feat(web): Relax GrpcWebService request body type

[tottoto]

Relaxes GrpcWebService's request body type.

[tobz]

Hmm, if we have to box the request no matter what, what are we gaining with this change?

[tottoto]

The benefit is the CorsGrpcWeb can handle any kind of body types which has the trait bounds.

[tobz]

While the change itself seems fine, I'm still left with the thought: should we avoid all of the constraints that require a service that accepts Request<BoxBody>?

It seems like if we're going to bother to be totally generic over the request body type in GrpcWebService, we should also do so in CorsWebLayer? Maybe there's a very obvious reason why we can't, but looking at tower_http::cors::Cors shows that it's also generic over the request body... so it feels like we should be able to?

[tottoto]

While the change itself seems fine, I'm still left with the thought: should we avoid all of the constraints that require a service that accepts Request?

It seems like if we're going to bother to be totally generic over the request body type in GrpcWebService, we should also do so in CorsWebLayer? Maybe there's a very obvious reason why we can't, but looking at tower_http::cors::Cors shows that it's also generic over the request body... so it feels like we should be able to?

Since CorsWebLayer does not exist, I respond with information about other parts.

I assume your main question is whether we can avoid requiring a BoxBody in the internal service.

I guess so too. When I was working on this, I was also looking into the implementation of tower_http's Cors service to see if it is possible to avoid the BoxBody. However, it would require an internal design change to the implementation, so I opened this partial change which can be easily done for now.