Initial commit

Sources/DNSServer/DNSHandler.swift

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+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the container project authors. All rights reserved.
+//
+// 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.
+//===----------------------------------------------------------------------===//
+
+/// Protocol for implementing custom DNS handlers.
+public protocol DNSHandler {
+    /// Attempt to answer a DNS query
+    /// - Parameter query: the query message
+    /// - Throws: a server failure occurred during the query
+    /// - Returns: The response message for the query, or nil if the request
+    ///   is not within the scope of the handler.
+    func answer(query: Message) async throws -> Message?
+}

Sources/DNSServer/DNSServer+Handle.swift

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+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the container project authors. All rights reserved.
+//
+// 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.
+//===----------------------------------------------------------------------===//
+
+import Foundation
+import NIOCore
+import NIOPosix
+
+extension DNSServer {
+    /// Handles the DNS request.
+    /// - Parameters:
+    ///   - outbound: The NIOAsyncChannelOutboundWriter for which to respond.
+    ///   - packet: The request packet.
+    func handle(
+        outbound: NIOAsyncChannelOutboundWriter<AddressedEnvelope<ByteBuffer>>,
+        packet: inout AddressedEnvelope<ByteBuffer>
+    ) async throws {
+        let chunkSize = 512
+        var data = Data()
+
+        self.log?.debug("reading data")
+        while packet.data.readableBytes > 0 {
+            if let chunk = packet.data.readBytes(length: min(chunkSize, packet.data.readableBytes)) {
+                data.append(contentsOf: chunk)
+            }
+        }
+
+        self.log?.debug("deserializing message")
+        let query = try Message(deserialize: data)
+        self.log?.debug("processing query: \(query.questions)")
+
+        // always send response
+        let responseData: Data
+        do {
+            self.log?.debug("awaiting processing")
+            var response =
+                try await handler.answer(query: query)
+                ?? Message(
+                    id: query.id,
+                    type: .response,
+                    returnCode: .notImplemented,
+                    questions: query.questions,
+                    answers: []
+                )
+
+            // no responses
+            if response.answers.isEmpty {
+                response.returnCode = .nonExistentDomain
+            }
+
+            self.log?.debug("serializing response")
+            responseData = try response.serialize()
+        } catch {
+            self.log?.error("error processing message from \(query): \(error)")
+            let response = Message(
+                id: query.id,
+                type: .response,
+                returnCode: .notImplemented,
+                questions: query.questions,
+                answers: []
+            )
+            responseData = try response.serialize()
+        }
+
+        self.log?.debug("sending response for \(query.id)")
+        let rData = ByteBuffer(bytes: responseData)
+        try? await outbound.write(AddressedEnvelope(remoteAddress: packet.remoteAddress, data: rData))
+
+        self.log?.debug("processing done")
+
+    }
+}

Sources/DNSServer/DNSServer.swift

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+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the container project authors. All rights reserved.
+//
+// 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.
+//===----------------------------------------------------------------------===//
+
+import Foundation
+import Logging
+import NIOCore
+import NIOPosix
+
+/// Provides a DNS server.
+/// - Parameters:
+///   - host: The host address on which to listen.
+///   - port: The port for the server to listen.
+public struct DNSServer {
+    public var handler: DNSHandler
+    let log: Logger?
+
+    public init(
+        handler: DNSHandler,
+        log: Logger? = nil
+    ) {
+        self.handler = handler
+        self.log = log
+    }
+
+    public func run(host: String, port: Int) async throws {
+        // TODO: TCP server
+        let srv = try await DatagramBootstrap(group: NIOSingletons.posixEventLoopGroup)
+            .channelOption(.socketOption(.so_reuseaddr), value: 1)
+            .bind(host: host, port: port)
+            .flatMapThrowing { channel in
+                try NIOAsyncChannel(
+                    wrappingChannelSynchronously: channel,
+                    configuration: NIOAsyncChannel.Configuration(
+                        inboundType: AddressedEnvelope<ByteBuffer>.self,
+                        outboundType: AddressedEnvelope<ByteBuffer>.self
+                    )
+                )
+            }
+            .get()
+
+        try await srv.executeThenClose { inbound, outbound in
+            for try await var packet in inbound {
+                try await self.handle(outbound: outbound, packet: &packet)
+            }
+        }
+    }
+
+    public func run(socketPath: String) async throws {
+        // TODO: TCP server
+        let srv = try await DatagramBootstrap(group: NIOSingletons.posixEventLoopGroup)
+            .bind(unixDomainSocketPath: socketPath, cleanupExistingSocketFile: true)
+            .flatMapThrowing { channel in
+                try NIOAsyncChannel(
+                    wrappingChannelSynchronously: channel,
+                    configuration: NIOAsyncChannel.Configuration(
+                        inboundType: AddressedEnvelope<ByteBuffer>.self,
+                        outboundType: AddressedEnvelope<ByteBuffer>.self
+                    )
+                )
+            }
+            .get()
+
+        try await srv.executeThenClose { inbound, outbound in
+            for try await var packet in inbound {
+                log?.debug("received packet from \(packet.remoteAddress)")
+                try await self.handle(outbound: outbound, packet: &packet)
+                log?.debug("sent packet")
+            }
+        }
+    }
+
+    public func stop() async throws {}
+}

Sources/DNSServer/Handlers/CompositeResolver.swift

@@ -0,0 +1,34 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the container project authors. All rights reserved.
+//
+// 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.
+//===----------------------------------------------------------------------===//
+
+/// Delegates a query sequentially to handlers until one provides a response.
+public struct CompositeResolver: DNSHandler {
+    private let handlers: [DNSHandler]
+
+    public init(handlers: [DNSHandler]) {
+        self.handlers = handlers
+    }
+
+    public func answer(query: Message) async throws -> Message? {
+        for handler in self.handlers {
+            if let response = try await handler.answer(query: query) {
+                return response
+            }
+        }
+
+        return nil
+    }
+}

Sources/DNSServer/Handlers/HostTableResolver.swift

@@ -0,0 +1,83 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the container project authors. All rights reserved.
+//
+// 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.
+//===----------------------------------------------------------------------===//
+
+import DNS
+
+/// Handler that uses table lookup to resolve hostnames.
+public struct HostTableResolver: DNSHandler {
+    public let hosts4: [String: IPv4]
+    private let ttl: UInt32
+
+    public init(hosts4: [String: IPv4], ttl: UInt32 = 300) {
+        self.hosts4 = hosts4
+        self.ttl = ttl
+    }
+
+    public func answer(query: Message) async throws -> Message? {
+        let question = query.questions[0]
+        let record: ResourceRecord?
+        switch question.type {
+        case ResourceRecordType.host:
+            record = answerHost(question: question)
+        case ResourceRecordType.nameServer,
+            ResourceRecordType.alias,
+            ResourceRecordType.startOfAuthority,
+            ResourceRecordType.pointer,
+            ResourceRecordType.mailExchange,
+            ResourceRecordType.text,
+            ResourceRecordType.host6,
+            ResourceRecordType.service,
+            ResourceRecordType.incrementalZoneTransfer,
+            ResourceRecordType.standardZoneTransfer,
+            ResourceRecordType.all:
+            return Message(
+                id: query.id,
+                type: .response,
+                returnCode: .notImplemented,
+                questions: query.questions,
+                answers: []
+            )
+        default:
+            return Message(
+                id: query.id,
+                type: .response,
+                returnCode: .formatError,
+                questions: query.questions,
+                answers: []
+            )
+        }
+
+        guard let record else {
+            return nil
+        }
+
+        return Message(
+            id: query.id,
+            type: .response,
+            returnCode: .noError,
+            questions: query.questions,
+            answers: [record]
+        )
+    }
+
+    private func answerHost(question: Question) -> ResourceRecord? {
+        guard let ip = hosts4[question.name] else {
+            return nil
+        }
+
+        return HostRecord<IPv4>(name: question.name, ttl: ttl, ip: ip)
+    }
+}

Sources/DNSServer/Handlers/NxDomainResolver.swift

@@ -0,0 +1,66 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the container project authors. All rights reserved.
+//
+// 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.
+//===----------------------------------------------------------------------===//
+
+import DNS
+
+/// Handler that returns NXDOMAIN for all hostnames.
+public struct NxDomainResolver: DNSHandler {
+    private let ttl: UInt32
+
+    public init(ttl: UInt32 = 300) {
+        self.ttl = ttl
+    }
+
+    public func answer(query: Message) async throws -> Message? {
+        let question = query.questions[0]
+        switch question.type {
+        case ResourceRecordType.host:
+            return Message(
+                id: query.id,
+                type: .response,
+                returnCode: .nonExistentDomain,
+                questions: query.questions,
+                answers: []
+            )
+        case ResourceRecordType.nameServer,
+            ResourceRecordType.alias,
+            ResourceRecordType.startOfAuthority,
+            ResourceRecordType.pointer,
+            ResourceRecordType.mailExchange,
+            ResourceRecordType.text,
+            ResourceRecordType.host6,
+            ResourceRecordType.service,
+            ResourceRecordType.incrementalZoneTransfer,
+            ResourceRecordType.standardZoneTransfer,
+            ResourceRecordType.all:
+            return Message(
+                id: query.id,
+                type: .response,
+                returnCode: .notImplemented,
+                questions: query.questions,
+                answers: []
+            )
+        default:
+            return Message(
+                id: query.id,
+                type: .response,
+                returnCode: .formatError,
+                questions: query.questions,
+                answers: []
+            )
+        }
+    }
+}

Sources/DNSServer/Handlers/StandardQueryValidator.swift

@@ -0,0 +1,64 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the container project authors. All rights reserved.
+//
+// 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.
+//===----------------------------------------------------------------------===//
+
+/// Pass standard queries to a delegate handler.
+public struct StandardQueryValidator: DNSHandler {
+    private let handler: DNSHandler
+
+    /// Create the handler.
+    /// - Parameter delegate: the handler that receives valid queries
+    public init(handler: DNSHandler) {
+        self.handler = handler
+    }
+
+    /// Ensures the query is valid before forwarding it to the delegate.
+    /// - Parameter msg: the query message
+    /// - Returns: the delegate response if the query is valid, and an
+    ///   error response otherwise
+    public func answer(query: Message) async throws -> Message? {
+        // Reject response messages.
+        guard query.type == .query else {
+            return Message(
+                id: query.id,
+                type: .response,
+                returnCode: .formatError,
+                questions: query.questions
+            )
+        }
+
+        // Standard DNS servers handle only query operations.
+        guard query.operationCode == .query else {
+            return Message(
+                id: query.id,
+                type: .response,
+                returnCode: .notImplemented,
+                questions: query.questions
+            )
+        }
+
+        // Standard DNS servers only handle messages with exactly one question.
+        guard query.questions.count == 1 else {
+            return Message(
+                id: query.id,
+                type: .response,
+                returnCode: .formatError,
+                questions: query.questions
+            )
+        }
+
+        return try await handler.answer(query: query)
+    }
+}

Sources/DNSServer/Types.swift

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+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the container project authors. All rights reserved.
+//
+// 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.
+//===----------------------------------------------------------------------===//
+
+//
+
+import DNS
+import Foundation
+
+public typealias Message = DNS.Message
+public typealias ResourceRecord = DNS.ResourceRecord
+public typealias HostRecord = DNS.HostRecord
+public typealias IPv4 = DNS.IPv4
+public typealias IPv6 = DNS.IPv6
+public typealias ReturnCode = DNS.ReturnCode
+
+public enum DNSResolverError: Swift.Error, CustomStringConvertible {
+    case serverError(_ msg: String)
+    case invalidHandlerSpec(_ spec: String)
+    case unsupportedHandlerType(_ t: String)
+    case invalidIP(_ v: String)
+    case invalidHandlerOption(_ v: String)
+    case handlerConfigError(_ msg: String)
+
+    public var description: String {
+        switch self {
+        case .serverError(let msg):
+            return "server error: \(msg)"
+        case .invalidHandlerSpec(let msg):
+            return "invalid handler spec: \(msg)"
+        case .unsupportedHandlerType(let t):
+            return "unsupported handler type specified: \(t)"
+        case .invalidIP(let ip):
+            return "invalid IP specified: \(ip)"
+        case .invalidHandlerOption(let v):
+            return "invalid handler option specified: \(v)"
+        case .handlerConfigError(let msg):
+            return "error configuring handler: \(msg)"
+        }
+    }
+}