Add implementation and test for SetIPForwarding()

- Addressed Arnaud's comments

Signed-off-by: Alessandro Boch <aboch@socketplane.io>

libnetwork/drivers/bridge/setup.go

@@ -29,7 +29,3 @@ func (b *BridgeSetup) QueueStep(step SetupStep) {
 func SetupIPTables(i *Interface) error {
 	return nil
 }
-
-func SetupIPForwarding(i *Interface) error {
-	return nil
-}

libnetwork/drivers/bridge/setup_ip_forwarding.go

@@ -0,0 +1,20 @@
+package bridge
+
+import (
+	"fmt"
+	"io/ioutil"
+)
+
+const (
+	IPV4_FORW_CONF_FILE = "/proc/sys/net/ipv4/ip_forward"
+	PERM                = 0644
+)
+
+func SetupIPForwarding(i *Interface) error {
+	// Sanity Check
+	if i.Config.EnableIPForwarding == false {
+		return fmt.Errorf("Unexpected request to enable IP Forwarding for: %v", *i)
+	}
+	// Enable IPv4 forwarding
+	return ioutil.WriteFile(IPV4_FORW_CONF_FILE, []byte{'1', '\n'}, PERM)
+}

libnetwork/drivers/bridge/setup_ip_forwarding_test.go

@@ -0,0 +1,78 @@
+package bridge
+
+import (
+	"bytes"
+	"io/ioutil"
+	"testing"
+)
+
+func TestSetupIPForwarding(t *testing.T) {
+	// Read current setting and ensure the original value gets restored
+	procSetting := readCurrentIPForwardingSetting(t)
+	defer reconcileIPForwardingSetting(t, procSetting)
+
+	// Disable IP Forwarding if enabled
+	if bytes.Compare(procSetting, []byte("1\n")) == 0 {
+		writeIPForwardingSetting(t, []byte{'0', '\n'})
+	}
+
+	// Create test interface with ip forwarding setting enabled
+	br := &Interface{
+		Config: &Configuration{
+			BridgeName:         DefaultBridgeName,
+			EnableIPForwarding: true,
+		},
+	}
+
+	// Set IP Forwarding
+	if err := SetupIPForwarding(br); err != nil {
+		t.Fatalf("Failed to setup IP forwarding: %v", err)
+	}
+
+	// Read new setting
+	procSetting = readCurrentIPForwardingSetting(t)
+	if bytes.Compare(procSetting, []byte("1\n")) != 0 {
+		t.Fatalf("Failed to effectively setup IP forwarding")
+	}
+}
+
+func TestUnexpectedSetupIPForwarding(t *testing.T) {
+	// Read current setting and ensure the original value gets restored
+	procSetting := readCurrentIPForwardingSetting(t)
+	defer reconcileIPForwardingSetting(t, procSetting)
+
+	// Create test interface without ip forwarding setting enabled
+	br := &Interface{
+		Config: &Configuration{
+			BridgeName:         DefaultBridgeName,
+			EnableIPForwarding: false,
+		},
+	}
+
+	// Attempt Set IP Forwarding
+	if err := SetupIPForwarding(br); err == nil {
+		t.Fatalf(err.Error())
+	}
+}
+
+func readCurrentIPForwardingSetting(t *testing.T) []byte {
+	procSetting, err := ioutil.ReadFile(IPV4_FORW_CONF_FILE)
+	if err != nil {
+		t.Fatalf("Can't execute test: Failed to read current IP forwarding setting: %v", err)
+	}
+	return procSetting
+}
+
+func writeIPForwardingSetting(t *testing.T, chars []byte) {
+	err := ioutil.WriteFile(IPV4_FORW_CONF_FILE, chars, PERM)
+	if err != nil {
+		t.Fatalf("Can't execute or cleanup after test: Failed to reset IP forwarding: %v", err)
+	}
+}
+
+func reconcileIPForwardingSetting(t *testing.T, original []byte) {
+	current := readCurrentIPForwardingSetting(t)
+	if bytes.Compare(original, current) != 0 {
+		writeIPForwardingSetting(t, original)
+	}
+}