[ Sent upstream: https://gitlab.com/gitlab-org/gitlab-workhorse/merge_requests/17

  This patch was sent upstream but was not accepted for "complexity"
  reason of auth cache, despite that provides more than an order of magnitude
  speedup. Just carry it with us as NXD ]

In previous patch we added code to serve blob content via running `git cat-file
...` directly, but for every such request a request to slow RoR-based auth
backend is made, which is bad for performance.

Let's cache auth backend reply for small period of time, e.g. 30 seconds, which
will change the situation dramatically:

If we have a lot of requests to the same repository, we query auth backend only
for every Nth request and with e.g. 100 raw blob request/s N=3000 which means
that previous load to RoR code essentially goes away.

On the other hand as we query auth backend only once in a while and refresh the
cache, we will not miss potential changes in project settings. I mean potential
e.g. 25 seconds delay for a project to become public, or vise versa to become
private does no real harm.

The cache is done with the idea to allow the read side codepath to execute in
parallel and to be not blocked by eventual cache updates.

Overall this improves performance a lot:

  (on a 8-CPU i7-3770S with 16GB of RAM, 2001:67c:1254:e:8b::c776 is on localhost)

  # request is handled by gitlab-workhorse, but without auth caching
  $ ./wrk -c40 -d10 -t1 --latency http://[2001:67c:1254:e:8b::c776]:7777/nexedi/slapos/raw/master/software/wendelin/software.cfg
  Running 10s test @ http://[2001:67c:1254:e:8b::c776]:7777/nexedi/slapos/raw/master/software/wendelin/software.cfg
    1 threads and 40 connections
    Thread Stats   Avg      Stdev     Max   +/- Stdev
      Latency   458.42ms   66.26ms 766.12ms   84.76%
      Req/Sec    85.38     16.59   120.00     82.00%
    Latency Distribution
       50%  459.26ms
       75%  490.09ms
       90%  523.95ms
       99%  611.33ms
    853 requests in 10.01s, 1.51MB read
  Requests/sec:     85.18
  Transfer/sec:    154.90KB

  # request goes to gitlab-workhorse with auth caching (this patch)
  $ ./wrk -c40 -d10 -t1 --latency http://[2001:67c:1254:e:8b::c776]:7777/nexedi/slapos/raw/master/software/wendelin/software.cfg
  Running 10s test @ http://[2001:67c:1254:e:8b::c776]:7777/nexedi/slapos/raw/master/software/wendelin/software.cfg
    1 threads and 40 connections
    Thread Stats   Avg      Stdev     Max   +/- Stdev
      Latency    34.52ms   19.28ms 288.63ms   74.74%
      Req/Sec     1.20k   127.21     1.39k    85.00%
    Latency Distribution
       50%   32.67ms
       75%   42.73ms
       90%   56.26ms
       99%   99.86ms
    11961 requests in 10.01s, 21.24MB read
  Requests/sec:   1194.51
  Transfer/sec:      2.12MB

i.e. it is ~ 14x improvement.

[ Sent upstream: https://gitlab.com/gitlab-org/gitlab-workhorse/merge_requests/17

  This patch was sent upstream but was not accepted for "complexity"
  reason of auth cache (next patch), despite that provides more than an
  order of magnitude speedup. Just carry it with us as NXD ]

Currently GitLab serves requests to get raw blobs via Ruby-on-Rails code and
Unicorn. Because RoR/Unicorn is relatively heavyweight, in environment where
there are a lot of simultaneous requests to get raw blobs, this works very slow
and server is constantly overloaded.

On the other hand, to get raw blob content, we do not need anything from RoR
framework - we only need to have access to project git repository on filesystem,
and knowing whether access for getting data from there should be granted or
not. That means it is possible to handle '.../raw/....' request directly
in more lightweight and performant gitlab-workhorse.

As gitlab-workhorse is written in Go, and Go has good concurrency/parallelism
support and is generally much faster than Ruby, moving raw blob serving task to
it makes sense and should be a net win.

In this patch: we add infrastructure to process GET request for '/raw/...':

- extract project / ref and path from URL
- query auth backend for whether download access should be granted or not
- emit blob content via spawning external `git cat-file`

I've tried to mimic the output to be as close as the one emitted by RoR code,
with the idea that for users the change should be transparent.

As in this patch we do auth backend query for every request to get a blob, RoR
code is still loaded very much, so essentially there is no speedup yet:

  (on a 8-CPU i7-3770S with 16GB of RAM, 2001:67c:1254:e:8b::c776 is on localhost)

  # without patch: request eventually goes to unicorn  (9 unicorn workers)
  $ ./wrk -c40 -d10 -t1 --latency http://[2001:67c:1254:e:8b::c776]:7777/nexedi/slapos/raw/master/software/wendelin/software.cfg
  Running 10s test @ http://[2001:67c:1254:e:8b::c776]:7777/nexedi/slapos/raw/master/software/wendelin/software.cfg
    1 threads and 40 connections
    Thread Stats   Avg      Stdev     Max   +/- Stdev
      Latency   461.16ms   63.44ms 809.80ms   84.18%
      Req/Sec    84.84     17.02   131.00     80.00%
    Latency Distribution
       50%  460.21ms
       75%  492.83ms
       90%  524.67ms
       99%  636.49ms
    847 requests in 10.01s, 1.57MB read
  Requests/sec:     84.64
  Transfer/sec:    161.10KB

  # with this patch: request handled by gitlab-workhorse
  $ ./wrk -c40 -d10 -t1 --latency http://[2001:67c:1254:e:8b::c776]:7777/nexedi/slapos/raw/master/software/wendelin/software.cfg
  Running 10s test @ http://[2001:67c:1254:e:8b::c776]:7777/nexedi/slapos/raw/master/software/wendelin/software.cfg
    1 threads and 40 connections
    Thread Stats   Avg      Stdev     Max   +/- Stdev
      Latency   458.42ms   66.26ms 766.12ms   84.76%
      Req/Sec    85.38     16.59   120.00     82.00%
    Latency Distribution
       50%  459.26ms
       75%  490.09ms
       90%  523.95ms
       99%  611.33ms
    853 requests in 10.01s, 1.51MB read
  Requests/sec:     85.18
  Transfer/sec:    154.90KB

In the next patch we'll cache requests to auth backend and that will improve
performance dramatically.

NOTE 20160228: there is internal/git/blob.go trying to get raw data via
    gitlab-workhorse, but still asking Unicorn about blob->sha1 mapping
    etc. That work started in

        86aaa133 (Prototype blobs via workhorse, @jacobvosmaer)

    and was inspired by this patch. It goes out of line compared to what
    we can do if we serve all blob data just by gitlab-workhorse (see
    next patch), so we just avoid git/blob.go and put our stuff into
    git/xblob.go and tweak routes, essentially deactivating git/blob.go
    code.

Project.with_builds_enabled.find_by(runners_token: TOKEN) is not working with project created since upgrade to gitlab v11.11.

From gitlab 8.12 there is new CI job permissions model which only accept login
from ci token for running job. Then the access is revoked after the job is finished.
In Nexedi, when have a lot of URLs which rely on gitlab-ci-token and project-runners-token, so
we need to re-allow access else access to all those URL will be refused.

More info are here: https://docs.gitlab.com/ee/user/project/new_ci_build_permissions_model.html#before-gitlab-8-12

We show in small font size the same info that is shown on sign_in page:

    "GitLab Nexedi Edition", "About GitLab" and "About Nexedi"

This is good to have and hereby-introduced about-footer area will be
also used in the next patch for ICP too.

XXX placement of .about-footer to be near bottom is done not very
correctly.

= GitLab Community Edition + Nexedi patches

Include Merge description message in merge by default. User can disable description in merge message by clicking on `Don't include description in commit message`.

Drop the merge title which is "Merge branch SOURCE into TARGET" and only keep the MR title as commit message.

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