feat: SQSMessageModel validates required fields of message (#1188)

Allows us to remove the non-null assertions, making this model more
type-safe.

This is unlikely to break any existing applications as this model is
intended for _received_ messages, which have all required fields.

Jira: [ENG-2733]

BREAKING CHANGE: `SQSMessageModel` will throw if required fields
(`MessageID`, `ReceiptHandle`, `Body`) are missing from the SQS message.

Author: seb-cr

docs/migration/v2.md

@@ -168,7 +168,7 @@ The `MarketingPreference` model is removed, as this is application-specific and
 
 The `StatusModel` model has been replaced by a simple object type. See the [StatusModel](#statusmodel) section below.
 
-Other models (`ResponseModel`, `SQSMessageModel`) are unaffected except that they no longer inherit from a common `Model` class.
+Other models (`ResponseModel`, `SQSMessageModel`) are largely unaffected except that they no longer inherit from a common `Model` class.
 
 ### `StatusModel`
 
@@ -211,3 +211,7 @@ async function checkStatus(): Promise<ServiceStatus> {
 ```
 
 Note that we can keep `status` unset initially, and TypeScript will complain if you forget to set it before `checkStatus` returns.
+
+### `SQSMessageModel`
+
+The model constructor will now validate that `message` has all fields required of a received SQS message. This should not break existing applications that are using this model correctly, but is included in the 2.0.0 release as a precaution.

src/models/SQSMessageModel.ts

@@ -15,10 +15,24 @@ export default class Message {
   metadata: Record<string, any> = {};
 
   constructor(message: SQS.Message) {
-    // todo: validate rather than assert the type
-    this.messageId = message.MessageId!;
-    this.receiptHandle = message.ReceiptHandle!;
-    this.body = JSON.parse(message.Body!);
+    if (!message.MessageId) {
+      throw new TypeError('Message does not have a MessageId');
+    }
+    if (!message.ReceiptHandle) {
+      throw new TypeError('Message does not have a ReceiptHandle');
+    }
+    if (!message.Body) {
+      throw new TypeError('Message does not have a Body');
+    }
+
+    this.messageId = message.MessageId;
+    this.receiptHandle = message.ReceiptHandle;
+
+    try {
+      this.body = JSON.parse(message.Body);
+    } catch (error) {
+      throw new TypeError('Message body is not valid JSON');
+    }
   }
 
   /**

tests/unit/models/SQSMessageModel.spec.ts

@@ -1,3 +1,5 @@
+import type { SQS } from 'aws-sdk';
+
 import { SQSMessageModel as Message } from '@/src';
 
 describe('unit.models.SQSMessageModel', () => {
@@ -13,6 +15,38 @@ describe('unit.models.SQSMessageModel', () => {
 
   const messageModel = new Message(mockedMessage);
 
+  describe('constructor', () => {
+    it('should throw if message is missing MessageId', () => {
+      const message: SQS.Message = { ...mockedMessage };
+      delete message.MessageId;
+
+      expect(() => new Message(message)).toThrowError(TypeError);
+    });
+
+    it('should throw if message is missing ReceiptHandle', () => {
+      const message: SQS.Message = { ...mockedMessage };
+      delete message.ReceiptHandle;
+
+      expect(() => new Message(message)).toThrowError(TypeError);
+    });
+
+    it('should throw if message is missing Body', () => {
+      const message: SQS.Message = { ...mockedMessage };
+      delete message.Body;
+
+      expect(() => new Message(message)).toThrowError(TypeError);
+    });
+
+    it('should throw if message body is not valid JSON', () => {
+      const message: SQS.Message = {
+        ...mockedMessage,
+        Body: 'This is not JSON!',
+      };
+
+      expect(() => new Message(message)).toThrowError(TypeError);
+    });
+  });
+
   describe('getMessageId', () => {
     it('should return the message ID', () => {
       expect(messageModel.getMessageId()).toEqual(mockedMessage.MessageId);