Implement support for master interface configuration in CNI config

cni/cni.go

@@ -88,6 +88,7 @@ type NetworkConfig struct {
 	CniVersion       string           `json:"cniVersion"`
 	Name             string           `json:"name"` // Name is the Network Name.
 	Type             hcn.NetworkType  `json:"type"` // As per SPEC, Type is Name of the Binary
+	Master           string           `json:"master,omitempty"` // Host interface name to bind the network to
 	Ipam             IpamConfig       `json:"ipam"`
 	DNS              cniTypes.DNS     `json:"dns"`
 	OptionalFlags    OptionalFlags    `json:"optionalFlags"`
@@ -279,9 +280,14 @@ func (config *NetworkConfig) GetNetworkInfo(podNamespace string) (ninfo *network
 		Name:          config.Name,
 		Type:          config.Type,
 		Subnets:       subnets,
-		InterfaceName: "",
+		InterfaceName: config.Master,
 		DNS:           dnsSettings,
 	}
+
+	// Log when master interface is specified
+	if config.Master != "" {
+		logrus.Infof("[cni-net] Using master interface '%s' for network '%s'", config.Master, config.Name)
+	}
 	if config.AdditionalArgs != nil {
 		for _, kvp := range config.AdditionalArgs {
 			if strings.Contains(kvp.Name, "Policy") {

cni/cni_master_test.go

@@ -0,0 +1,86 @@
+// Copyright Microsoft Corp.
+// All rights reserved.
+
+//go:build windows
+// +build windows
+
+package cni
+
+import (
+	"testing"
+)
+
+// TestParseMasterField tests that the master field is properly parsed from CNI config
+func TestParseMasterField(t *testing.T) {
+	// Test with master field present
+	configWithMaster := `{
+		"cniVersion": "0.3.0",
+		"name": "testNetwork",
+		"type": "nat",
+		"master": "Ethernet",
+		"ipam": {
+			"subnet": "192.168.100.0/24"
+		}
+	}`
+
+	config, err := ParseNetworkConfig([]byte(configWithMaster))
+	if err != nil {
+		t.Fatalf("Failed to parse config with master field: %v", err)
+	}
+
+	if config.Master != "Ethernet" {
+		t.Errorf("Expected master to be 'Ethernet', got '%s'", config.Master)
+	}
+
+	// Test with master field missing (should be empty string)
+	configWithoutMaster := `{
+		"cniVersion": "0.3.0",
+		"name": "testNetwork",
+		"type": "nat",
+		"ipam": {
+			"subnet": "192.168.100.0/24"
+		}
+	}`
+
+	config2, err := ParseNetworkConfig([]byte(configWithoutMaster))
+	if err != nil {
+		t.Fatalf("Failed to parse config without master field: %v", err)
+	}
+
+	if config2.Master != "" {
+		t.Errorf("Expected master to be empty when not specified, got '%s'", config2.Master)
+	}
+}
+
+// TestMasterFieldInNetworkInfo tests that the master field is properly propagated to NetworkInfo
+func TestMasterFieldInNetworkInfo(t *testing.T) {
+	config := &NetworkConfig{
+		CniVersion: "0.3.0",
+		Name:       "testNetwork",
+		Type:       "nat",
+		Master:     "Ethernet",
+		Ipam: IpamConfig{
+			Subnet: "192.168.100.0/24",
+		},
+	}
+
+	networkInfo, err := config.GetNetworkInfo("")
+	if err != nil {
+		t.Fatalf("Failed to get network info: %v", err)
+	}
+
+	if networkInfo.InterfaceName != "Ethernet" {
+		t.Errorf("Expected InterfaceName to be 'Ethernet', got '%s'", networkInfo.InterfaceName)
+	}
+
+	// Test with empty master
+	config.Master = ""
+	networkInfo2, err := config.GetNetworkInfo("")
+	if err != nil {
+		t.Fatalf("Failed to get network info with empty master: %v", err)
+	}
+
+	if networkInfo2.InterfaceName != "" {
+		t.Errorf("Expected InterfaceName to be empty when master is empty, got '%s'", networkInfo2.InterfaceName)
+	}
+}