chore: import upstream snapshot with attribution

Sources/Containerization/NATNetworkInterface.swift

@@ -0,0 +1,84 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025-2026 Apple Inc. and the Containerization project 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
+//
+//   https://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.
+//===----------------------------------------------------------------------===//
+
+#if os(macOS)
+
+import vmnet
+import Virtualization
+import ContainerizationError
+import ContainerizationExtras
+import Synchronization
+
+/// An interface that uses NAT to provide an IP address for a given
+/// container/virtual machine.
+@available(macOS 26, *)
+public final class NATNetworkInterface: Interface, Sendable {
+    public let ipv4Address: CIDRv4
+    public let ipv4Gateway: IPv4Address?
+    public let macAddress: MACAddress?
+    public let mtu: UInt32
+
+    @available(macOS 26, *)
+    // `reference` isn't used concurrently.
+    public nonisolated(unsafe) let reference: vmnet_network_ref!
+
+    @available(macOS 26, *)
+    public init(
+        ipv4Address: CIDRv4,
+        ipv4Gateway: IPv4Address?,
+        reference: sending vmnet_network_ref,
+        macAddress: MACAddress? = nil,
+        mtu: UInt32 = 1500
+    ) {
+        self.ipv4Address = ipv4Address
+        self.ipv4Gateway = ipv4Gateway
+        self.macAddress = macAddress
+        self.mtu = mtu
+        self.reference = reference
+    }
+
+    @available(macOS, obsoleted: 26, message: "Use init(ipv4Address:ipv4Gateway:reference:macAddress:) instead")
+    public init(
+        ipv4Address: CIDRv4,
+        ipv4Gateway: IPv4Address?,
+        macAddress: MACAddress? = nil,
+        mtu: UInt32 = 1500
+    ) {
+        self.ipv4Address = ipv4Address
+        self.ipv4Gateway = ipv4Gateway
+        self.macAddress = macAddress
+        self.mtu = mtu
+        self.reference = nil
+    }
+}
+
+@available(macOS 26, *)
+extension NATNetworkInterface: VZInterface {
+    public func device() throws -> VZVirtioNetworkDeviceConfiguration {
+        let config = VZVirtioNetworkDeviceConfiguration()
+        if let macAddress = self.macAddress {
+            guard let mac = VZMACAddress(string: macAddress.description) else {
+                throw ContainerizationError(.invalidArgument, message: "invalid mac address \(macAddress)")
+            }
+            config.macAddress = mac
+        }
+
+        config.attachment = VZVmnetNetworkDeviceAttachment(network: self.reference)
+        return config
+    }
+}
+
+#endif