feat: add CHR UDF

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

@@ -382,6 +382,26 @@ include both endpoints.
 
 ## Strings
 
+### `CHR`
+
+```sql
+CHR(decimal_code | utf_string)
+```
+
+Returns a single-character string representing the Unicode code-point described by the input. The input parameter can be either a decimal character code or a string representation of a UTF code.
+
+Returns NULL if the input is NULL or does not represent a valid code-point.
+
+Commonly used to insert control characters such as ```Tab``` (9), ```Line Feed``` (10), or ```Carriage Return``` (13) into strings.
+
+Examples:
+```sql
+CHR(75)        => 'K'
+CHR('\u004b')  => 'K'
+CHR(22909)     => '好'
+CHR('\u597d')  => '好'
+```
+
 ### `CONCAT`
 
 ```sql

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

@@ -0,0 +1,48 @@
+/*
+ * 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;
+import io.confluent.ksql.function.udf.UdfParameter;
+import org.apache.commons.lang3.StringEscapeUtils;
+
+@UdfDescription(
+    name = "Chr",
+    description = "Returns a single-character string corresponding to the input character code.")
+public class Chr {
+
+  @Udf
+  public String chr(@UdfParameter(
+      description = "Decimal codepoint") final Integer decimalCode) {
+    if (decimalCode == null) {
+      return null;
+    }
+    if (!Character.isValidCodePoint(decimalCode)) {
+      return null;
+    }
+    final char[] resultChars = Character.toChars(decimalCode.intValue());
+    return String.valueOf(resultChars);
+  }
+
+  @Udf
+  public String chr(@UdfParameter(
+      description = "UTF16 code for the desired character e.g. '\\u004b'") final String utf16Code) {
+    if (utf16Code == null || utf16Code.length() < 6 || !utf16Code.startsWith("\\u")) {
+      return null;
+    }
+    return StringEscapeUtils.unescapeJava(utf16Code);
+  }
+}

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

@@ -0,0 +1,126 @@
+/*
+ * 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.CoreMatchers.is;
+import static org.hamcrest.CoreMatchers.nullValue;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+import org.junit.Test;
+
+public class ChrTest {
+  private final Chr udf = new Chr();
+
+  @Test
+  public void shouldConvertFromDecimal() {
+    final String result = udf.chr(75);
+    assertThat(result, is("K"));
+  }
+
+  @Test
+  public void shouldConvertFromUTF16String() {
+    final String result = udf.chr("\\u004b");
+    assertThat(result, is("K"));
+  }
+
+  @Test
+  public void shouldConvertFromUTF16StringWithSlash() {
+    final String result = udf.chr("\\u004b");
+    assertThat(result, is("K"));
+  }
+
+  @Test
+  public void shouldConvertZhFromDecimal() {
+    final String result = udf.chr(22909);
+    assertThat(result, is("好"));
+  }
+
+  @Test
+  public void shouldConvertZhFromUTF16() {
+    final String result = udf.chr("\\u597d");
+    assertThat(result, is("好"));
+  }
+
+  @Test
+  public void shouldConvertControlChar() {
+    final String result = udf.chr(9);
+    assertThat(result, is("\t"));
+  }
+
+  @Test
+  public void shouldReturnNullForNullIntegerInput() {
+    final String result = udf.chr((Integer) null);
+    assertThat(result, is(nullValue()));
+  }
+
+  @Test
+  public void shouldReturnNullForNullStringInput() {
+    final String result = udf.chr((String) null);
+    assertThat(result, is(nullValue()));
+  }
+
+  @Test
+  public void shouldReturnNullForEmptyStringInput() {
+    final String result = udf.chr("");
+    assertThat(result, is(nullValue()));
+  }
+
+  @Test
+  public void shouldReturnNullForNegativeDecimalCode() {
+    final String result = udf.chr(-1);
+    assertThat(result, is(nullValue()));
+  }
+
+  @Test
+  public void shouldReturnSingleCharForMaxBMPDecimal() {
+    final String result = udf.chr(65535);
+    assertThat(result.codePointAt(0), is(65535));
+    assertThat(result.toCharArray().length, is(1));
+  }
+
+  @Test
+  public void shouldReturnTwoCharsForNonBMPDecimal() {
+    final String result = udf.chr(65536);
+    assertThat(result.codePointAt(0), is(65536));
+    assertThat(result.toCharArray().length, is(2));
+  }
+
+  @Test
+  public void shouldReturnTwoCharsForMaxUnicodeDecimal() {
+    final String result = udf.chr(1_114_111);
+    assertThat(result.codePointAt(0), is(1_114_111));
+    assertThat(result.toCharArray().length, is(2));
+  }
+
+  @Test
+  public void shouldReturnNullForOutOfRangeDecimal() {
+    final String result = udf.chr(1_114_112);
+    assertThat(result, is(nullValue()));
+  }
+
+  @Test
+  public void shouldReturnNullForTooShortUTF16String() {
+    final String result = udf.chr("\\u065");
+    assertThat(result, is(nullValue()));
+  }
+
+  @Test
+  public void shouldReturnTwoCharsForNonBMPString() {
+    final String result = udf.chr("\\ud800\\udc01");
+    assertThat(result.codePointAt(0), is(65537));
+    assertThat(result.toCharArray().length, is(2));
+  }
+
+}

ksqldb-functional-tests/src/test/resources/historical_plans/chr_-_codepoint_from_decimal_code_-_AVRO/6.0.0_1591421496995/plan.json

@@ -0,0 +1,126 @@
+{
+  "plan" : [ {
+    "@type" : "ksqlPlanV1",
+    "statementText" : "CREATE STREAM INPUT (ID STRING KEY, UTFCODE INTEGER) WITH (KAFKA_TOPIC='test_topic', VALUE_FORMAT='AVRO');",
+    "ddlCommand" : {
+      "@type" : "createStreamV1",
+      "sourceName" : "INPUT",
+      "schema" : "`ID` STRING KEY, `UTFCODE` INTEGER",
+      "topicName" : "test_topic",
+      "formats" : {
+        "keyFormat" : {
+          "format" : "KAFKA"
+        },
+        "valueFormat" : {
+          "format" : "AVRO"
+        }
+      }
+    }
+  }, {
+    "@type" : "ksqlPlanV1",
+    "statementText" : "CREATE STREAM OUTPUT AS SELECT\n  INPUT.ID ID,\n  CHR(INPUT.UTFCODE) RESULT\nFROM INPUT INPUT\nEMIT CHANGES",
+    "ddlCommand" : {
+      "@type" : "createStreamV1",
+      "sourceName" : "OUTPUT",
+      "schema" : "`ID` STRING KEY, `RESULT` STRING",
+      "topicName" : "OUTPUT",
+      "formats" : {
+        "keyFormat" : {
+          "format" : "KAFKA"
+        },
+        "valueFormat" : {
+          "format" : "AVRO"
+        }
+      }
+    },
+    "queryPlan" : {
+      "sources" : [ "INPUT" ],
+      "sink" : "OUTPUT",
+      "physicalPlan" : {
+        "@type" : "streamSinkV1",
+        "properties" : {
+          "queryContext" : "OUTPUT"
+        },
+        "source" : {
+          "@type" : "streamSelectV1",
+          "properties" : {
+            "queryContext" : "Project"
+          },
+          "source" : {
+            "@type" : "streamSourceV1",
+            "properties" : {
+              "queryContext" : "KsqlTopic/Source"
+            },
+            "topicName" : "test_topic",
+            "formats" : {
+              "keyFormat" : {
+                "format" : "KAFKA"
+              },
+              "valueFormat" : {
+                "format" : "AVRO"
+              }
+            },
+            "sourceSchema" : "`ID` STRING KEY, `UTFCODE` INTEGER"
+          },
+          "keyColumnNames" : [ "ID" ],
+          "selectExpressions" : [ "CHR(UTFCODE) AS RESULT" ]
+        },
+        "formats" : {
+          "keyFormat" : {
+            "format" : "KAFKA"
+          },
+          "valueFormat" : {
+            "format" : "AVRO"
+          }
+        },
+        "topicName" : "OUTPUT"
+      },
+      "queryId" : "CSAS_OUTPUT_0"
+    }
+  } ],
+  "configs" : {
+    "ksql.extension.dir" : "ext",
+    "ksql.streams.cache.max.bytes.buffering" : "0",
+    "ksql.security.extension.class" : null,
+    "ksql.transient.prefix" : "transient_",
+    "ksql.persistence.wrap.single.values" : "true",
+    "ksql.authorization.cache.expiry.time.secs" : "30",
+    "ksql.schema.registry.url" : "",
+    "ksql.streams.default.deserialization.exception.handler" : "io.confluent.ksql.errors.LogMetricAndContinueExceptionHandler",
+    "ksql.output.topic.name.prefix" : "",
+    "ksql.streams.auto.offset.reset" : "earliest",
+    "ksql.query.pull.enable.standby.reads" : "false",
+    "ksql.connect.url" : "http://localhost:8083",
+    "ksql.service.id" : "some.ksql.service.id",
+    "ksql.internal.topic.min.insync.replicas" : "1",
+    "ksql.streams.shutdown.timeout.ms" : "300000",
+    "ksql.internal.topic.replicas" : "1",
+    "ksql.insert.into.values.enabled" : "true",
+    "ksql.query.pull.max.allowed.offset.lag" : "9223372036854775807",
+    "ksql.query.pull.max.qps" : "2147483647",
+    "ksql.streams.default.production.exception.handler" : "io.confluent.ksql.errors.ProductionExceptionHandlerUtil$LogAndFailProductionExceptionHandler",
+    "ksql.access.validator.enable" : "auto",
+    "ksql.streams.bootstrap.servers" : "localhost:0",
+    "ksql.streams.commit.interval.ms" : "2000",
+    "ksql.metric.reporters" : "",
+    "ksql.query.pull.metrics.enabled" : "false",
+    "ksql.streams.auto.commit.interval.ms" : "0",
+    "ksql.metrics.extension" : null,
+    "ksql.streams.topology.optimization" : "all",
+    "ksql.hidden.topics" : "_confluent.*,__confluent.*,_schemas,__consumer_offsets,__transaction_state,connect-configs,connect-offsets,connect-status,connect-statuses",
+    "ksql.streams.num.stream.threads" : "4",
+    "ksql.timestamp.throw.on.invalid" : "false",
+    "ksql.authorization.cache.max.entries" : "10000",
+    "ksql.metrics.tags.custom" : "",
+    "ksql.pull.queries.enable" : "true",
+    "ksql.udfs.enabled" : "true",
+    "ksql.udf.enable.security.manager" : "true",
+    "ksql.connect.worker.config" : "",
+    "ksql.sink.window.change.log.additional.retention" : "1000000",
+    "ksql.readonly.topics" : "_confluent.*,__confluent.*,_schemas,__consumer_offsets,__transaction_state,connect-configs,connect-offsets,connect-status,connect-statuses",
+    "ksql.udf.collect.metrics" : "false",
+    "ksql.persistent.prefix" : "query_",
+    "ksql.query.persistent.active.limit" : "2147483647",
+    "ksql.error.classifier.regex" : ""
+  }
+}