MultiMap (#34)

Co-authored-by: Tilmann Zäschke <tilmann.zaeschke@inf.ethz.ch>

CHANGELOG.md

@@ -25,6 +25,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
   [#22](https://github.com/netsec-ethz/scion-java-client/pull/22)
 - BREAKING CHANGE: `getCurrentPath()` renamed to `getConnectionPath()`
   [#30](https://github.com/netsec-ethz/scion-java-client/pull/30)
+- Cleaned up `MultiMap` utility class 
+  [#34](https://github.com/netsec-ethz/scion-java-client/pull/34)
 
 ### Fixed
 - Fixed: SCMP problem when pinging local AS.

src/main/java/org/scion/internal/MultiMap.java

@@ -20,30 +20,18 @@ public class MultiMap<K, V> {
   private final HashMap<K, ArrayList<V>> map = new HashMap<>();
 
   public void put(K key, V value) {
-    ArrayList<V> entry = map.get(key);
-    if (entry == null) {
-      entry = new ArrayList<>();
-      map.put(key, entry);
-    }
-    entry.add(value);
+    map.computeIfAbsent(key, k -> new ArrayList<>()).add(value);
   }
 
-  public ArrayList<V> get(K key) {
-    return map.get(key);
+  public List<V> get(K key) {
+    ArrayList<V> result = map.get(key);
+    return result == null ? Collections.emptyList() : result;
   }
 
   public boolean contains(K key) {
     return map.containsKey(key);
   }
 
-  public Set<Map.Entry<K, ArrayList<V>>> entrySet() {
-    return map.entrySet();
-  }
-
-  public Collection<ArrayList<V>> values() {
-    return map.values();
-  }
-
   public boolean isEmpty() {
     return map.isEmpty();
   }

src/main/java/org/scion/internal/Segments.java

@@ -239,11 +239,8 @@ private static List<Daemon.Path> combineTwoSegments(
     List<Daemon.Path> paths = new ArrayList<>();
     for (Seg.PathSegment pathSegment0 : segments0) {
       long middleIsdAs = getOtherIsdAs(srcIsdAs, pathSegment0);
-      ArrayList<Seg.PathSegment> segmentList1 = segmentsMap1.get(middleIsdAs);
-      if (segmentList1 != null) {
-        for (Seg.PathSegment pathSegment1 : segmentList1) {
-          paths.add(buildPath(brLookup, pathSegment0, pathSegment1));
-        }
+      for (Seg.PathSegment pathSegment1 : segmentsMap1.get(middleIsdAs)) {
+        paths.add(buildPath(brLookup, pathSegment0, pathSegment1));
       }
     }
     return paths;
@@ -263,9 +260,9 @@ private static List<Daemon.Path> combineThreeSegments(
     List<Daemon.Path> paths = new ArrayList<>();
     for (Seg.PathSegment pathSeg : segmentsCore) {
       long[] endIAs = getEndingIAs(pathSeg);
-      if (upSegments.get(endIAs[0]) != null && downSegments.get(endIAs[1]) != null) {
+      if (upSegments.contains(endIAs[0]) && downSegments.contains(endIAs[1])) {
         buildPath(paths, upSegments.get(endIAs[0]), pathSeg, downSegments.get(endIAs[1]), brLookup);
-      } else if (upSegments.get(endIAs[1]) != null && downSegments.get(endIAs[0]) != null) {
+      } else if (upSegments.contains(endIAs[1]) && downSegments.contains(endIAs[0])) {
         buildPath(paths, upSegments.get(endIAs[1]), pathSeg, downSegments.get(endIAs[0]), brLookup);
       }
     }

src/test/java/org/scion/internal/MultiMapTest.java

@@ -0,0 +1,84 @@
+// Copyright 2024 ETH Zurich
+//
+// 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
+//
+//   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.
+
+package org.scion.internal;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.util.ArrayList;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+class MultiMapTest {
+
+  private static class Pair {
+    int i;
+    String s;
+
+    Pair(int i, String s) {
+      this.i = i;
+      this.s = s;
+    }
+  }
+
+  @Test
+  void testSmoke() {
+    MultiMap<Integer, String> map = new MultiMap<>();
+    ArrayList<Pair> list = new ArrayList<>();
+    for (int i = 0; i < 1000; i++) {
+      // Use duplicate keys as well as duplicate values
+      Pair p = new Pair(i % 10, Integer.toString(i % 100));
+      map.put(p.i, p.s);
+      list.add(p);
+    }
+
+    assertFalse(map.isEmpty());
+
+    for (Pair p : list) {
+      assertTrue(map.contains(p.i));
+      List<String> entries = map.get(p.i);
+      assertEquals(100, entries.size());
+      int matches = 0;
+      int identity = 0;
+      for (String s : entries) {
+        assertEquals(p.i, Integer.parseInt(s) % 10);
+        if (p.s.equals(s)) {
+          matches++;
+        }
+        if (p.s == s) {
+          identity++;
+        }
+      }
+      assertEquals(10, matches);
+      assertEquals(1, identity);
+    }
+
+    map.clear();
+    assertTrue(map.isEmpty());
+    assertFalse(map.contains(0));
+    assertNotNull(map.get(0));
+    assertTrue(map.get(0).isEmpty());
+  }
+
+  @Test
+  void testEmptyMap() {
+    // Check that basic function don´t fail on empty map
+    MultiMap<Integer, String> map = new MultiMap<>();
+    assertTrue(map.isEmpty());
+    // assertEquals(0, map.size());
+    assertFalse(map.contains(0));
+    assertNotNull(map.get(0));
+    assertTrue(map.get(0).isEmpty());
+  }
+}