Apply RFC 6724 destination ordering and family preferences to DNS results.

Tighten resolver semantics and filtering for HTTP/TCP connect targets.

Author: arturobernalg

httpclient5-testing/src/test/java/org/apache/hc/client5/testing/AddressSelectingDnsResolverIT.java

@@ -0,0 +1,254 @@
+/*
+ * ====================================================================
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ * ====================================================================
+ *
+ * This software consists of voluntary contributions made by many
+ * individuals on behalf of the Apache Software Foundation.  For more
+ * information on the Apache Software Foundation, please see
+ * <http://www.apache.org/>.
+ *
+ */
+
+package org.apache.hc.client5.testing;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.net.Inet6Address;
+import java.net.InetAddress;
+import java.net.UnknownHostException;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import org.apache.hc.client5.http.AddressSelectingDnsResolver;
+import org.apache.hc.client5.http.DnsResolver;
+import org.apache.hc.client5.http.SystemDefaultDnsResolver;
+import org.apache.hc.client5.http.config.ProtocolFamilyPreference;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.EnabledIfSystemProperty;
+
+@EnabledIfSystemProperty(named = "httpclient.rfc6724.it", matches = "true")
+class AddressSelectingDnsResolverIT {
+
+    private static final String PROP_HOST = "httpclient.rfc6724.host";
+
+    @Test
+    void interleave_isStableInterleavingOfDefault_forSameResolution() throws Exception {
+        final String host = System.getProperty(PROP_HOST, "localhost");
+
+        final InetAddress[] resolvedOnce = SystemDefaultDnsResolver.INSTANCE.resolve(host);
+
+        final DnsResolver captured = new DnsResolver() {
+            @Override
+            public InetAddress[] resolve(final String h) throws UnknownHostException {
+                if (!host.equals(h)) {
+                    throw new UnknownHostException(h);
+                }
+                return resolvedOnce.clone();
+            }
+
+            @Override
+            public String resolveCanonicalHostname(final String h) throws UnknownHostException {
+                return SystemDefaultDnsResolver.INSTANCE.resolveCanonicalHostname(h);
+            }
+        };
+
+        final AddressSelectingDnsResolver rDefault =
+                new AddressSelectingDnsResolver(captured, ProtocolFamilyPreference.DEFAULT);
+
+        final AddressSelectingDnsResolver rInterleave =
+                new AddressSelectingDnsResolver(captured, ProtocolFamilyPreference.INTERLEAVE);
+
+        final InetAddress[] outDefault = rDefault.resolve(host);
+        final InetAddress[] outInterleave = rInterleave.resolve(host);
+
+        // 0) Both outputs must be permutations of the captured, single resolution.
+        Assertions.assertNotNull(outDefault);
+        assertSameElements(Arrays.asList(resolvedOnce), Arrays.asList(outDefault));
+        Assertions.assertNotNull(outInterleave);
+        assertSameElements(Arrays.asList(resolvedOnce), Arrays.asList(outInterleave));
+
+        // 1) Same elements between DEFAULT and INTERLEAVE (no drops, no additions).
+        assertSameElements(Arrays.asList(outDefault), Arrays.asList(outInterleave));
+
+        // 2) Family counts must match between DEFAULT and INTERLEAVE.
+        final Counts cDefault = countFamilies(outDefault);
+        final Counts cInterleave = countFamilies(outInterleave);
+        assertEquals(cDefault.v4, cInterleave.v4);
+        assertEquals(cDefault.v6, cInterleave.v6);
+
+        // 3) INTERLEAVE must be the stable interleaving of the DEFAULT-ordered list.
+        final List<InetAddress> expected = expectedInterleaveFromBaseline(Arrays.asList(outDefault));
+        assertEquals(expected, Arrays.asList(outInterleave));
+
+        // 4) If both families are present, the first 2*min(v4,v6) addresses must alternate by family.
+        final int pairs = Math.min(cInterleave.v4, cInterleave.v6);
+        if (pairs > 0) {
+            assertAlternatingPrefix(outInterleave, 2 * pairs);
+        }
+
+        // 5) Relative order within each family is preserved from DEFAULT.
+        assertFamilyRelativeOrderPreserved(outDefault, outInterleave);
+
+        // Diagnostics for manual runs.
+        System.out.println("Host: " + host);
+        dump("DEFAULT", outDefault);
+        dump("INTERLEAVE", outInterleave);
+    }
+
+    private static void assertSameElements(final List<InetAddress> a, final List<InetAddress> b) {
+        assertEquals(a.size(), b.size());
+
+        final List<InetAddress> remaining = new ArrayList<>(b);
+        for (final InetAddress x : a) {
+            assertTrue(remaining.remove(x), "Missing address: " + x);
+        }
+        assertTrue(remaining.isEmpty(), "Extra addresses: " + remaining);
+    }
+
+    private static final class Counts {
+        final int v4;
+        final int v6;
+
+        Counts(final int v4, final int v6) {
+            this.v4 = v4;
+            this.v6 = v6;
+        }
+    }
+
+    private static Counts countFamilies(final InetAddress[] out) {
+        int v4 = 0;
+        int v6 = 0;
+        for (final InetAddress a : out) {
+            if (a instanceof Inet6Address) {
+                v6++;
+            } else {
+                v4++;
+            }
+        }
+        return new Counts(v4, v6);
+    }
+
+    private static void assertAlternatingPrefix(final InetAddress[] out, final int length) {
+        if (length <= 1) {
+            return;
+        }
+        final boolean firstV6 = out[0] instanceof Inet6Address;
+        for (int i = 0; i < length; i++) {
+            final boolean expectV6 = firstV6 == (i % 2 == 0);
+            final boolean isV6 = out[i] instanceof Inet6Address;
+            assertEquals(expectV6, isV6, "Not alternating at index " + i);
+        }
+    }
+
+    private static void assertFamilyRelativeOrderPreserved(
+            final InetAddress[] base,
+            final InetAddress[] interleaved) {
+
+        final List<InetAddress> baseV6 = new ArrayList<>();
+        final List<InetAddress> baseV4 = new ArrayList<>();
+        for (final InetAddress a : base) {
+            if (a instanceof Inet6Address) {
+                baseV6.add(a);
+            } else {
+                baseV4.add(a);
+            }
+        }
+
+        final List<InetAddress> gotV6 = new ArrayList<>();
+        final List<InetAddress> gotV4 = new ArrayList<>();
+        for (final InetAddress a : interleaved) {
+            if (a instanceof Inet6Address) {
+                gotV6.add(a);
+            } else {
+                gotV4.add(a);
+            }
+        }
+
+        assertEquals(baseV6, gotV6, "IPv6 relative order changed");
+        assertEquals(baseV4, gotV4, "IPv4 relative order changed");
+    }
+
+    private static List<InetAddress> expectedInterleaveFromBaseline(final List<InetAddress> baseline) {
+        if (baseline.size() <= 1) {
+            return baseline;
+        }
+
+        final List<InetAddress> v6 = new ArrayList<>();
+        final List<InetAddress> v4 = new ArrayList<>();
+
+        for (final InetAddress a : baseline) {
+            if (a instanceof Inet6Address) {
+                v6.add(a);
+            } else {
+                v4.add(a);
+            }
+        }
+
+        if (v6.isEmpty() || v4.isEmpty()) {
+            return baseline;
+        }
+
+        final boolean startV6 = baseline.get(0) instanceof Inet6Address;
+
+        final List<InetAddress> out = new ArrayList<>(baseline.size());
+        int i6 = 0;
+        int i4 = 0;
+
+        while (i6 < v6.size() || i4 < v4.size()) {
+            if (startV6) {
+                if (i6 < v6.size()) {
+                    out.add(v6.get(i6++));
+                }
+                if (i4 < v4.size()) {
+                    out.add(v4.get(i4++));
+                }
+            } else {
+                if (i4 < v4.size()) {
+                    out.add(v4.get(i4++));
+                }
+                if (i6 < v6.size()) {
+                    out.add(v6.get(i6++));
+                }
+            }
+        }
+
+        return out;
+    }
+
+    private static void dump(final String label, final InetAddress[] out) {
+        int v4 = 0;
+        int v6 = 0;
+
+        System.out.println("Preference: " + label);
+        for (final InetAddress a : out) {
+            if (a instanceof Inet6Address) {
+                v6++;
+                System.out.println("  IPv6 " + a.getHostAddress());
+            } else {
+                v4++;
+                System.out.println("  IPv4 " + a.getHostAddress());
+            }
+        }
+        System.out.println("Counts: IPv4=" + v4 + " IPv6=" + v6);
+        System.out.println();
+    }
+}