thoughts about vcl cleanup around (be)resp.body and abandon/synth

[Dridi Boukelmoune]

> - rename vcl_backend_error to vcl_backend_synth to be consistent
>   with the client side

I'd rather have both subroutines and distinguish between actual fetch
errors and artificial backend responses.

As a side note, at some point I remember discussing (with at least
phk) carrying the SLT_Error message in a bereq.error readable only
from v_b_e.

> - add status and reason to abandon which get pre-set for the call
>   to vcl_synth
>
>   503 as default

+1, except for the default but I wouldn't mind it.

> - add return(backend_synth(status, reason)) to vcl_backend_fetch
>   as an easy way to return synthetic content at backend request
>   time.

I don't mind namespacing it, but I'd go for just synth.

> More thoughts:
>
> - if we want the (un)set beresp.body, should we maybe have
>
>         set beresp.body = fetch()
>
>   also?

What happens if I set the beresp.body several times with and without fetch()?

I actually need to check what happens today if you synthetic()/set
*resp.body more than once.

>   This would be the default if no other beresp.body action happend
>   in vcl_backend_response

I have trouble being convinced by the behavior, despite me being
previously in favor of being able to set beresp.body in v_b_r. After
two mental context switches it no longer seems like such a good idea
to me.

Cheers