Implement error and unauthorized

__tests__/__snapshots__/resolvers.test.js.snap

@@ -38,6 +38,18 @@ exports[`dynamodb resolvers something 2`] = `
 ]
 `;
 
+exports[`error handling error 1`] = `
+{
+  "message": "foo",
+}
+`;
+
+exports[`error handling unauthorized 1`] = `
+{
+  "message": "Unauthorized",
+}
+`;
+
 exports[`rds resolvers attributeExists nested or 1`] = `
 {
   "statements": [

__tests__/helpers.js

@@ -27,6 +27,9 @@ const runResolverFunctionOnAWS = async (code, context, functionName) => {
   });
 
   const result = await client.send(command);
+  if (result.error) {
+    return result.error;
+  }
   try {
     return JSON.parse(result.evaluationResult);
   } catch (e) {
@@ -72,7 +75,14 @@ export const checkResolverValid = async (code, context, functionName) => {
     const fn = module[functionName];
 
     transformContextForAppSync(context);
-    result = fn(context);
+    try {
+      result = fn(context);
+    } catch (e) {
+      if (e.name !== "AppSyncUserError") {
+        throw e;
+      }
+      result = {"message": e.message}
+    }
   }
   expect(result).toMatchSnapshot();
 };

__tests__/resolvers.test.js

@@ -1016,3 +1016,23 @@ describe("rds resolvers", () => {
   });
 });
 
+describe("error handling", () => {
+  test("error", async () => {
+    const code = `
+      export function request(ctx) {
+          util.error("foo")
+        }
+      export function response(ctx) {}
+  `;
+    await checkResolverValid(code, {}, "request");
+  })
+  test("unauthorized", async () => {
+    const code = `
+      export function request(ctx) {
+          util.unauthorized()
+        }
+      export function response(ctx) {}
+  `;
+    await checkResolverValid(code, {}, "request");
+  })
+})

index.js

@@ -1,6 +1,16 @@
 import { v4 as uuidv4 } from 'uuid';
 import { toJsonObject } from './rds/index.js'
 
+class AppSyncUserError extends Error {
+  constructor(message, errorType, data, errorInfo) {
+    super(message);
+    this.name = "AppSyncUserError";
+    this.errorType = errorType;
+    this.data = data;
+    this.errorInfo = errorInfo;
+  }
+}
+
 export const dynamodbUtils = {
   toDynamoDB: function(value) {
     if (typeof (value) === "number") {
@@ -121,8 +131,20 @@ export const util = {
     return uuidv4();
   },
   appendError: function(message, errorType, data, errorInfo) {
-    // This will be handled in LocalStack in a side channel by printing to stderr
-    console.error({ message, errorType, data, errorInfo });
+    const error = { message, errorType, data, errorInfo }
+    if( console.appendError ) {
+      // LocalStack is adding `appendError` to console, allowing to push errors to `context.outErrors`
+      console.appendError(error)
+    } else {
+      // To avoid breaking code where `appendError` is not implemented, we instead print to stderr
+      console.error({ message, errorType, data, errorInfo });
+    }
+  },
+  error: function(message, errorType, data, errorInfo) {
+    throw new AppSyncUserError(message, errorType, data, errorInfo)
+  },
+  unauthorized: function() {
+    throw new AppSyncUserError("Unauthorized", "UnauthorizedException")
   },
   time: {
     nowFormatted: function(pattern) {