EscapeJson function added to expression-language

Made use of org.apache.commons.lang3.StringEscapeUtils to do that
actual processing

Signed-off-by: Matt Burgess <mattyb149@apache.org>

nifi-commons/nifi-expression-language/src/main/antlr3/org/apache/nifi/attribute/expression/language/antlr/AttributeExpressionLexer.g

@@ -117,6 +117,7 @@ URL_DECODE : 'urlDecode';
 NOT : 'not';
 COUNT : 'count';
 RANDOM : 'random';
+ESCAPE_JSON : 'escapeJson';
 
 // 1 arg functions
 SUBSTRING_AFTER	: 'substringAfter';

nifi-commons/nifi-expression-language/src/main/antlr3/org/apache/nifi/attribute/expression/language/antlr/AttributeExpressionParser.g

@@ -73,7 +73,7 @@ tokens {
 }
 
 // functions that return Strings
-zeroArgString : (TO_UPPER | TO_LOWER | TRIM | TO_STRING | URL_ENCODE | URL_DECODE) LPAREN! RPAREN!;
+zeroArgString : (TO_UPPER | TO_LOWER | TRIM | TO_STRING | URL_ENCODE | URL_DECODE | ESCAPE_JSON) LPAREN! RPAREN!;
 oneArgString : ((SUBSTRING_BEFORE | SUBSTRING_BEFORE_LAST | SUBSTRING_AFTER | SUBSTRING_AFTER_LAST | REPLACE_NULL | REPLACE_EMPTY |
 				PREPEND | APPEND | FORMAT | STARTS_WITH | ENDS_WITH | CONTAINS | JOIN | JSON_PATH) LPAREN! anyArg RPAREN!) |
 			   (TO_RADIX LPAREN! anyArg (COMMA! anyArg)? RPAREN!);

nifi-commons/nifi-expression-language/src/main/java/org/apache/nifi/attribute/expression/language/Query.java

@@ -93,6 +93,7 @@ import org.apache.nifi.attribute.expression.language.evaluation.functions.ToUppe
 import org.apache.nifi.attribute.expression.language.evaluation.functions.TrimEvaluator;
 import org.apache.nifi.attribute.expression.language.evaluation.functions.UrlDecodeEvaluator;
 import org.apache.nifi.attribute.expression.language.evaluation.functions.UrlEncodeEvaluator;
+import org.apache.nifi.attribute.expression.language.evaluation.functions.EscapeJsonEvaluator;
 import org.apache.nifi.attribute.expression.language.evaluation.functions.UuidEvaluator;
 import org.apache.nifi.attribute.expression.language.evaluation.literals.BooleanLiteralEvaluator;
 import org.apache.nifi.attribute.expression.language.evaluation.literals.NumberLiteralEvaluator;
@@ -191,6 +192,7 @@ import static org.apache.nifi.attribute.expression.language.antlr.AttributeExpre
 import static org.apache.nifi.attribute.expression.language.antlr.AttributeExpressionParser.TRUE;
 import static org.apache.nifi.attribute.expression.language.antlr.AttributeExpressionParser.URL_DECODE;
 import static org.apache.nifi.attribute.expression.language.antlr.AttributeExpressionParser.URL_ENCODE;
+import static org.apache.nifi.attribute.expression.language.antlr.AttributeExpressionParser.ESCAPE_JSON;
 import static org.apache.nifi.attribute.expression.language.antlr.AttributeExpressionParser.UUID;
 
 import org.apache.nifi.attribute.expression.language.evaluation.selection.MappingEvaluator;
@@ -922,6 +924,10 @@ public class Query {
                 verifyArgCount(argEvaluators, 0, "urlDecode");
                 return addToken(new UrlDecodeEvaluator(toStringEvaluator(subjectEvaluator)), "urlDecode");
             }
+            case ESCAPE_JSON: {
+                verifyArgCount(argEvaluators, 0, "escapeJson");
+                return addToken(new EscapeJsonEvaluator(toStringEvaluator(subjectEvaluator)), "urlDecode");
+            }
             case SUBSTRING_BEFORE: {
                 verifyArgCount(argEvaluators, 1, "substringBefore");
                 return addToken(new SubstringBeforeEvaluator(toStringEvaluator(subjectEvaluator),

nifi-commons/nifi-expression-language/src/main/java/org/apache/nifi/attribute/expression/language/evaluation/functions/EscapeJsonEvaluator.java

@@ -0,0 +1,47 @@
+/*
+ * 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.nifi.attribute.expression.language.evaluation.functions;
+
+import java.util.Map;
+
+import org.apache.nifi.attribute.expression.language.evaluation.Evaluator;
+import org.apache.nifi.attribute.expression.language.evaluation.QueryResult;
+import org.apache.nifi.attribute.expression.language.evaluation.StringEvaluator;
+import org.apache.nifi.attribute.expression.language.evaluation.StringQueryResult;
+
+import org.apache.commons.lang3.StringEscapeUtils;
+
+public class EscapeJsonEvaluator extends StringEvaluator {
+
+    private final Evaluator<String> subject;
+
+    public EscapeJsonEvaluator(final Evaluator<String> subject) {
+        this.subject = subject;
+    }
+
+    @Override
+    public QueryResult<String> evaluate(final Map<String, String> attributes) {
+        final String subjectValue = subject.evaluate(attributes).getValue();
+        return new StringQueryResult(subjectValue == null ? "" : StringEscapeUtils.escapeJson(subjectValue));
+    }
+
+    @Override
+    public Evaluator<?> getSubjectEvaluator() {
+        return subject;
+    }
+
+}

nifi-commons/nifi-expression-language/src/test/java/org/apache/nifi/attribute/expression/language/TestQuery.java

@@ -1314,6 +1314,14 @@ public class TestQuery {
         verifyEquals("${line:getDelimitedField(2)}", attributes, " 32");
     }
 
+    @Test
+    public void testEscapeJson() {
+        final Map<String, String> attributes = new HashMap<>();
+
+        attributes.put("string", "making air \"QUOTES\".");
+        verifyEquals("${string:escapeJson()}", attributes, "making air \\\"QUOTES\\\".");
+      }
+
     private void verifyEquals(final String expression, final Map<String, String> attributes, final Object expectedResult) {
         Query.validateExpression(expression, false);
         assertEquals(String.valueOf(expectedResult), Query.evaluateExpressions(expression, attributes, null));