[RFC PATCH 0/2] upload-pack.c: limit allowed filter choices

[Taylor Blau <me@ttaylorr.com>]

Hi Christian,

Of course, I would be happy to send along our patches. They are included
in the series below, and correspond roughly to what we are running at
GitHub. (For us, there have been a few more clean-ups and additional
patches, but I squashed them into 2/2 below).

The approach is roughly that we have:

  - 'uploadpack.filter.allow' -> specifying the default for unspecified
    filter choices, itself defaulting to true in order to maintain
    backwards compatibility, and

  - 'uploadpack.filter.<filter>.allow' -> specifying whether or not each
    filter kind is allowed or not. (Originally this was given as 'git
    config uploadpack.filter=blob:none.allow true', but this '=' is
    ambiguous to configuration given over '-c', which itself uses an '='
    to separate keys from values.)

I noted in the second patch that there is the unfortunate possibility of
encountering a SIGPIPE when trying to write the ERR sideband back to a
client who requested a non-supported filter. Peff and I have had some
discussion off-list about resurrecting SZEDZER's work which makes room
in the buffer by reading one packet back from the client when the server
encounters a SIGPIPE. It is for this reason that I am marking the series
as 'RFC'.

For reference, our configuration at GitHub looks something like:

  [uploadpack]
    allowAnySHA1InWant = true
    allowFilter = true
  [uploadpack "filter"]
    allow = false
  [uploadpack "filter.blob:limit"]
    allow = true
  [uploadpack "filter.blob:none"]
    allow = true

with a few irrelevant details elided for the purposes of the list :-).

I'd be happy to take in any comments that you or others might have
before dropping the 'RFC' status.

Taylor Blau (2):
  list_objects_filter_options: introduce 'list_object_filter_config_name'
  upload-pack.c: allow banning certain object filter(s)

 Documentation/config/uploadpack.txt | 12 ++++++
 list-objects-filter-options.c       | 25 +++++++++++
 list-objects-filter-options.h       |  6 +++
 t/t5616-partial-clone.sh            | 23 ++++++++++
 upload-pack.c                       | 67 +++++++++++++++++++++++++++++
 5 files changed, 133 insertions(+)

--
2.26.0.rc2.2.g888d9484cf