CloudEventBuilder should fail when providing an invalid extension name

core/src/main/java/io/cloudevents/core/impl/BaseCloudEventBuilder.java

@@ -97,16 +97,25 @@ public SELF withData(String dataContentType, URI dataSchema, CloudEventData data
     }
 
     public SELF withExtension(@Nonnull String key, String value) {
+        if(!isValidExtensionName(key)){
+            throw CloudEventRWException.newInvalidExtensionName(key);
+        }
         this.extensions.put(key, value);
         return self;
     }
 
     public SELF withExtension(@Nonnull String key, Number value) {
+        if(!isValidExtensionName(key)){
+            throw CloudEventRWException.newInvalidExtensionName(key);
+        }
         this.extensions.put(key, value);
         return self;
     }
 
     public SELF withExtension(@Nonnull String key, Boolean value) {
+        if(!isValidExtensionName(key)){
+            throw CloudEventRWException.newInvalidExtensionName(key);
+        }
         this.extensions.put(key, value);
         return self;
     }
@@ -151,4 +160,25 @@ public CloudEvent end() {
     protected static IllegalStateException createMissingAttributeException(String attributeName) {
         return new IllegalStateException("Attribute '" + attributeName + "' cannot be null");
     }
+    /**
+     * Validates the extension name as defined in  CloudEvents spec
+     * See <a href="https://github.com/cloudevents/spec/blob/master/spec.md#attribute-naming-convention">attribute-naming-convention</a>
+     * @param name the extension name
+     * @return true if extension name is valid, false otherwise
+     */
+    private static boolean isValidExtensionName(String name) {
+        if(name.length() > 20){
+            return false;
+        }
+        char[] chars = name.toCharArray();
+        for (char c: chars)
+        if (!isValidChar(c)) {
+            return false;
+        }
+        return true;
+    }
+
+    private static boolean isValidChar(char c) {
+        return (c >= 'a' && c <= 'z') || (c >= '0' && c <= '9');
+    }
 }

core/src/test/java/io/cloudevents/core/impl/BaseCloudEventBuilderTest.java

@@ -4,9 +4,12 @@
 import io.cloudevents.core.builder.CloudEventBuilder;
 import io.cloudevents.core.extensions.DistributedTracingExtension;
 import io.cloudevents.core.test.Data;
+import io.cloudevents.rw.CloudEventRWException;
 import org.junit.jupiter.api.Test;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 public class BaseCloudEventBuilderTest {
 
@@ -45,4 +48,28 @@ public void copyAndRemoveMaterializedExtension() {
             .isEqualTo(have);
     }
 
+    @Test
+    public void testLongExtensionName() {
+        Exception exception = assertThrows(RuntimeException.class, () -> {
+            CloudEvent cloudEvent = CloudEventBuilder.v1(Data.V1_WITH_JSON_DATA_WITH_EXT)
+                .withExtension("thisextensionnameistoolong", "")
+                .build();
+        });
+        String expectedMessage = "Invalid extensions name: thisextensionnameistoolong";
+        String actualMessage = exception.getMessage();
+
+        assertTrue(actualMessage.contains(expectedMessage));
+    }
+    @Test
+    public void testInvalidExtensionName() {
+        Exception exception = assertThrows(RuntimeException.class, () -> {
+            CloudEvent cloudEvent = CloudEventBuilder.v1(Data.V1_WITH_JSON_DATA_WITH_EXT)
+                .withExtension("ExtensionName", "")
+                .build();
+        });
+        String expectedMessage = "Invalid extensions name: ExtensionName";
+        String actualMessage = exception.getMessage();
+
+        assertTrue(actualMessage.contains(expectedMessage));
+    }
 }