Contest Data Download

Download a ZIP file with the source code of contestants' submissions after a contest ends.

⏱ ~5 min · 👤 Contest organisers, operators · 🔑 judge.edit_own_contest (author/curator) or judge.edit_all_contest

After a contest ends, its organizers can download the source code of contestants' submissions as a ZIP file, for example to archive it, re-judge it offline or check for cheating.

Before you start

• You are signed in with an account that can edit the contest (see the table below).
• The contest has ended.
• An operator has enabled the feature (see Configuration).

Who can use it?

You must be logged in and able to edit the contest, meaning one of:

Case	Requirement
Contest author or curator	Has the judge.edit_own_contest permission
Administrator	Has the judge.edit_all_contest permission

See also Permissions.

In addition:

• The contest must have ended. Before that, the page says "Please wait until the contest has ended to download data."
• The feature must be enabled (DMOJ_CONTEST_DATA_DOWNLOAD = True). When it is off, the URLs below return 404.

How to download

1. Open the contest page. Users who can edit the contest see a Download data button on it.
2. The Download contest data page (/contest/<contest key>/data/prepare/) has these options:
   • Download submissions? (checked by default): must be checked.
   • Filter by problem code glob: a glob on problem codes, * (everything) by default. For example, LC* only includes problems whose code starts with LC.
   • Filter by result: result codes (AC, WA…). Leave empty to include all submissions.
3. Click Prepare download. You are taken to a progress page while Celery builds the archive.
4. When it is done, click Download prepared data (/contest/<contest key>/data/download/). The file is named <contest key>-data.zip.

Result filter

Using Filter by result can currently make the task fail. If the task fails, leave the result filter empty.

Verify

• The downloaded <contest key>-data.zip opens and has one folder per official participant (see What's in the ZIP).
• If someone is missing: virtual participants and spectators are not included.

Rate limit

Each contest (not each user) can prepare new data once per DMOJ_CONTEST_DATA_DOWNLOAD_RATELIMIT (1 day by default). You can prepare again sooner if the previous ZIP file is no longer on disk. You cannot start a new task while one is still running.

While you wait, the page still lets you download the previously prepared file.

What's in the ZIP

The archive only contains the source code of submissions from official participants (no virtual participants or spectators). There is no CSV, scoreboard or score data.

<contest key>-data.zip
├── alice/
│   ├── APLUSB.cpp               ← alice's highest-scoring submission for APLUSB
│   ├── SORTING.py
│   └── $History/
│       ├── APLUSB_123457.cpp    ← other submissions: <problem code>_<submission ID>.<ext>
│       └── APLUSB_123460.py
└── bob/
    └── APLUSB.java

Rule	Details
Top-level folder	The contestant's username
<problem code>.<ext>	The highest-scoring submission for that problem (ties go to the lowest submission ID)
$History/<problem code>_<ID>.<ext>	Every other submission for that problem
File extension	The extension of the chosen language (e.g. cpp, py, java)
File-upload languages	For languages that submit a file, LCOJ puts the original uploaded file in the ZIP

Configuration (for operators)

The settings live in the site's dmoj/local_settings.py (with Docker, dmoj/repo/dmoj/local_settings.py, copied from dmoj/config/local_settings.py by ./scripts/initialize). They are not read from environment variables, so putting them in environment/site.env has no effect.

Setting	Default in settings.py	Value in LCOJ's Docker config	Meaning
DMOJ_CONTEST_DATA_DOWNLOAD	False	True	Turns the feature on or off
DMOJ_CONTEST_DATA_CACHE	''	'/contestdatacache'	Directory for the ZIP files, one <contest ID>.zip per contest
DMOJ_CONTEST_DATA_INTERNAL	''	'/contestdatacache'	nginx internal path used for X-Accel-Redirect
DMOJ_CONTEST_DATA_DOWNLOAD_RATELIMIT	timedelta(days=1)	timedelta(days=1)	Minimum time between two preparations for the same contest

# dmoj/local_settings.py
DMOJ_CONTEST_DATA_DOWNLOAD = True
DMOJ_CONTEST_DATA_CACHE = '/contestdatacache'
DMOJ_CONTEST_DATA_INTERNAL = '/contestdatacache'
DMOJ_CONTEST_DATA_DOWNLOAD_RATELIMIT = datetime.timedelta(days=1)

In docker-compose.yml, the contestdatacache volume is mounted at /contestdatacache/ in all three of site, celery (which writes the file) and nginx (which serves it). nginx already has an internal location:

location /contestdatacache {
    internal;
    root /;
}

When the site runs behind nginx, Django only returns an X-Accel-Redirect header and nginx sends the file directly. Otherwise, Django reads and returns the file itself.

After editing local_settings.py, restart site and celery (run from dmoj/):

docker compose restart site celery

Cleaning up old files

Each contest has only one ZIP file (a new preparation overwrites the old one), but LCOJ does not delete these files. You can periodically remove files older than 2 days:

WARNING

This command permanently deletes prepared ZIP files. Organizers will have to prepare them again if needed.

# Run from dmoj/
docker compose exec site find /contestdatacache/ -type f -mtime +2 -delete

Example cron entry that runs every 4 hours:

0 */4 * * * docker compose -f /path/to/lcoj-docker/dmoj/docker-compose.yml exec -T site find /contestdatacache/ -type f -mtime +2 -delete

Troubleshooting

Symptom	Cause / fix
No Download data button	The feature is off, or you cannot edit the contest.
403 page saying to wait until the contest ends	The contest has not ended yet.
Progress bar does not move	Check docker compose ps celery and docker compose logs -f celery.
Task fails right after starting	Try leaving Filter by result empty (see the warning above); check write permissions on the cache directory.
Download returns 404	The ZIP has not been built yet or was cleaned up; prepare it again.

Security and privacy

• The ZIP contains contestants' source code. Do not share it publicly without their consent.
• The file can only be downloaded through the Django URL (which checks permissions); the nginx location is internal, so it cannot be accessed directly.
• Users download their own personal data with a separate feature, see User Data Download.

Next steps

• Contest setup: the other contest settings.
• Contest formats: how scoring and ranking work.
• User data download: the personal data download feature.