDPPort(t *testing.T) {
-	if err := singleTest(FilterInputRedirectUDPPort{}); err != nil {
+func TestFilterNATRedirectUDPPort(t *testing.T) {
+	if err := singleTest(FilterNATRedirectUDPPort{}); err != nil {
 		t.Fatal(err)
 	}
 }
 
+func TestFilterNATDropUDP(t *testing.T) {
+        if err := singleTest(FilterNATDropUDP{}); err != nil {
+	        t.Fatal(err)
+	}
+}

test/iptables/nat.go

@@ -0,0 +1,83 @@
+// Copyright 2019 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package iptables
+
+import (
+        "fmt"
+        "net"
+)
+
+const (
+        redirectPort     = 42
+)
+
+func init() {
+        RegisterTestCase(FilterNATRedirectUDPPort{})
+	RegisterTestCase(FilterNATDropUDP{})
+}
+
+// FilterInputRedirectUDPPort tests that packets are redirected to different port.
+type FilterNATRedirectUDPPort struct{}
+
+// Name implements TestCase.Name.
+func (FilterNATRedirectUDPPort) Name() string {
+        return "FilterNATRedirectUDPPort"
+}
+
+// ContainerAction implements TestCase.ContainerAction.
+func (FilterNATRedirectUDPPort) ContainerAction(ip net.IP) error {
+        if err := filterTable("-t", "nat", "-A", "PREROUTING", "-p", "udp", "-j", "REDIRECT", "--to-ports",
+	fmt.Sprintf("%d", redirectPort)); err != nil {
+		return err
+	}
+
+	if err := listenUDP(redirectPort, sendloopDuration); err != nil {
+	        return fmt.Errorf("packets on port %d should be allowed, but encountered an error: %v", redirectPort, err)
+	}
+
+	return nil
+}
+
+// LocalAction implements TestCase.LocalAction.
+func (FilterNATRedirectUDPPort) LocalAction(ip net.IP) error {
+        return sendUDPLoop(ip, acceptPort, sendloopDuration)
+}
+
+// FilterNATDropUDP tests that packets are not received in ports other than redirect port.
+type FilterNATDropUDP struct{}
+
+// Name implements TestCase.Name.
+func (FilterNATDropUDP) Name() string {
+        return "FilterNATDropUDP"
+}
+
+// ContainerAction implements TestCase.ContainerAction.
+func (FilterNATDropUDP) ContainerAction(ip net.IP) error {
+        if err := filterTable("-t", "nat", "-A", "PREROUTING", "-p", "udp", "-j", "REDIRECT", "--to-ports",
+	fmt.Sprintf("%d", redirectPort)); err != nil {
+		return err
+	}
+
+	if err := listenUDP(acceptPort, sendloopDuration); err == nil {
+		return fmt.Errorf("packets on port %d should have been redirected to port %d", acceptPort, redirectPort)
+	}
+
+	return nil
+}
+
+// LocalAction implements TestCase.LocalAction.
+func (FilterNATDropUDP) LocalAction(ip net.IP) error {
+        return sendUDPLoop(ip, acceptPort, sendloopDuration)
+}