Network: Move to standalone type (#584)

The network protocol and VMNetNetwork implementation currently are
housed on ContainerManager even though they are generally useful types
even outside of this easy to use helper type. This change moves them to
not be nested types anymore, as well as exposes a new param on
VMNetNetworks constructor so we can pass the type of network.

Author: dcantah

Sources/Containerization/ContainerManager.swift

@@ -24,7 +24,6 @@ import Foundation
 import ContainerizationExtras
 import SystemPackage
 import Virtualization
-import vmnet
 
 /// A manager for creating and running containers.
 /// Supports container networking options.
@@ -37,184 +36,6 @@ public struct ContainerManager: Sendable {
         self.imageStore.path.appendingPathComponent("containers")
     }
 
-    /// A network that can allocate and release interfaces for use with containers.
-    public protocol Network: Sendable {
-        mutating func create(_ id: String) throws -> Interface?
-        mutating func release(_ id: String) throws
-    }
-
-    /// A network backed by vmnet on macOS.
-    @available(macOS 26.0, *)
-    public struct VmnetNetwork: Network {
-        private var allocator: Allocator
-        // `reference` isn't used concurrently.
-        nonisolated(unsafe) private let reference: vmnet_network_ref
-
-        /// The IPv4 subnet of this network.
-        public let subnet: CIDRv4
-
-        /// The IPv4 gateway address of this network.
-        public var ipv4Gateway: IPv4Address {
-            subnet.gateway
-        }
-
-        struct Allocator: Sendable {
-            private let addressAllocator: any AddressAllocator<UInt32>
-            private let cidr: CIDRv4
-            private var allocations: [String: UInt32]
-
-            init(cidr: CIDRv4) throws {
-                self.cidr = cidr
-                self.allocations = .init()
-                let size = Int(cidr.upper.value - cidr.lower.value - 3)
-                self.addressAllocator = try UInt32.rotatingAllocator(
-                    lower: cidr.lower.value + 2,
-                    size: UInt32(size)
-                )
-            }
-
-            mutating func allocate(_ id: String) throws -> CIDRv4 {
-                if allocations[id] != nil {
-                    throw ContainerizationError(.exists, message: "allocation with id \(id) already exists")
-                }
-                let index = try addressAllocator.allocate()
-                allocations[id] = index
-                let ip = IPv4Address(index)
-                return try CIDRv4(ip, prefix: cidr.prefix)
-            }
-
-            mutating func release(_ id: String) throws {
-                if let index = self.allocations[id] {
-                    try addressAllocator.release(index)
-                    allocations.removeValue(forKey: id)
-                }
-            }
-        }
-
-        /// A network interface supporting the vmnet_network_ref.
-        public struct Interface: Containerization.Interface, VZInterface, Sendable {
-            public let ipv4Address: CIDRv4
-            public let ipv4Gateway: IPv4Address?
-            public let macAddress: MACAddress?
-            public let mtu: UInt32
-
-            // `reference` isn't used concurrently.
-            nonisolated(unsafe) private let reference: vmnet_network_ref
-
-            public init(
-                reference: vmnet_network_ref,
-                ipv4Address: CIDRv4,
-                ipv4Gateway: IPv4Address,
-                macAddress: MACAddress? = nil,
-                mtu: UInt32 = 1500
-            ) {
-                self.ipv4Address = ipv4Address
-                self.ipv4Gateway = ipv4Gateway
-                self.macAddress = macAddress
-                self.mtu = mtu
-                self.reference = reference
-            }
-
-            /// Returns the underlying `VZVirtioNetworkDeviceConfiguration`.
-            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
-            }
-        }
-
-        /// Creates a new network.
-        /// - Parameter subnet: The subnet to use for this network.
-        public init(subnet: CIDRv4? = nil) throws {
-            var status: vmnet_return_t = .VMNET_FAILURE
-            guard let config = vmnet_network_configuration_create(.VMNET_SHARED_MODE, &status) else {
-                throw ContainerizationError(.unsupported, message: "failed to create vmnet config with status \(status)")
-            }
-
-            vmnet_network_configuration_disable_dhcp(config)
-
-            if let subnet {
-                try Self.configureSubnet(config, subnet: subnet)
-            }
-
-            guard let ref = vmnet_network_create(config, &status), status == .VMNET_SUCCESS else {
-                throw ContainerizationError(.unsupported, message: "failed to create vmnet network with status \(status)")
-            }
-
-            let cidr = try Self.getSubnet(ref)
-
-            self.allocator = try .init(cidr: cidr)
-            self.subnet = cidr
-            self.reference = ref
-        }
-
-        /// Returns a new interface for use with a container.
-        /// - Parameter id: The container ID.
-        public mutating func create(_ id: String) throws -> Containerization.Interface? {
-            let ipv4Address = try allocator.allocate(id)
-            return Self.Interface(
-                reference: self.reference,
-                ipv4Address: ipv4Address,
-                ipv4Gateway: self.ipv4Gateway,
-            )
-        }
-
-        /// Returns a new interface for use with a container with a custom MTU.
-        /// - Parameters:
-        ///   - id: The container ID.
-        ///   - mtu: The MTU for the interface.
-        public mutating func create(_ id: String, mtu: UInt32) throws -> Containerization.Interface? {
-            let ipv4Address = try allocator.allocate(id)
-            return Self.Interface(
-                reference: self.reference,
-                ipv4Address: ipv4Address,
-                ipv4Gateway: self.ipv4Gateway,
-                mtu: mtu
-            )
-        }
-
-        /// Performs cleanup of an interface.
-        /// - Parameter id: The container ID.
-        public mutating func release(_ id: String) throws {
-            try allocator.release(id)
-        }
-
-        private static func getSubnet(_ ref: vmnet_network_ref) throws -> CIDRv4 {
-            var subnet = in_addr()
-            var mask = in_addr()
-            vmnet_network_get_ipv4_subnet(ref, &subnet, &mask)
-
-            let sa = UInt32(bigEndian: subnet.s_addr)
-            let mv = UInt32(bigEndian: mask.s_addr)
-
-            let lower = IPv4Address(sa & mv)
-            let upper = IPv4Address(lower.value + ~mv)
-
-            return try CIDRv4(lower: lower, upper: upper)
-        }
-
-        private static func configureSubnet(_ config: vmnet_network_configuration_ref, subnet: CIDRv4) throws {
-            let gateway = subnet.gateway
-
-            var ga = in_addr()
-            inet_pton(AF_INET, gateway.description, &ga)
-
-            let mask = IPv4Address(subnet.prefix.prefixMask32)
-            var ma = in_addr()
-            inet_pton(AF_INET, mask.description, &ma)
-
-            guard vmnet_network_configuration_set_ipv4_subnet(config, &ga, &ma) == .VMNET_SUCCESS else {
-                throw ContainerizationError(.internalError, message: "failed to set subnet \(subnet) for network")
-            }
-        }
-    }
-
     /// Create a new manager with the provided kernel, initfs mount, image store
     /// and optional network implementation. This will use a Virtualization.framework
     /// backed VMM implicitly.
@@ -475,7 +296,7 @@ public struct ContainerManager: Sendable {
             if let imageConfig {
                 config.process = .init(from: imageConfig)
             }
-            if networking, let interface = try self.network?.create(id) {
+            if networking, let interface = try self.network?.createInterface(id) {
                 config.interfaces = [interface]
                 guard let gateway = interface.ipv4Gateway else {
                     throw ContainerizationError(
@@ -494,7 +315,7 @@ public struct ContainerManager: Sendable {
     ///
     /// - Parameter id: The container ID.
     public mutating func releaseNetwork(_ id: String) throws {
-        try self.network?.release(id)
+        try self.network?.releaseInterface(id)
     }
 
     /// Releases network resources and removes all files for a container.

Sources/Containerization/Network.swift

@@ -0,0 +1,21 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 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.
+//===----------------------------------------------------------------------===//
+
+/// A network that can allocate and release interfaces for use with containers.
+public protocol Network: Sendable {
+    mutating func createInterface(_ id: String) throws -> Interface?
+    mutating func releaseInterface(_ id: String) throws
+}