Adding a simple dataref extension, similar to the java sdk

Signed-off-by: Matthias Wessendorf <mwessend@redhat.com>

v2/extensions/dataref_extension.go

@@ -0,0 +1,36 @@
+/*
+ Copyright 2024 The CloudEvents Authors
+ SPDX-License-Identifier: Apache-2.0
+*/
+
+package extensions
+
+import (
+	"github.com/cloudevents/sdk-go/v2/event"
+	"net/url"
+)
+
+const DataRefExtensionKey = "dataref"
+
+type DataRefExtension struct {
+	DataRef string `json:"dataref"`
+}
+
+func AddDataRefExtension(e *event.Event, dataRef string) error {
+	if _, err := url.Parse(dataRef); err != nil {
+		return err
+	}
+	e.SetExtension(DataRefExtensionKey, dataRef)
+	return nil
+}
+
+func GetDataRefExtension(e event.Event) (DataRefExtension, bool) {
+	if dataRefValue, ok := e.Extensions()[DataRefExtensionKey]; ok {
+		dataRefStr, ok := dataRefValue.(string)
+		if !ok {
+			return DataRefExtension{}, false
+		}
+		return DataRefExtension{DataRef: dataRefStr}, true
+	}
+	return DataRefExtension{}, false
+}

v2/extensions/dataref_extension_test.go

@@ -0,0 +1,41 @@
+/*
+ Copyright 2024 The CloudEvents Authors
+ SPDX-License-Identifier: Apache-2.0
+*/
+
+package extensions
+
+import (
+	"testing"
+
+	"github.com/cloudevents/sdk-go/v2/event"
+)
+
+func TestAddDataRefExtensionValidURL(t *testing.T) {
+	e := event.New()
+	expectedDataRef := "https://example.com/data"
+
+	err := AddDataRefExtension(&e, expectedDataRef)
+	if err != nil {
+		t.Fatalf("Failed to add DataRefExtension with valid URL: %s", err)
+	}
+}
+
+func TestAddDataRefExtensionInvalidURL(t *testing.T) {
+	e := event.New()
+	invalidDataRef := "://invalid-url"
+
+	err := AddDataRefExtension(&e, invalidDataRef)
+	if err == nil {
+		t.Fatal("Expected error when adding DataRefExtension with invalid URL, but got none")
+	}
+}
+
+func TestGetDataRefExtensionNotFound(t *testing.T) {
+	e := event.New()
+
+	_, ok := GetDataRefExtension(e)
+	if ok {
+		t.Fatal("Expected not to find DataRefExtension, but did")
+	}
+}