fix: explicitly check that request.body is a string (#1010)

* fix: reverts conditional change within `getPayload()` that broke compatibility with fastify/middie middleware library

* updates conditional within `getPayload()`

src/middleware/node/get-payload.ts

@@ -12,18 +12,16 @@ import AggregateError from "aggregate-error";
 type IncomingMessage = any;
 
 export function getPayload(request: IncomingMessage): Promise<string> {
-  if ("body" in request) {
-    if (
-      typeof request.body === "object" &&
-      "rawBody" in request &&
-      request.rawBody instanceof Buffer
-    ) {
-      // The body is already an Object and rawBody is a Buffer (e.g. GCF)
-      return Promise.resolve(request.rawBody.toString("utf8"));
-    } else {
-      // The body is a String (e.g. Lambda)
-      return Promise.resolve(request.body);
-    }
+  if (
+    typeof request.body === "object" &&
+    "rawBody" in request &&
+    request.rawBody instanceof Buffer
+  ) {
+    // The body is already an Object and rawBody is a Buffer (e.g. GCF)
+    return Promise.resolve(request.rawBody.toString("utf8"));
+  } else if (typeof request.body === "string") {
+    // The body is a String (e.g. Lambda)
+    return Promise.resolve(request.body);
   }
 
   // We need to load the payload from the request (normal case of Node.js server)

test/integration/get-payload.test.ts

@@ -74,4 +74,19 @@ describe("getPayload", () => {
 
     expect(await promise).toEqual("foo");
   });
+
+  it("resolves with a string if the body key of the request is defined but value is undefined", async () => {
+    const request = new EventEmitter();
+    // @ts-ignore body is not part of EventEmitter, which we are using
+    // to mock the request object
+    request.body = undefined;
+
+    const promise = getPayload(request);
+
+    // we emit data, to ensure that the body attribute is preferred
+    request.emit("data", "bar");
+    request.emit("end");
+
+    expect(await promise).toEqual("bar");
+  });
 });