setuptools 60.0 switched from standard library distutils to its own
local distutils by default [1]. setuptools' own distutils version
doesn't support building with 2to3 translation anymore [2].

However, the current pycryptodomex version (3.6) relies on distutils
2to3 translation support for correct Python 3 builds. Building with the
setuptools distutils version results in run-time errors such as

  . . .
    File "/opt/hostedtoolcache/Python/3.8.12/x64/lib/python3.8/site-packages/cms-1.5.dev0-py3.8.egg/cmscommon/crypto.py", line 31, in <module>
      from Cryptodome.Cipher import AES
    File "/opt/hostedtoolcache/Python/3.8.12/x64/lib/python3.8/site-packages/Cryptodome/Cipher/__init__.py", line 31, in <module>
      from Cryptodome.Cipher._mode_ctr import _create_ctr_cipher
    File "/opt/hostedtoolcache/Python/3.8.12/x64/lib/python3.8/site-packages/Cryptodome/Cipher/_mode_ctr.py", line 37, in <module>
      from Cryptodome.Util.number import long_to_bytes
    File "/opt/hostedtoolcache/Python/3.8.12/x64/lib/python3.8/site-packages/Cryptodome/Util/number.py", line 399
      s = pack('>I', n & 0xffffffffL) + s
                                   ^
  SyntaxError: invalid syntax

We set the SETUPTOOLS_USE_DISTUTILS environment variable to continue
using the system distutils version with 2to3 translation support for
now. The variable can be removed later when we update to a newer
pycryptodomex version.

In the documentation, we also pass the environment variable to the
"setup.py install" command for consistency.

[1] pypa/setuptools@f7a55da
[2] pypa/setuptools@d989cdb

* Update user interface to support joining to contests

There are 2 tabs, one for creating new user and one for register
with an existing account. Note that the register page sould be
scrollable because of the long form inside it. So it can not use
login_box class.

* Implement logic of join contest without user creation

* Add contributor's name and copyright

* Check participations only when joining a contest

* Disable and hide register fields when joining to contest

The previous method had 2 different forms but the new method has a single
form and just disables extra fields if they're unused

* Clear field errors after each tab switch

* Small updates

Co-authored-by: Andrey Vihrov <andrey.vihrov@gmail.com>

* Ignore wrong contest submissions in ProxyService

When you are running cms with more than a contest (ie multicontest)
ProxyService can be notified by ScoringService of new submissions of any
contest, ignoring the `-c X` flag of PS. This will lead to `Inconsistent Data`
errors in RWS due to submissions of the wrong contest (bad user, bad
task, ...). This is especially bad because the wrong submission can be sent
with other valid submissions, and RWS drop them all.

The proposed fix just ignores those submissions from ProxyService since
ScoringService has no way to know which contest PS is bound to.

* Move the contest_id checks in submission_scored/tokened

* Move PS contest checks before submission validation

Filter out the submissions from the wrong contest before rejecting them
if they are hidden/unofficial. Add also some debug logging when it
happens.

This also adds the check in dataset_updated() since AWS may trigger the
same kind of wrong RWS notifications.

* Fix line lengths and message format

* Fix support for services connected via IPv6

Use the correct address family when connecting to the various RPC services.

The solution is basically the same suggested here:
#157 (comment)

This work is the result of the work of @edomora97, @mark03 and @dariost.

* Mock getaddrinfo in test_background_connect

Calling getaddrinfo somehow breaks the mocking interface of socket,
replacing the MagicMock with the original function. This would break the
assert and the test in general.
To prevent so getaddrinfo is mocked as well, making it return just an
address without side effects.

* Try all the resolved addresses

- Try to resolve only with the SOCK_STREAM type
- Try to connect to all the resolved IP addresses, sometimes the first
  in the list is not the correct one (e.g. IPv4/v6)
- Remove redundant getaddrinfo in _connection_handler

* Stop after the first connection

* Pass family, type and proto to socket.socket()

As suggested in https://docs.python.org/3/library/socket.html#socket.getaddrinfo

* Fix tests

The import may sometimes fail if the keyserver is unavailable. We try
multiple keyservers in order until the import succeeds.

Fixes: c9d7e02

* Fix CI

* Use apt-get instead of apt

> WARNING: apt does not have a stable CLI interface. Use with caution in scripts.

Ubuntu 20.04 with Python 3.8 has been supported for a while. Meanwhile,
Python 3.6 was released about five years ago, and is nearing the end of
official support.

Codecov recently introduced a new Node-based uploader to replace the
old Bash uploader [1]. The old Bash uploader is deprecated and will be
removed later.

The new uploader's integrity is checked according to Codecov
recommendations. This was highlighted after a recent Codecov security
breach [2].

The new uploader is significantly larger, so it is cached between runs.

See also: GitHub Codecov action [3].

[1] https://about.codecov.io/blog/introducing-codecovs-new-uploader/
[2] https://about.codecov.io/security-update/
[3] https://github.com/marketplace/actions/codecov

* feat: Allow DumpExporter to only export tasks

* fix: Dump exporter tests

* fix: Add DumpExporterTest for skip_users, fix bug

* feat: Add no-users option to DumpImporter

* fixup

Co-authored-by: Andrey Vihrov <andrey.vihrov@gmail.com>

* BugFix: Italian contest exporter and communication tasks

When the task is a communication task and it has no stubs,
exporter assumes "alone" and "std_io".
It only changes its mind to "stub" and "fifo_io" when a stub of
any language is found.

* Yaml format extended with user_io option

This option overrides the default asumption of User I/O option in
communication tasks (stdin/stdout in tasks without stubs and
fifos in tasks with stubs).

* Formatting (maximum line length)

…1193)

* BugFix: Italian contest loader is able to load contest without participants

* Unnecesary semicolon removed

Co-authored-by: Andrey Vihrov <andrey.vihrov@gmail.com>

Suggested-by: @romagnolimarco

* Update Czech translation

* Fix Last-Translator field in Czech translation

* Fix forgotten translation and change different translation

Use hash  instead if ip_hash because the latter only considers the first three octets of the IP address, and in usual settings those octects have a low variability

This covers the following GitHub security advisories:
- GHSA-gxr4-xjj5-5px2
- GHSA-jpcq-cgw6-v4j6
- CVE-2019-11358
- CVE-2015-9251

The jQuery Migrate library is also added to maintain compatibility
with the current Bootstrap version (2.0.4). Without the compatibility
library, the following error occurs when dismissing an alert:

  Uncaught Error: Syntax error, unrecognized expression: #
      jQuery (7)
      close http://localhost:8888/static/js/bootstrap.js:7
      jQuery (8)
      <anonymous> http://localhost:8888/static/js/bootstrap.js:7
      jQuery (13)
  jquery-3.6.0.min.js:2:13639

Language executable file names can now have extensions. This allows to
simplify language compilation commands in multiple cases.

Task type plugins and tests are updated accordingly.

Ensure that no two workers on the same machine simultaneously
try to precache files. All workers except one skip precaching.

This has several effects:
 - Workers precache files for the selected contest.
 - ES only looks for missing operations for the selected contest.
 - invalidate_submission() only invalidates submissions for the selected
   contest if no contest_id, submission_id, dataset_id, participation_id,
   or task_id passed to it.

* Let all services share the file cache directory

* Disallow destroying/purging a shared cache

* After downloading a file, open the temporary file before moving

Even if someone keeps deleting all cached files, a file can always
be used after downloading it just once. (Previously, this could have
become an infinite loop if the file gets deleted sufficiently quickly
every time.)

* Small changes

Edit help message of the `--contest-id` argument

It can happen that the CMS user's primary group name doesn't match the
user name (in case of a pre-existing user), so we should use the actual
group name for setting file permissions.

We don't try to always create and use a "cmsuser" group instead, because
this wouldn't work within a single CI session.