Bug: Event handler response validation typing issues

[nateiler]

Expected Behavior

When performing response body validation for a schema where the input doesn't match the output (coerce) a typing error occurs.

Current Behavior

A schema such as z.object({ id: z.coerce.string(), name: z.string() }) would throw a type error because the input doesn't match the output.

Code snippet

These tests are technically successful, however they illustrate the type error:

it('validates a coerced response object successfully', async () => {
    // Prepare
    const responseSchema = z.object({ id: z.coerce.string(), name: z.string() });

    app.get(
      '/users/:id',
      () => {
        return { id: 123, name: 'John' };
      },
      {
        validation: { res: { body: responseSchema } },
      }
    );

    const event = createTestEvent('/users/123', 'GET', {});
    event.pathParameters = { id: '123' };

    // Act
    const result = await app.resolve(event, context);

    // Assess
    expect(result.statusCode).toBe(200);
  });

It would also be great to allow a response object too:

it('validates response object successfully', async () => {
    // Prepare
    const responseSchema = z.object({ id: z.coerce.string(), name: z.string() });

    app.get(
      '/users/:id',
      () => {
        return Response.json({ id: 123, name: 'John' });
      },
      {
        validation: { res: { body: responseSchema } },
      }
    );

    const event = createTestEvent('/users/123', 'GET', {});
    event.pathParameters = { id: '123' };

    // Act
    const result = await app.resolve(event, context);

    // Assess
    expect(result.statusCode).toBe(200);
  });

Steps to Reproduce

Drop those tests in validation.test.ts

Possible Solution

The TypedRouteHandler could be extended to this:

type TypedRouteHandler<
  TEnv extends Env = Env,
  TReq extends ReqSchema = ReqSchema,
  TResBody extends HandlerResponse = HandlerResponse,
  TRes extends ResSchema = ResSchema,
> = (
  reqCtx: TypedRequestContext<TEnv, TReq, TRes>
) =>
  | Promise<TResBody | ExtendedAPIGatewayProxyResult<TResBody> | Response>
  | TResBody
  | ExtendedAPIGatewayProxyResult<TResBody>
  | Response;

Powertools for AWS Lambda (TypeScript) version

latest

AWS Lambda function runtime

24.x

Packaging format used

npm

Execution logs