Fix top level return incompatibility (#818)

* Run transformation functions at top level

* changelog

changelog.d/818.bugfix

@@ -0,0 +1 @@
+Fix transformation scripts breaking if they include a `return` at the top level

src/Connections/GenericHook.ts

@@ -332,7 +332,7 @@ export class GenericHookConnection extends BaseConnection implements IConnection
         ctx.runtime.setInterruptHandler(shouldInterruptAfterDeadline(Date.now() + TRANSFORMATION_TIMEOUT_MS));
         try {
             ctx.setProp(ctx.global, 'HookshotApiVersion', ctx.newString('v2'));
-            const ctxResult = ctx.evalCode(`const data = ${JSON.stringify(data)};\n\n${this.state.transformationFunction}`);
+            const ctxResult = ctx.evalCode(`const data = ${JSON.stringify(data)};\n(() => { ${this.state.transformationFunction} })();`);
 
             if (ctxResult.error) {
                 const e = Error(`Transformation failed to run: ${JSON.stringify(ctx.dump(ctxResult.error))}`);

tests/connections/GenericHookTest.ts

@@ -11,6 +11,7 @@ const ROOM_ID = "!foo:bar";
 
 const V1TFFunction = "result = `The answer to '${data.question}' is ${data.answer}`;";
 const V2TFFunction = "result = {plain: `The answer to '${data.question}' is ${data.answer}`, version: 'v2'}";
+const V2TFFunctionWithReturn = "result = {plain: `The answer to '${data.question}' is ${data.answer}`, version: 'v2'}; return;";
 
 async function testSimpleWebhook(connection: GenericHookConnection, mq: LocalMQ, testValue: string) {
     const webhookData = {simple: testValue};
@@ -199,6 +200,29 @@ describe("GenericHookConnection", () => {
             type: 'm.room.message',
         });
     });
+    it("will handle a hook event with a top-level return", async () => {
+        const webhookData = {question: 'What is the meaning of life?', answer: 42};
+        const [connection, mq] = createGenericHook({name: 'test', transformationFunction: V2TFFunctionWithReturn}, {
+                enabled: true,
+                urlPrefix: "https://example.com/webhookurl",
+                allowJsTransformationFunctions: true,
+            }
+        );
+        const messagePromise = handleMessage(mq);
+        await connection.onGenericHook(webhookData);
+        expect(await messagePromise).to.deep.equal({
+            roomId: ROOM_ID,
+            sender: connection.getUserId(),
+            content: {
+                body: "The answer to 'What is the meaning of life?' is 42",
+                format: "org.matrix.custom.html",
+                formatted_body: "<p>The answer to 'What is the meaning of life?' is 42</p>",
+                msgtype: "m.notice",
+                "uk.half-shot.hookshot.webhook_data": webhookData,
+            },
+            type: 'm.room.message',
+        });
+    });
     it("will fail to handle a webhook with an invalid script", async () => {
         const webhookData = {question: 'What is the meaning of life?', answer: 42};
         const [connection, mq] = createGenericHook({name: 'test', transformationFunction: "bibble bobble"}, {