feat: Customizing Cloudevents validation

Signed-off-by: vbhat6 <vinayas_bhat@intuit.com>

core/src/main/java/io/cloudevents/core/v1/CloudEventBuilder.java

@@ -21,6 +21,7 @@
 import io.cloudevents.SpecVersion;
 import io.cloudevents.core.CloudEventUtils;
 import io.cloudevents.core.impl.BaseCloudEventBuilder;
+import io.cloudevents.core.validator.CloudEventValidator;
 import io.cloudevents.rw.CloudEventContextReader;
 import io.cloudevents.rw.CloudEventContextWriter;
 import io.cloudevents.rw.CloudEventRWException;
@@ -119,7 +120,31 @@ public CloudEvent build() {
             throw createMissingAttributeException(TYPE);
         }
 
-        return new CloudEventV1(id, source, type, datacontenttype, dataschema, subject, time, this.data, this.extensions);
+        CloudEvent cloudEvent = new CloudEventV1(id, source, type, datacontenttype, dataschema, subject, time, this.data, this.extensions);
+
+        String name = null;
+        try{
+            // check if the header.validator.class is set as a system property,
+            if ((name = System.getProperty("header.validator.class")) != null){
+                Class<?> dynamicClass  = Class.forName(name);
+                Object dynamicObject = dynamicClass.newInstance();
+
+                if (dynamicObject instanceof CloudEventValidator) {
+                    // pluggable implementation of validation implementation
+                    CloudEventValidator cloudEventValidator = (CloudEventValidator) dynamicObject;
+
+                    cloudEventValidator.validate(cloudEvent);
+                }
+                else {
+                    throw new IllegalArgumentException("Passed class is not an instance of CloudEventValidator");
+                }
+            }
+        }
+        catch (ClassNotFoundException | InstantiationException | IllegalAccessException e) {
+            throw new IllegalArgumentException("Unable to load the header.validator.class passed as vm argument = " + name + ". Please check the classpath", e);
+        }
+
+        return cloudEvent;
     }
 
     @Override

core/src/main/java/io/cloudevents/core/validator/CloudEventValidator.java

@@ -0,0 +1,16 @@
+package io.cloudevents.core.validator;
+
+import io.cloudevents.CloudEvent;
+
+/**
+ * Interface which defines validation for CloudEvents attributes and extensions.
+ */
+public interface CloudEventValidator {
+
+    /**
+     * Validate the attributes of a CloudEvent.
+     *
+     * @param cloudEvent the CloudEvent to validate
+     */
+    void validate(CloudEvent cloudEvent);
+}

core/src/test/java/io/cloudevents/core/v1/CloudEventBuilderTest.java

@@ -142,4 +142,48 @@ void testMissingType() {
         ).hasMessageContaining("Attribute 'type' cannot be null");
     }
 
+    @Test
+    void testClassNotFoundExceptionForValidator(){
+
+        System.setProperty("header.validator.class", "io.cloudevents.core.v1.CustomCloudEventValidatorTest");
+            assertThatCode(() -> CloudEventBuilder
+            .v1()
+            .withId("000")
+            .withSource(URI.create("http://localhost"))
+            .withType("aaa")
+            .withExtension("astring", 10)
+            .build()
+        ).hasMessageContaining("Unable to load the header.validator.class passed as vm argument");
+    }
+
+    @Test
+    void testClassCastExceptionForValidator(){
+
+        System.setProperty("header.validator.class", "io.cloudevents.core.v1.CustomCloudEventValidator");
+        assertThatCode(() -> CloudEventBuilder
+            .v1()
+            .withId("000")
+            .withSource(URI.create("http://localhost"))
+            .withType("aaa")
+            .withExtension("astring", 10)
+            .build()
+        ).hasMessageContaining("Passed class is not an instance of CloudEventValidator");
+    }
+
+    /**
+     * This test is to check for the mandatory extension 'namespace' as per Organization need
+     */
+    @Test
+    void testMissingNamespaceExtension(){
+
+        System.setProperty("header.validator.class", "io.cloudevents.core.v1.CustomCloudEventValidatorImpl");
+        assertThatCode(() -> CloudEventBuilder
+            .v1()
+            .withId("000")
+            .withSource(URI.create("http://localhost"))
+            .withType("aaa")
+            .build()
+        ).hasMessageContaining("Extension 'namespace' cannot be null");
+    }
+
 }

core/src/test/java/io/cloudevents/core/v1/CustomCloudEventValidator.java

@@ -0,0 +1,11 @@
+package io.cloudevents.core.v1;
+
+/**
+ * Dummy validation class which does not implement CloudEventValidator class.
+ */
+public class CustomCloudEventValidator {
+
+    void validate(){
+
+    }
+}

core/src/test/java/io/cloudevents/core/v1/CustomCloudEventValidatorImpl.java

@@ -0,0 +1,15 @@
+package io.cloudevents.core.v1;
+
+import io.cloudevents.CloudEvent;
+import io.cloudevents.core.validator.CloudEventValidator;
+
+public class CustomCloudEventValidatorImpl implements CloudEventValidator {
+    @Override
+    public void validate(CloudEvent cloudEvent) {
+
+        if (cloudEvent.getExtension("namespace") == null){
+            throw new IllegalStateException("Extension 'namespace' cannot be null");
+        }
+
+    }
+}