chore: import upstream snapshot with attribution

Tests/DNSServerTests/HostTableResolverTest.swift

@@ -0,0 +1,180 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025-2026 Apple Inc. and the container 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.
+//===----------------------------------------------------------------------===//
+
+import ContainerizationExtras
+import Testing
+
+@testable import DNSServer
+
+struct HostTableResolverTest {
+    @Test func testEmptyQuestionsReturnsNil() async throws {
+        let ip = try IPv4Address("1.2.3.4")
+        let handler = try HostTableResolver(hosts4: ["foo.": ip])
+
+        let query = Message(id: UInt16(1), type: .query, questions: [])
+
+        let response = try await handler.answer(query: query)
+
+        #expect(nil == response)
+    }
+
+    @Test func testUnsupportedQuestionType() async throws {
+        let ip = try IPv4Address("1.2.3.4")
+        let handler = try HostTableResolver(hosts4: ["foo.": ip])
+
+        let query = Message(
+            id: UInt16(1),
+            type: .query,
+            questions: [
+                Question(name: "foo.", type: .mailExchange)
+            ])
+
+        let response = try await handler.answer(query: query)
+
+        #expect(.notImplemented == response?.returnCode)
+        #expect(1 == response?.id)
+        #expect(.response == response?.type)
+        #expect(1 == response?.questions.count)
+        #expect(0 == response?.answers.count)
+    }
+
+    @Test func testAAAAQueryReturnsNoDataWhenARecordExists() async throws {
+        let ip = try IPv4Address("1.2.3.4")
+        let handler = try HostTableResolver(hosts4: ["foo.": ip])
+
+        let query = Message(
+            id: UInt16(1),
+            type: .query,
+            questions: [
+                Question(name: "foo.", type: .host6)
+            ])
+
+        let response = try await handler.answer(query: query)
+
+        // AAAA queries should return NODATA (noError with empty answers) when A record exists
+        // to avoid musl libc issues where NXDOMAIN causes complete DNS resolution failure
+        #expect(.noError == response?.returnCode)
+        #expect(1 == response?.id)
+        #expect(.response == response?.type)
+        #expect(1 == response?.questions.count)
+        #expect(0 == response?.answers.count)
+    }
+
+    @Test func testAAAAQueryReturnsNilWhenHostDoesNotExist() async throws {
+        let ip = try IPv4Address("1.2.3.4")
+        let handler = try HostTableResolver(hosts4: ["foo.": ip])
+
+        let query = Message(
+            id: UInt16(1),
+            type: .query,
+            questions: [
+                Question(name: "bar.", type: .host6)
+            ])
+
+        let response = try await handler.answer(query: query)
+
+        // AAAA queries for non-existent hosts should return nil (which becomes NXDOMAIN)
+        #expect(nil == response)
+    }
+
+    @Test func testHostNotPresent() async throws {
+        let ip = try IPv4Address("1.2.3.4")
+        let handler = try HostTableResolver(hosts4: ["foo.": ip])
+
+        let query = Message(
+            id: UInt16(1),
+            type: .query,
+            questions: [
+                Question(name: "bar.", type: .host)
+            ])
+
+        let response = try await handler.answer(query: query)
+
+        #expect(nil == response)
+    }
+
+    @Test func testHostPresent() async throws {
+        let ip = try IPv4Address("1.2.3.4")
+        let handler = try HostTableResolver(hosts4: ["foo.": ip])
+
+        let query = Message(
+            id: UInt16(1),
+            type: .query,
+            questions: [
+                Question(name: "foo.", type: .host)
+            ])
+
+        let response = try await handler.answer(query: query)
+
+        #expect(.noError == response?.returnCode)
+        #expect(1 == response?.id)
+        #expect(.response == response?.type)
+        #expect(1 == response?.questions.count)
+        #expect("foo." == response?.questions[0].name)
+        #expect(.host == response?.questions[0].type)
+        #expect(1 == response?.answers.count)
+        let answer = response?.answers[0] as? HostRecord<IPv4Address>
+        #expect(try IPv4Address("1.2.3.4") == answer?.ip)
+    }
+
+    @Test func testHostPresentUppercaseTable() async throws {
+        let ip = try IPv4Address("1.2.3.4")
+        let handler = try HostTableResolver(hosts4: ["FOO.": ip])
+
+        let query = Message(
+            id: UInt16(1),
+            type: .query,
+            questions: [
+                Question(name: "foo.", type: .host)
+            ])
+
+        let response = try await handler.answer(query: query)
+
+        #expect(.noError == response?.returnCode)
+        #expect(1 == response?.id)
+        #expect(.response == response?.type)
+        #expect(1 == response?.questions.count)
+        #expect("foo." == response?.questions[0].name)
+        #expect(.host == response?.questions[0].type)
+        #expect(1 == response?.answers.count)
+        let answer = response?.answers[0] as? HostRecord<IPv4Address>
+        #expect(try IPv4Address("1.2.3.4") == answer?.ip)
+    }
+
+    @Test func testHostPresentUppercaseQuestion() async throws {
+        let ip = try IPv4Address("1.2.3.4")
+        let handler = try HostTableResolver(hosts4: ["foo.": ip])
+
+        let query = Message(
+            id: UInt16(1),
+            type: .query,
+            questions: [
+                Question(name: "FOO.", type: .host)
+            ])
+
+        let response = try await handler.answer(query: query)
+
+        #expect(.noError == response?.returnCode)
+        #expect(1 == response?.id)
+        #expect(.response == response?.type)
+        #expect(1 == response?.questions.count)
+        #expect("FOO." == response?.questions[0].name)
+        #expect(.host == response?.questions[0].type)
+        #expect(1 == response?.answers.count)
+        let answer = response?.answers[0] as? HostRecord<IPv4Address>
+        #expect(try IPv4Address("1.2.3.4") == answer?.ip)
+    }
+}