Add "strlen" extractionFn. (#3731)

docs/content/querying/dimensionspecs.md

@@ -150,9 +150,13 @@ matches, otherwise returns null.
 
 ### Substring Extraction Function
 
-Returns a substring of the dimension value starting from the supplied index and of the desired length. If the desired
-length exceeds the length of the dimension value, the remainder of the string starting at index will be returned. 
-If index is greater than the length of the dimension value, null will be returned.
+Returns a substring of the dimension value starting from the supplied index and of the desired length. Both index
+and length are measured in the number of Unicode code units present in the string as if it were encoded in UTF-16.
+Note that some Unicode characters may be represented by two code units. This is the same behavior as the Java String
+class's "substring" method.
+
+If the desired length exceeds the length of the dimension value, the remainder of the string starting at index will
+be returned. If index is greater than the length of the dimension value, null will be returned.
 
 ```json
 { "type" : "substring", "index" : 1, "length" : 4 }
@@ -165,6 +169,17 @@ or null if index greater than the length of the dimension value.
 { "type" : "substring", "index" : 3 }
 ```
 
+### Strlen Extraction Function
+
+Returns the length of dimension values, as measured in the number of Unicode code units present in the string as if it
+were encoded in UTF-16. Note that some Unicode characters may be represented by two code units. This is the same
+behavior as the Java String class's "length" method.
+
+null strings are considered as having zero length.
+
+```json
+{ "type" : "strlen" }
+```
 
 ### Time Format Extraction Function
 

processing/src/main/java/io/druid/query/extraction/ExtractionCacheHelper.java

@@ -38,4 +38,5 @@ public class ExtractionCacheHelper
   public static final byte CACHE_TYPE_ID_UPPER = 0xB;
   public static final byte CACHE_TYPE_ID_LOWER = 0xC;
   public static final byte CACHE_TYPE_ID_BUCKET = 0xD;
+  public static final byte CACHE_TYPE_ID_STRLEN = 0xE;
 }

processing/src/main/java/io/druid/query/extraction/ExtractionFn.java

@@ -42,7 +42,8 @@ import io.druid.query.lookup.RegisteredLookupExtractionFn;
     @JsonSubTypes.Type(name = "stringFormat", value = StringFormatExtractionFn.class),
     @JsonSubTypes.Type(name = "upper", value = UpperExtractionFn.class),
     @JsonSubTypes.Type(name = "lower", value = LowerExtractionFn.class),
-    @JsonSubTypes.Type(name = "bucket", value = BucketExtractionFn.class)
+    @JsonSubTypes.Type(name = "bucket", value = BucketExtractionFn.class),
+    @JsonSubTypes.Type(name = "strlen", value = StrlenExtractionFn.class)
 })
 /**
  * An ExtractionFn is a function that can be used to transform the values of a column (typically a dimension)

processing/src/main/java/io/druid/query/extraction/StrlenExtractionFn.java

@@ -0,0 +1,61 @@
+/*
+ * Licensed to Metamarkets Group Inc. (Metamarkets) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. Metamarkets 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 io.druid.query.extraction;
+
+import com.fasterxml.jackson.annotation.JsonCreator;
+
+public class StrlenExtractionFn extends DimExtractionFn
+{
+  private static final StrlenExtractionFn INSTANCE = new StrlenExtractionFn();
+
+  private StrlenExtractionFn()
+  {
+  }
+
+  @JsonCreator
+  public static StrlenExtractionFn instance()
+  {
+    return INSTANCE;
+  }
+
+  @Override
+  public String apply(String value)
+  {
+    return String.valueOf(value == null ? 0 : value.length());
+  }
+
+  @Override
+  public boolean preservesOrdering()
+  {
+    return false;
+  }
+
+  @Override
+  public ExtractionType getExtractionType()
+  {
+    return ExtractionType.MANY_TO_ONE;
+  }
+
+  @Override
+  public byte[] getCacheKey()
+  {
+    return new byte[]{ExtractionCacheHelper.CACHE_TYPE_ID_STRLEN};
+  }
+}

processing/src/test/java/io/druid/query/extraction/StrlenExtractionFnTest.java

@@ -0,0 +1,65 @@
+/*
+ * Licensed to Metamarkets Group Inc. (Metamarkets) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. Metamarkets 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 io.druid.query.extraction;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import io.druid.jackson.DefaultObjectMapper;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class StrlenExtractionFnTest
+{
+  @Test
+  public void testApply()
+  {
+    Assert.assertEquals("0", StrlenExtractionFn.instance().apply(null));
+    Assert.assertEquals("0", StrlenExtractionFn.instance().apply(""));
+    Assert.assertEquals("1", StrlenExtractionFn.instance().apply("x"));
+    Assert.assertEquals("3", StrlenExtractionFn.instance().apply("foo"));
+    Assert.assertEquals("3", StrlenExtractionFn.instance().apply("föo"));
+    Assert.assertEquals("2", StrlenExtractionFn.instance().apply("\uD83D\uDE02"));
+    Assert.assertEquals("1", StrlenExtractionFn.instance().apply(1));
+    Assert.assertEquals("2", StrlenExtractionFn.instance().apply(-1));
+  }
+
+  @Test
+  public void testGetCacheKey()
+  {
+    Assert.assertArrayEquals(StrlenExtractionFn.instance().getCacheKey(), StrlenExtractionFn.instance().getCacheKey());
+  }
+
+  @Test
+  public void testSerde() throws Exception
+  {
+    final ObjectMapper objectMapper = new DefaultObjectMapper();
+
+    final String json = "{ \"type\" : \"strlen\" }";
+
+    StrlenExtractionFn extractionFn = (StrlenExtractionFn) objectMapper.readValue(json, ExtractionFn.class);
+    StrlenExtractionFn extractionFnRoundTrip = (StrlenExtractionFn) objectMapper.readValue(
+        objectMapper.writeValueAsString(extractionFn),
+        ExtractionFn.class
+    );
+
+    // Should all actually be the same instance.
+    Assert.assertTrue(extractionFn == extractionFnRoundTrip);
+    Assert.assertTrue(extractionFn == StrlenExtractionFn.instance());
+  }
+}