Allow custom exception handling in built-in middlewares

[nidib]

What is the feature you are proposing?

Description

Currently, Hono's middlewares, such as csrf, throw HTTPException by default. However, there is no simple way to customize this behavior to throw a specific application-layer exception.

To achieve this, developers need to wrap the middleware with a try-catch block and rethrow a custom exception, as shown below:

const customCsrf: typeof csrf = options => {
    return createMiddleware(async (c, next) => {
        try {
            const middleware = csrf(options);
            await middleware(c, next);
        } catch (e) {
            if (e instanceof HTTPException) {
                throw new CustomException();
            }

            throw e;
        }
    });
}

const app = new Hono();

app.use(customCsrf());

While this works, it introduces unnecessary boilerplate code.

Proposed Change

Add an optional exception property to specify a custom exception class:

const app = new Hono();

app.use(csrf({ exception: CustomException }))

If an exception is provided, the middleware throws that instead of the default HTTPException. The original exception could be preserved in the cause property for debugging purposes.

Benefits

• Reduces boilerplate code.
• Maintains backward compatibility by defaulting to HTTPException.

[EdamAme-x]

I believe you can create your own custom middleware.

app.use(catchError({ exception: CustomException, middleware: csrf() }))

[nidib]

I believe you can create your own custom middleware.

app.use(catchError({ exception: CustomException, middleware: csrf() }))

That is also a good workaround solution!