src(message): adds Detector interface to ease detection of events

Fixes: #295

Signed-off-by: Lance Ball <[email protected]>

Author: lance

src/message/http/index.ts

@@ -26,6 +26,17 @@ export function structured(event: CloudEvent): Message {
   };
 }
 
+// implements Detector
+// TODO: this could probably be optimized
+export function isEvent(message: Message): boolean {
+  try {
+    deserialize(message);
+    return true;
+  } catch (err) {
+    return false;
+  }
+}
+
 /**
  * Converts a Message to a CloudEvent
  *

src/message/index.ts

@@ -1,5 +1,5 @@
 import { CloudEvent } from "..";
-import { binary, deserialize, structured } from "./http";
+import { binary, deserialize, structured, isEvent } from "./http";
 import { headersFor } from "./http/headers";
 
 /**
@@ -11,6 +11,7 @@ export interface Binding {
   binary: Serializer;
   structured: Serializer;
   toEvent: Deserializer;
+  isEvent: Detector;
 }
 
 /**
@@ -54,11 +55,20 @@ export interface Deserializer {
   (message: Message): CloudEvent;
 }
 
+/**
+ * Detector is a function interface that detects whether
+ * a message contains a valid CloudEvent
+ */
+export interface Detector {
+  (message: Message): boolean;
+}
+
 // HTTP Message capabilities
 export const HTTP: Binding = {
   binary: binary as Serializer,
   structured: structured as Serializer,
   toEvent: deserialize as Deserializer,
+  isEvent: isEvent as Detector,
 };
 
 // TODO: Deprecated. Remove this for 4.0

test/integration/message_test.ts

@@ -28,6 +28,26 @@ const dataBinary = Uint32Array.from(JSON.stringify(data), (c) => c.codePointAt(0
 const data_base64 = asBase64(dataBinary);
 
 describe("HTTP transport messages", () => {
+  it("can detect CloudEvent Messages", () => {
+    // Create a message that is not an actual event
+    let message: Message = {
+      body: "Hello world!",
+      headers: {
+        "Content-type": "text/plain",
+      },
+    };
+    expect(HTTP.isEvent(message)).to.be.false;
+
+    // Now create a message that is an event
+    message = HTTP.binary(
+      new CloudEvent({
+        source: "/message-test",
+        type: "example",
+      }),
+    );
+    expect(HTTP.isEvent(message)).to.be.true;
+  });
+
   describe("Specification version V1", () => {
     const fixture: CloudEvent = new CloudEvent({
       specversion: Version.V1,