feat: new UUID UDF (#5535)

* new UUID UDF, first version

* match checkstyle class-naming rule

docs/developer-guide/ksqldb-reference/scalar-functions.md

@@ -561,6 +561,16 @@ UCASE(col1)
 
 Convert a string to uppercase.
 
+### `UUID`
+
+```sql
+UUID()
+```
+Create a Universally Unique Identifier (UUID) generated according to RFC 4122. 
+A call to UUID() returns a value conforming to UUID version 4, sometimes called 
+"random UUID", as described in RFC 4122. The value is a 128-bit number represented 
+as a string of five hexadecimal numbers _aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee_.
+
 ## Nulls
 
 ### `COALESCE`

ksqldb-engine/src/main/java/io/confluent/ksql/function/udf/string/Uuid.java

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2020 Confluent Inc.
+ *
+ * Licensed under the Confluent Community License (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.confluent.io/confluent-community-license
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License
+ * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and limitations under the
+ * License.
+ */
+
+package io.confluent.ksql.function.udf.string;
+
+import io.confluent.ksql.function.udf.Udf;
+import io.confluent.ksql.function.udf.UdfDescription;
+
+@UdfDescription(
+    name = "UUID",
+    description = "Create a Universally Unique Identifier (UUID) generated according to RFC 4122. "
+        + "A call to UUID() returns a value conforming to UUID version 4, sometimes called "
+        + "\"random UUID\", as described in RFC 4122. The value is a 128-bit number represented "
+        + "as a string of five hexadecimal numbers aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee.")
+public class Uuid {
+
+  @Udf
+  public String uuid() {
+    return java.util.UUID.randomUUID().toString();
+  }
+}

ksqldb-engine/src/test/java/io/confluent/ksql/function/udf/string/UuidTest.java

@@ -0,0 +1,62 @@
+/*
+ * Copyright 2020 Confluent Inc.
+ *
+ * Licensed under the Confluent Community License (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.confluent.io/confluent-community-license
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License
+ * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and limitations under the
+ * License.
+ */
+
+package io.confluent.ksql.function.udf.string;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.hasSize;
+import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.isIn;
+
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Set;
+import org.junit.Before;
+import org.junit.Test;
+
+public class UuidTest {
+
+  private Uuid udf;
+
+  @Before
+  public void setUp() {
+    udf = new Uuid();
+  }
+
+  @Test
+  public void shouldReturnDistinctValueEachInvocation() {
+    int capacity = 1000;
+    final Set<String> outputs = new HashSet<String>(capacity);
+    for (int i = 0; i < capacity; i++) {
+      outputs.add(udf.uuid());
+    }
+    assertThat(outputs, hasSize(capacity));
+  }
+
+  @Test
+  public void shouldHaveCorrectOutputFormat() {
+    // aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee
+    final String anUuid = udf.uuid();
+    assertThat(anUuid.length(), is(36));
+    assertThat(anUuid.charAt(8), is('-'));
+    assertThat(anUuid.charAt(13), is('-'));
+    assertThat(anUuid.charAt(18), is('-'));
+    assertThat(anUuid.charAt(23), is('-'));
+    for (final char c : anUuid.toCharArray()) {
+      assertThat(c, isIn(Arrays.asList('a', 'b', 'c', 'd', 'e', 'f', '1', '2', '3', '4', '5', '6',
+          '7', '8', '9', '0', '-')));
+    }
+  }
+
+}