Fix bug where v1 HTTP used v2 API if callback had len 1 (#955)

* Fix bug where v1 HTTP used v2 API if callback had len 1

* Changelog

* Formatter

Author: inlined

CHANGELOG.md

@@ -0,0 +1 @@
+- Fix bug where the <data> arg of https onCall functions sometimes deviates from the documented format.

spec/v1/providers/https.spec.ts

@@ -175,6 +175,28 @@ describe('#onCall', () => {
     };
     expect(cf.run(data, context)).to.deep.equal({ data, context });
   });
+
+  // Regression test for firebase-functions#947
+  it('should lock to the v1 API even with function.length == 1', async () => {
+    let gotData: Record<string, any>;
+    const func = https.onCall((data) => {
+      gotData = data;
+    });
+
+    const req = new MockRequest(
+      {
+        data: { foo: 'bar' },
+      },
+      {
+        'content-type': 'application/json',
+      }
+    );
+    req.method = 'POST';
+
+    const response = await runHandler(func, req as any);
+    expect(response.status).to.equal(200);
+    expect(gotData).to.deep.equal({ foo: 'bar' });
+  });
 });
 
 describe('callable CORS', () => {

src/providers/https.ts

@@ -77,7 +77,12 @@ export function _onCallWithOptions(
   handler: (data: any, context: CallableContext) => any | Promise<any>,
   options: DeploymentOptions
 ): HttpsFunction & Runnable<any> {
-  const func: any = onCallHandler({ origin: true, methods: 'POST' }, handler);
+  // onCallHandler sniffs the function length of the passed-in callback
+  // and the user could have only tried to listen to data. Wrap their handler
+  // in another handler to avoid accidentally triggering the v2 API
+  const fixedLen = (data: any, context: CallableContext) =>
+    handler(data, context);
+  const func: any = onCallHandler({ origin: true, methods: 'POST' }, fixedLen);
 
   func.__trigger = {
     labels: {},

src/v2/providers/https.ts

@@ -144,7 +144,11 @@ export function onCall<T = any, Return = any | Promise<any>>(
   }
 
   const origin = 'cors' in opts ? opts.cors : true;
-  const func: any = onCallHandler({ origin, methods: 'POST' }, handler);
+
+  // onCallHandler sniffs the function length to determine which API to present.
+  // fix the length to prevent api versions from being mismatched.
+  const fixedLen = (req: CallableRequest<T>) => handler(req);
+  const func: any = onCallHandler({ origin, methods: 'POST' }, fixedLen);
 
   Object.defineProperty(func, '__trigger', {
     get: () => {