From a73bde1fe8546298644c4ce9de52927fee1e4f98 Mon Sep 17 00:00:00 2001
From: Daniel Castro <dacastr@microsoft.com>
Date: Tue, 13 Feb 2024 15:44:51 -0800
Subject: [PATCH] Update ensureErrorType

---
 src/errors.ts       | 14 ++++++++++++++
 test/errors.test.ts | 19 +++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/src/errors.ts b/src/errors.ts
index 78e3642..b2db275 100644
--- a/src/errors.ts
+++ b/src/errors.ts
@@ -29,6 +29,20 @@ export class ReadOnlyError extends AzFuncTypeError {
 
 export function ensureErrorType(err: unknown): Error & Partial<AzFuncError> {
     if (err instanceof Error) {
+        const writable = Object.getOwnPropertyDescriptor(err, 'message')?.writable;
+        if (!writable) {
+            // The motivation for this branch can be found in the below issue:
+            // https://github.com/Azure/azure-functions-nodejs-library/issues/205
+            let readableMessage = err.message;
+            Object.defineProperty(err, 'message', {
+                get() {
+                    return readableMessage;
+                },
+                set(val: string) {
+                    readableMessage = val;
+                },
+            });
+        }
         return err;
     } else {
         let message: string;
diff --git a/test/errors.test.ts b/test/errors.test.ts
index 7e13cd1..67dc2f9 100644
--- a/test/errors.test.ts
+++ b/test/errors.test.ts
@@ -42,6 +42,25 @@ describe('ensureErrorType', () => {
         expect(ensureErrorType(actualError)).to.equal(actualError);
     });
 
+    it('readonly error', () => {
+        class ReadOnlyError extends Error {
+            get message(): string {
+                return 'a readonly message';
+            }
+        }
+
+        const actualError = new ReadOnlyError();
+
+        // @ts-expect-error: create a function to test that writing throws an exception
+        expect(() => (actualError.message = 'exception')).to.throw();
+
+        const wrappedError = ensureErrorType(actualError);
+        wrappedError.message = 'Readonly error has been modified';
+
+        expect(wrappedError.message).to.equal('Readonly error has been modified');
+        expect(wrappedError.stack).to.contain('Readonly error has been modified');
+    });
+
     function validateError(actual: Error, expectedMessage: string): void {
         expect(actual).to.be.instanceof(Error);
         expect(actual.message).to.equal(expectedMessage);