Re: [PATCH v4 11/12] convert: add filter.<driver>.process option

> On 06 Aug 2016, at 14:14, Jeff King <peff@peff.net> wrote:
> 
> On Sat, Aug 06, 2016 at 01:55:23PM +0200, Lars Schneider wrote:
> 
>>> And I expect it makes the lives of the client
>>> easier to get a code up front, before it starts taking steps to handle
>>> what it _thinks_ is probably a valid response.
>> 
>> I am not sure I can follow you here. Which actor are you referring to when
>> you write "client" -- Git, right? If the response is rejected right away
>> then Git just needs to read a single flush. If the response experiences
>> an error only later, then the filter wouldn't know about the error when
>> it starts sending. Therefore I don't see how an error code up front could
>> make it easier for Git.
> 
> Yes, I mean git (I see it as the "client" side of the connection in that
> it is making requests of the filter, which will then provide responses).
> 
> What I mean is that the git code could look something like:
> 
>  status == send_filter_request();
>  if (status == OK) {
> 	prepare_storage();
> 	read_response_into_storage();
>  } else {
> 	complain();
>  }
> 
> But if there's no status up front, then you probably have:
> 
>  send_filter_request();
>  prepare_storage();
>  status = read_response_into_storage();
>  if (status != OK) {
> 	rollback_storage();
> 	complain();
>  }
> 
> In the first case, we could easily avoid preparing the storage if our
> request wasn't going to be filled, whereas in the second we have to do
> it unconditionally. That's not a big deal if preparing the storage is
> initializing a strbuf. It's more so if you're opening a temporary object
> file to stream into.
> 
> You _do_ still have to deal with rollback in the first one (for the case
> that the stream ends prematurely for whatever reason). So it's really a
> question of where and how often we expect the failures to come, and
> whether it is worth git knowing up front that the request is not going
> to be fulfilled.
> 
> I dunno. It's not _that_ big a deal to code around. I was just surprised
> not to see an up-front status when responding to a request. It seems
> like the normal thing in just about every protocol I've ever used.