feat: Customizing Cloudevents validation (#594)

Add SPI for custom CloudEvent validation.

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

core/src/main/java/io/cloudevents/core/provider/CloudEventValidatorProvider.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright 2018-Present The CloudEvents Authors
+ * <p>
+ * Licensed 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.cloudevents.core.provider;
+
+import io.cloudevents.CloudEvent;
+import io.cloudevents.core.validator.CloudEventValidator;
+
+import java.util.Iterator;
+import java.util.ServiceConfigurationError;
+import java.util.ServiceLoader;
+
+/**
+ * CloudEventValidatorProvider is a singleton class which loads and access CE Validator service providers on behalf of service clients.
+ */
+public class CloudEventValidatorProvider {
+
+    private static final CloudEventValidatorProvider cloudEventValidatorProvider = new CloudEventValidatorProvider();
+
+    private final ServiceLoader<CloudEventValidator> loader;
+
+    private CloudEventValidatorProvider(){
+        loader = ServiceLoader.load(CloudEventValidator.class);
+    }
+
+    public static CloudEventValidatorProvider getInstance() {
+        return cloudEventValidatorProvider;
+    }
+
+    /**
+     * iterates through available Cloudevent validators.
+     * @param cloudEvent
+     */
+    public void validate(CloudEvent cloudEvent){
+        for (final CloudEventValidator validator : loader) {
+            validator.validate(cloudEvent);
+        }
+    }
+}

core/src/main/java/io/cloudevents/core/v03/CloudEventBuilder.java

@@ -16,9 +16,12 @@
  */
 package io.cloudevents.core.v03;
 
+import io.cloudevents.CloudEvent;
 import io.cloudevents.SpecVersion;
 import io.cloudevents.core.CloudEventUtils;
 import io.cloudevents.core.impl.BaseCloudEventBuilder;
+import io.cloudevents.core.provider.CloudEventValidatorProvider;
+import io.cloudevents.core.v1.CloudEventV1;
 import io.cloudevents.rw.CloudEventContextReader;
 import io.cloudevents.rw.CloudEventContextWriter;
 import io.cloudevents.rw.CloudEventRWException;
@@ -122,7 +125,11 @@ public CloudEventV03 build() {
             throw createMissingAttributeException("type");
         }
 
-        return new CloudEventV03(id, source, type, time, schemaurl, datacontenttype, subject, this.data, this.extensions);
+        CloudEventV03 cloudEvent = new CloudEventV03(id, source, type, time, schemaurl, datacontenttype, subject, this.data, this.extensions);
+        final CloudEventValidatorProvider validator = CloudEventValidatorProvider.getInstance();
+        validator.validate(cloudEvent);
+
+        return cloudEvent;
     }
 
     @Override

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

@@ -21,6 +21,8 @@
 import io.cloudevents.SpecVersion;
 import io.cloudevents.core.CloudEventUtils;
 import io.cloudevents.core.impl.BaseCloudEventBuilder;
+import io.cloudevents.core.provider.CloudEventValidatorProvider;
+import io.cloudevents.core.validator.CloudEventValidator;
 import io.cloudevents.rw.CloudEventContextReader;
 import io.cloudevents.rw.CloudEventContextWriter;
 import io.cloudevents.rw.CloudEventRWException;
@@ -119,7 +121,12 @@ 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);
+
+        final CloudEventValidatorProvider validator = CloudEventValidatorProvider.getInstance();
+        validator.validate(cloudEvent);
+
+        return cloudEvent;
     }
 
     @Override

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

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2018-Present The CloudEvents Authors
+ * <p>
+ * Licensed 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.cloudevents.core.validator;
+
+import io.cloudevents.CloudEvent;
+
+/**
+ * @author Vinay Bhat
+ * 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/test/CloudEventCustomValidator.java

@@ -0,0 +1,17 @@
+package io.cloudevents.core.test;
+
+import io.cloudevents.CloudEvent;
+import io.cloudevents.core.validator.CloudEventValidator;
+
+public class CloudEventCustomValidator implements CloudEventValidator {
+
+    @Override
+    public void validate(CloudEvent cloudEvent) {
+        String namespace = null;
+        if ((namespace = (String) cloudEvent.getExtension("namespace")) != null &&
+            !namespace.equals("sales")){
+            throw new IllegalStateException("Expecting sales in namespace extension");
+        }
+    }
+
+}

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

@@ -142,4 +142,16 @@ void testMissingType() {
         ).hasMessageContaining("Attribute 'type' cannot be null");
     }
 
+    @Test
+    void testValidatorProvider(){
+        assertThatCode(() -> CloudEventBuilder
+            .v1()
+            .withId("000")
+            .withSource(URI.create("http://localhost"))
+            .withType(TYPE)
+            .withExtension("namespace", "order")
+            .build()
+        ).hasMessageContaining("Expecting sales in namespace extension");
+    }
+
 }

core/src/test/resources/META-INF/services/io.cloudevents.core.validator.CloudEventValidator

@@ -0,0 +1 @@
+io.cloudevents.core.test.CloudEventCustomValidator