Add a function to lookup nic by mac address and unit tests for NetworkAdapterPropertiesByMac and NetworkAdapterProperties

PiperOrigin-RevId: 784414281

go/network/w32iphelper.go

@@ -36,6 +36,37 @@ var (
 	procSetIPForwardEntry = modiphlpapi.NewProc("SetIpForwardEntry2") // Set IP forward entry
 )
 
+// NetworkAdapterPropertiesByMac returns the network adapter with the given mac address.
+func NetworkAdapterPropertiesByMac(naflags GAAFlags, macAddress string) (*windows.IpAdapterAddresses, error) {
+	var b []byte
+	// Recommended initial size: https://learn.microsoft.com/en-us/windows/win32/api/iphlpapi/nf-iphlpapi-getadaptersaddresses#remarks
+	l := uint32(15000)
+	for {
+		b = make([]byte, l)
+		// https://learn.microsoft.com/en-us/windows/win32/api/iphlpapi/nf-iphlpapi-getadaptersaddresses
+		err := windows.GetAdaptersAddresses(syscall.AF_UNSPEC, uint32(naflags), 0, (*windows.IpAdapterAddresses)(unsafe.Pointer(&b[0])), &l)
+		if err == nil {
+			if l == 0 {
+				return nil, nil
+			}
+			break
+		}
+		if err.(syscall.Errno) != syscall.ERROR_BUFFER_OVERFLOW {
+			return nil, os.NewSyscallError("getadaptersaddresses", err)
+		}
+		if l <= uint32(len(b)) {
+			return nil, os.NewSyscallError("getadaptersaddresses", err)
+		}
+	}
+	for aa := (*windows.IpAdapterAddresses)(unsafe.Pointer(&b[0])); aa != nil; aa = aa.Next {
+		mac := net.HardwareAddr(aa.PhysicalAddress[:aa.PhysicalAddressLength])
+		if mac.String() == macAddress {
+			return aa, nil
+		}
+	}
+	return nil, fmt.Errorf("no adapter with mac address %q found", macAddress)
+}
+
 // NetworkAdapterProperties returns the network adapter with the given name.
 func NetworkAdapterProperties(naflags GAAFlags, name string) (*windows.IpAdapterAddresses, error) {
 	var b []byte

go/network/w32iphelper_test.go

@@ -0,0 +1,125 @@
+// Copyright 2025 Google LLC
+//
+// 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 w32iphelper
+
+import (
+	"net"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"golang.org/x/sys/windows"
+)
+
+func TestNetworkAdapterPropertiesByMac(t *testing.T) {
+	adapters, err := ListLocalInterfaces(GAAFlagIncludeAllInterfaces)
+	if err != nil {
+		t.Fatalf("ListLocalInterfaces() failed: %v", err)
+	}
+	if len(adapters) == 0 {
+		t.Skip("No network adapters found on this system.")
+	}
+
+	// Use a known adapter mac from the test VM.
+	var adapterMAC string
+	for _, adapter := range adapters {
+		if adapter.PhysicalAddressLength > 0 {
+			mac := net.HardwareAddr(adapter.PhysicalAddress[:adapter.PhysicalAddressLength])
+			adapterMAC = mac.String()
+			break
+		}
+	}
+
+	if adapterMAC == "" {
+		t.Skip("No network adapters with a physical address found on this system.")
+	}
+
+	tests := []struct {
+		name    string
+		mac     string
+		wantErr bool
+	}{
+		{
+			name: "success",
+			mac:  adapterMAC,
+		},
+		{
+			name:    "failure",
+			mac:     "DE:AD:BE:EF:CA:FE",
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			adapter, err := NetworkAdapterPropertiesByMac(GAAFlagIncludeAllInterfaces, tt.mac)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("NetworkAdapterPropertiesByMac() error = %v, wantErr = %v", err, tt.wantErr)
+				return
+			}
+			if tt.wantErr {
+				return // Expected error, nothing more to check.
+			}
+			mac := net.HardwareAddr(adapter.PhysicalAddress[:adapter.PhysicalAddressLength])
+			if diff := cmp.Diff(tt.mac, mac.String()); diff != "" {
+				t.Errorf("NetworkAdapterPropertiesByMac(%q) returned diff (-want +got):\n%s", tt.mac, diff)
+			}
+		})
+	}
+}
+
+func TestNetworkAdapterProperties(t *testing.T) {
+	adapters, err := ListLocalInterfaces(GAAFlagIncludeAllInterfaces)
+	if err != nil {
+		t.Fatalf("ListLocalInterfaces() failed: %v", err)
+	}
+	if len(adapters) == 0 {
+		t.Skip("No network adapters found on this system.")
+	}
+
+	// Use a known adapter name from the test VM
+	adapterName := windows.BytePtrToString(adapters[0].AdapterName)
+
+	tests := []struct {
+		name    string
+		adapter string
+		wantErr bool
+	}{
+		{
+			name:    "success",
+			adapter: adapterName,
+		},
+		{
+			name:    "failure",
+			adapter: "the-nic-is-a-lie",
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			adapter, err := NetworkAdapterProperties(GAAFlagIncludeAllInterfaces, tt.adapter)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("NetworkAdapterProperties() error = %v, wantErr = %v", err, tt.wantErr)
+				return
+			}
+			if tt.wantErr {
+				return // Expected error, nothing more to check.
+			}
+			if diff := cmp.Diff(tt.adapter, windows.BytePtrToString(adapter.AdapterName)); diff != "" {
+				t.Errorf("NetworkAdapterProperties(%q) returned diff (-want +got):\n%s", tt.adapter, diff)
+			}
+		})
+	}
+}