NIFI-14141 Accept Expression Language statement in GenerateFlowFile, …

…File Size property allowing FlowFiles of variable sizes to be generated. Included some examples of EL statements in Additional Details for GenerateFlowFile.

nifi-extension-bundles/nifi-standard-bundle/nifi-standard-processors/src/main/java/org/apache/nifi/processors/standard/GenerateFlowFile.java

@@ -76,7 +76,8 @@ public class GenerateFlowFile extends AbstractProcessor {
             .description("The size of the file that will be used")
             .required(true)
             .defaultValue("0B")
-            .addValidator(StandardValidators.DATA_SIZE_VALIDATOR)
+            .addValidator(StandardValidators.NON_EMPTY_VALIDATOR)
+            .expressionLanguageSupported(ExpressionLanguageScope.ENVIRONMENT)
             .build();
     public static final PropertyDescriptor BATCH_SIZE = new PropertyDescriptor.Builder()
             .name("Batch Size")
@@ -187,11 +188,13 @@ protected Collection<ValidationResult> customValidate(ValidationContext validati
                     + "text and Unique FlowFiles must be false.").build());
         }
 
+        results.add(StandardValidators.DATA_SIZE_VALIDATOR.validate("File Size", validationContext.getProperty(FILE_SIZE).evaluateAttributeExpressions().getValue(), validationContext));
+
         return results;
     }
 
     private byte[] generateData(final ProcessContext context) {
-        final int byteCount = context.getProperty(FILE_SIZE).asDataSize(DataUnit.B).intValue();
+        final int byteCount = context.getProperty(FILE_SIZE).evaluateAttributeExpressions().asDataSize(DataUnit.B).intValue();
 
         final Random random = new Random();
         final byte[] array = new byte[byteCount];

nifi-extension-bundles/nifi-standard-bundle/nifi-standard-processors/src/main/resources/docs/org.apache.nifi.processors.standard.GenerateFlowFile/additionalDetails.md

@@ -0,0 +1,31 @@
+<!--
+  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.
+-->
+
+# GenerateFlowFile
+
+This processor can be configured to generate variable-sized FlowFiles. The `File Size` property accepts both a literal
+value, e.g. "1 KB", and Expression Language statements. In order to create FlowFiles of variable sizes, the Expression
+Language function `random()` can be used. For example, `${random():mod(101)}` will generate values between 0 and 100,
+inclusive.  A data size label, e.g. B, KB, MB, etc., must be  included in the Expression Language statement since the
+`File Size` property holds a data size value. The table below shows some examples.
+
+| File Size Expression Language Statement    | File Sizes Generated (values are inclusive) |
+|--------------------------------------------|---------------------------------------------|
+| ${random():mod(101)}b                      | 0 - 100 bytes                               |
+| ${random():mod(101)}mb                     | 0 - 100 MB                                  |
+| ${random():mod(101):plus(20)} B            | 20 - 120 bytes                              |
+| ${random():mod(71):plus(30):append("KB")}  | 30 - 100 KB                                 |
+
+See the Expression Language Guide for more details on the `random()` function.

nifi-extension-bundles/nifi-standard-bundle/nifi-standard-processors/src/test/java/org/apache/nifi/processors/standard/TestGenerateFlowFile.java

@@ -19,8 +19,13 @@
 import org.apache.nifi.util.MockFlowFile;
 import org.apache.nifi.util.TestRunner;
 import org.apache.nifi.util.TestRunners;
+import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
 /**
  * Unit tests for the GenerateFlowFile processor.
  */
@@ -73,4 +78,30 @@ public void testDynamicPropertiesToAttributes() {
         generatedFlowFile.assertAttributeEquals("mime.type", "application/text");
     }
 
+    @Test
+    public void testExpressionLanguageSupport() {
+        TestRunner runner = TestRunners.newTestRunner(new GenerateFlowFile());
+        runner.setProperty(GenerateFlowFile.FILE_SIZE, "${random():mod(10):plus(1)}B");  // represents a range of 1-10 bytes, inclusive
+        runner.setProperty(GenerateFlowFile.UNIQUE_FLOWFILES, "true");
+        runner.assertValid();
+
+        // Execute multiple times to ensure adequate distribution of file sizes
+        runner.run(1000);
+
+        runner.assertTransferCount(GenerateFlowFile.SUCCESS, 1000);
+        List<MockFlowFile> flowFiles = runner.getFlowFilesForRelationship(GenerateFlowFile.SUCCESS);
+        Map<Long, Integer> fileSizeDistribution = new HashMap<>();
+        flowFiles.forEach(ff -> {
+            long fileSize = ff.getSize();
+            fileSizeDistribution.put(fileSize, fileSizeDistribution.getOrDefault(fileSize, 0) + 1);
+        });
+        long minSize = fileSizeDistribution.keySet().stream().min(Long::compareTo).orElse(-1L);
+        long maxSize = fileSizeDistribution.keySet().stream().max(Long::compareTo).orElse(-1L);
+
+        // Assert all file sizes fall within the range and that there exists more than one unique file size value
+        Assertions.assertTrue(minSize > 0 && minSize < maxSize);
+        Assertions.assertTrue(maxSize <= 10);
+    }
+
+
 }