When to use map_into_left_body or map_into_right_body?

[TheCGDF]

I have read EitherBody doc and Middleware example.

But I'm not sure whether I understood it correctly: It seems that I should use map_into_right_body when I need to return early, and I should use map_into_left_body when I need to transfer to next middleware.

However, the code in ErrorHandlers example confused me because it used map_into_left_body() in add_error_header() while map_into_right_body() was used in add_error_body().

I cannot find the reason that why add_error_header() and add_error_body() are different.

Could someone tell me when to use map_into_left_body() or map_into_right_body() or map_into_boxed_body()?

[TheCGDF]

Okay, I misunderstood the example.

type Response = ServiceResponse<EitherBody<B>>;

left body is B and right body is custom body.