Re: [PATCH v1 3/3] convert: add filter.<driver>.useProtocol option

> W dniu 2016-07-25 o 00:36, Ramsay Jones pisze:
>> On 24/07/16 18:16, Lars Schneider wrote:
>>> On 23 Jul 2016, at 01:19, Ramsay Jones <ramsay@ramsayjones.plus.com> wrote:
>>>> On 22/07/16 16:49, larsxschneider@gmail.com wrote:
> [...]
>>>>> This patch adds the filter.<driver>.useProtocol option which, if enabled,
>>>>> keeps the external filter process running and processes all blobs with
>>>>> the following protocol over stdin/stdout.
>>>>> 
>>>>> 1. Git starts the filter on first usage and expects a welcome message
>>>>> with protocol version number:
>>>>> 	Git <-- Filter: "git-filter-protocol\n"
>>>>> 	Git <-- Filter: "version 1"
>>>> 
>>>> Hmm, I was a bit surprised to see a 'filter' talk first (but so long as the
>>>> interaction is fully defined, I guess it doesn't matter).
>>> 
>>> It was a conscious decision to have the `filter` talk first. My reasoning was:
>>> 
>>> (1) I want a reliable way to distinguish the existing filter protocol ("single-shot 
>>> invocation") from the new one ("long running"). I don't think there would be a
>>> situation where the existing protocol would talk first. Therefore the users would
>>> not accidentally mix them with a possibly half working, undetermined, outcome.
>> 
>> If an 'single-shot' filter were incorrectly configured, instead of a new one, then
>> the interaction could last a little while - since it would result in deadlock! ;-)
>> 
>> [If Git talks first instead, configuring a 'single-shot' filter _may_ still result
>> in a deadlock - depending on pipe size, etc.]
> 
> Would it be possible to do an equivalent of sending empty file to the filter?
> If it is misconfigured old-style script, it would exit after possibly empty
> output; if not, we would start new-style interaction.

> 
> This should be, if we agree that detecting misconfigured filters is a good
> thing, tested.
> 
>>> 
>>> (2) In the future we could extend the pipe protocol (see $gmane/297994, it's very
>>> interesting). A filter could check Git's version and then pick the most appropriate
>>> filter protocol on startup.