Re: [PATCH v2 0/3] upload-pack: support a missing-action

>
> `git pack-objects` already supports a `--missing=<missing-action>`
> option, so that it can avoid erroring out if some objects aren't
> available.
>
> It is interesting to have `git upload-pack` support a similar way to
> avoid sending some objects in case they aren't available on the
> server.
>
> For example, in case both the server and the client are using a
> separate promisor remote that contain some objects, it can be better
> if the server doesn't try to send such objects back to the client, but
> instead let the client get those objects separately from the promisor
> remote. (The client needs to have the separate promisor remote
> configured, for that to work.)
>
> This could work better if there was something, like perhaps a
> capability, for the client to tell the server something like:
>
>   "I know how to fetch missing objects from this and that
>   promisor remotes, so if you choose to, you may omit objects
>   that you know are available from these promisor remotes when
>   sending objects to me."
>
> But that capability could be added later as other similar capabilities
> in this area could be very useful. For example in case of a client
> cloning, something like the following is currently needed:
>
>   GIT_NO_LAZY_FETCH=0 git clone
>       -c remote.my_promisor.promisor=true \
>       -c remote.my_promisor.fetch="+refs/heads/*:refs/remotes/my_promisor/*" \
>       -c remote.my_promisor.url=<MY_PROMISOR_URL> \
>       --filter="blob:limit=5k" server
>
> But it would be nice if there was a capability for the client to say
> that it would like the server to give it information about the
> promisor that it could use, so that the user doesn't have to pass all
> the "remote.my_promisor.XXX" config options on the command like. (It
> would then be a bit similar to the bundle-uri feature where all the
> bundle related information comes from the server.)
>
> Another example use of this feature could be a server where some
> objects have been corrupted or deleted. It could still be useful for
> clients who could get those objects from another source, like perhaps
> a different client, to be able to fetch or clone from the server.
>
> The fact that the new `uploadpack.missingAction` configuration
> variable has to be set to a non default value on the server means that
> regular client users cannot hurt themselves with this feature.
>
> As `git rev-list` also supports a `--missing=<missing-action>` option,
> the first 2 patches in this series are about refactoring related code
> from both `git rev-list` and `git pack-objects` into new
> "missing.{c,h}" files. Patch 3/3 then adds a new
> `uploadpack.missingAction` configuration variable.
>
> The changes since v1 are the following:
>
>   - In patch 1/3 the refactored parse_missing_action_value() function
>     doesn't change the fetch_if_missing global variable anymore. The
>     clients of this function change it by themselves instead.
>
>   - In patch 1/3 a minor typo was also fixed.
>
>   - Old patch 2/4 that added a 'int print_ok' argument to
>     parse_missing_action_value() was removed, and now callers deal
>     with only the values they recognise.
>
> Thanks to Junio for his review and for suggesting of the above
> changes.
>
> Christian Couder (3):
>   rev-list: refactor --missing=<missing-action>
>   pack-objects: use the missing action API
>   upload-pack: allow configuring a missing-action
>
>  Documentation/config/uploadpack.txt |   9 ++
>  Makefile                            |   1 +
>  builtin/pack-objects.c              |  48 ++++++-----
>  builtin/rev-list.c                  |  43 ++--------
>  missing.c                           |  36 ++++++++
>  missing.h                           |  19 +++++
>  t/t5706-upload-pack-missing.sh      | 125 ++++++++++++++++++++++++++++
>  upload-pack.c                       |  19 +++++
>  8 files changed, 242 insertions(+), 58 deletions(-)
>  create mode 100644 missing.c
>  create mode 100644 missing.h
>  create mode 100755 t/t5706-upload-pack-missing.sh
>
> --
> 2.45.1.148.g0f5efb064b
>