fix: defaults properly handled for emitterFor()

Fixes: https://github.com/cloudevents/sdk-javascript/issues/391

Signed-off-by: Lance Ball <lball@redhat.com>

src/transport/emitter.ts

@@ -28,6 +28,7 @@ export interface TransportFunction {
   (message: Message, options?: Options): Promise<unknown>;
 }
 
+const emitterDefaults = { binding: HTTP, mode: Mode.BINARY };
 /**
  * emitterFactory creates and returns an EmitterFunction using the supplied
  * TransportFunction. The returned EmitterFunction will invoke the Binding's
@@ -41,11 +42,11 @@ export interface TransportFunction {
  * @param {Mode} options.mode the encoding mode (Mode.BINARY or Mode.STRUCTURED)
  * @returns {EmitterFunction} an EmitterFunction to send events with
  */
-export function emitterFor(fn: TransportFunction, options = { binding: HTTP, mode: Mode.BINARY }): EmitterFunction {
+export function emitterFor(fn: TransportFunction, options = emitterDefaults): EmitterFunction {
   if (!fn) {
     throw new TypeError("A TransportFunction is required");
   }
-  const { binding, mode } = options;
+  const { binding, mode } = { ...emitterDefaults, ...options };
   return function emit(event: CloudEvent, opts?: Options): Promise<unknown> {
     opts = opts || {};
 

test/integration/emitter_factory_test.ts

@@ -59,6 +59,47 @@ function gotEmitter(message: Message, options?: Options): Promise<unknown> {
   );
 }
 
+describe("emitterFor() defaults", () => {
+  it("Defaults to HTTP binding, binary mode", () => {
+    function transport(message: Message): Promise<unknown> {
+      // A binary message will have the source attribute as a header
+      expect(message.headers[CONSTANTS.CE_HEADERS.TYPE]).to.equal("emitter.test");
+      return Promise.resolve();
+    }
+    const emitter = emitterFor(transport);
+    emitter(
+      new CloudEvent({
+        id: "1234",
+        source: "/emitter/test",
+        type: "emitter.test",
+      }),
+    );
+  });
+
+  it("Supports HTTP binding, structured mode", () => {
+    function transport(message: Message): Promise<unknown> {
+      console.error(message);
+      // A binary message will have the source attribute as a header
+      expect(message.headers["content-type"]).to.equal(CONSTANTS.DEFAULT_CE_CONTENT_TYPE);
+      const body = JSON.parse(message.body as string);
+      /* @ts-ignore */
+      expect(body.id).to.equal("1234");
+      return Promise.resolve();
+    }
+    // Ignore the next line to ensure that HTTP transport is still the default.
+    // Otherwise, tslint would complain that the param did not have `binding: <val>`
+    /* @ts-ignore */
+    const emitter = emitterFor(transport, { mode: Mode.STRUCTURED });
+    emitter(
+      new CloudEvent({
+        id: "1234",
+        source: "/emitter/test",
+        type: "emitter.test",
+      }),
+    );
+  });
+});
+
 describe("HTTP Transport Binding for emitterFactory", () => {
   beforeEach(() => {
     nock(sink)