[ZEPPELIN-6484] Deduplicate IdHashes and add unit tests

zeppelin-interpreter/src/test/java/org/apache/zeppelin/util/IdHashesTest.java

@@ -0,0 +1,74 @@
+/*
+ * 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.
+ */
+
+package org.apache.zeppelin.util;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.HashSet;
+import java.util.Set;
+
+import org.junit.jupiter.api.Test;
+
+class IdHashesTest {
+
+  /**
+   * The characters generated IDs are expected to be built from: digits 1-9 and A-Z without
+   * I, L and O. Those three letters and the digit 0 are left out so that an ID stays
+   * unambiguous when a person reads it off a URL.
+   *
+   * <p>Spelled out here rather than read back from IdHashes so that changing the dictionary
+   * has to be a deliberate act that updates this test too.
+   */
+  private static final String EXPECTED_CHARACTERS = "123456789ABCDEFGHJKMNPQRSTUVWXYZ";
+
+  /**
+   * IDs are derived from {@code currentTimeMillis() + SecureRandom.nextInt()}, so uniqueness
+   * can only be asserted probabilistically. The random term spans 2^32 values, which puts the
+   * chance of a collision within one sample of this size on the order of 1e-4.
+   */
+  private static final int SAMPLE_SIZE = 1000;
+
+  @Test
+  void generatedIdsContainOnlyDictionaryCharacters() {
+    for (int i = 0; i < SAMPLE_SIZE; i++) {
+      String id = IdHashes.generateId();
+      for (char c : id.toCharArray()) {
+        assertTrue(EXPECTED_CHARACTERS.indexOf(c) >= 0,
+            "generated id '" + id + "' contains '" + c + "', which is not in the dictionary");
+      }
+    }
+  }
+
+  @Test
+  void generatedIdsAreNeverEmpty() {
+    for (int i = 0; i < SAMPLE_SIZE; i++) {
+      assertFalse(IdHashes.generateId().isEmpty(), "generateId() returned an empty id");
+    }
+  }
+
+  @Test
+  void generatedIdsAreDistinctAcrossManyCalls() {
+    Set<String> ids = new HashSet<>();
+    for (int i = 0; i < SAMPLE_SIZE; i++) {
+      ids.add(IdHashes.generateId());
+    }
+    assertEquals(SAMPLE_SIZE, ids.size(), "generateId() produced duplicate ids");
+  }
+}

zeppelin-server/src/main/java/org/apache/zeppelin/notebook/Note.java

@@ -36,11 +36,11 @@
 import org.apache.zeppelin.interpreter.remote.RemoteAngularObject;
 import org.apache.zeppelin.interpreter.remote.RemoteAngularObjectRegistry;
 import org.apache.zeppelin.interpreter.thrift.InterpreterCompletion;
-import org.apache.zeppelin.notebook.utility.IdHashes;
 import org.apache.zeppelin.scheduler.ExecutorFactory;
 import org.apache.zeppelin.scheduler.Job.Status;
 import org.apache.zeppelin.user.AuthenticationInfo;
 import org.apache.zeppelin.user.Credentials;
+import org.apache.zeppelin.util.IdHashes;
 import org.apache.zeppelin.util.Util;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;