User Data Download

Users can download a ZIP file with their own submission source code and comments. LCOJ ships with this enabled; this page helps you change the rate limit, turn the feature off, clean up old files, and troubleshoot.

⏱ ~15 min · 👤 Operators · 🔑 SSH + permission to run docker compose on the server

Do you need this?

This feature lets each user download a ZIP file with the source code of their submissions and their comments.

• LCOJ ships with this feature enabled, with nginx and the Docker volume already configured. You don't need to do anything to make it work.
• Read this page if you want to change the rate limit, turn the feature off, clean up old files, or troubleshoot user reports.

Before you start

• You can SSH into the server and run docker compose in the dmoj/ directory.
• The site, celery, and nginx services are running (docker compose ps). ZIP files are built by Celery (the background task queue).
• You know where the config files live: see Environment and configuration.

Status in LCOJ

Component	Value in the shipped config
DMOJ_USER_DATA_DOWNLOAD	True (the default in dmoj/settings.py is False)
DMOJ_USER_DATA_CACHE	'/userdatacache'
DMOJ_USER_DATA_INTERNAL	'/userdatacache'
DMOJ_USER_DATA_DOWNLOAD_RATELIMIT	datetime.timedelta(days=1)
userdatacache volume	Mounted into site, celery, and nginx at /userdatacache/
nginx	Already has location /userdatacache { internal; root /; }

How it works

1. The ZIP file is built by Celery, not by site. That's why celery also needs access to the cache directory.
2. Each user has only one file, named <profile id>.zip. A new request overwrites the previous file.
3. The nginx location is marked internal, so nobody can fetch files directly via /userdatacache/.... Files are only served through /data/download/, which requires login and only returns the requesting user's own file.

Guide for users

1. Sign in and open Edit profile (/edit/profile/).
2. Click the Download your data link. It leads to /data/prepare/.
3. Choose what to download:
   • Download comments?: your comments.
   • Download submissions?: your submissions. You can filter by problem code (a glob such as APLUS*; default *) and by result (AC, WA, ...; leave empty to include everything).
4. Submit the form and wait for the progress page to finish.
5. Click the download button. The file is named <username>-data.zip.

Rate limit

After each request, a user has to wait DMOJ_USER_DATA_DOWNLOAD_RATELIMIT (1 day) before preparing a new file. An already prepared file can be downloaded again at any time. If the file is removed from the cache, the user may prepare a new one immediately.

ZIP contents

<username>-data.zip
├── submissions/
│   ├── info.json          # details for every submission, keyed by id
│   ├── 123456.cpp         # source code, extension depends on the language
│   └── ...
└── comments/
    ├── info.json          # details for every comment, keyed by id
    ├── 789.txt            # comment body
    └── ...

Each entry in submissions/info.json:

{
    "123456": {
        "problem": "APLUSB",
        "date": "2026-01-01T00:00:00+00:00",
        "time": 0.01,
        "memory": 2048.0,
        "language": "CPP17",
        "status": "D",
        "result": "AC",
        "case_points": 100.0,
        "case_total": 100.0
    }
}

Each entry in comments/info.json has date, related_object (problem, contest, blog post, or problem editorial), page, and score.

Changing the configuration

These settings live in dmoj/config/local_settings.py. The site reads the copy at dmoj/repo/dmoj/local_settings.py (copied by ./scripts/initialize). Edit the file in config/ and copy it again, or edit both. local_settings.py does not read these settings from environment variables. See Environment and configuration.

Goal	Change
Allow a new file every 7 days	DMOJ_USER_DATA_DOWNLOAD_RATELIMIT = datetime.timedelta(days=7)
Turn the feature off	DMOJ_USER_DATA_DOWNLOAD = False (the link disappears and /data/... returns 404)

After editing, restart both site and celery (celery builds the files, so it needs the new config too):

cd dmoj
docker compose restart site celery

Don't change the paths unless you have to

/userdatacache must match the volume in docker-compose.yml and the location in nginx.conf. If you change DMOJ_USER_DATA_CACHE or DMOJ_USER_DATA_INTERNAL, update both of those as well, then run docker compose up -d site celery nginx.

Cleaning up old files

LCOJ does not delete ZIP files automatically. Each user has only one file, so storage doesn't grow without bound, but files stay in the volume after users download them. Clean up periodically.

Deletes files

The commands below permanently delete ZIP files in the userdatacache volume. Double-check the /userdatacache/ path and the -name '*.zip' filter before running them.

Run it manually (from the dmoj/ directory):

docker compose exec -T site find /userdatacache/ -type f -name '*.zip' -mtime +2 -delete

Or add a cron job on the host (crontab -e), adjusting the path:

0 */4 * * * cd /path/to/lcoj-docker/dmoj && docker compose exec -T site find /userdatacache/ -type f -name '*.zip' -mtime +2 -delete

• 0 */4 * * *: runs at minute 0, every 4 hours.
• -mtime +2: only deletes files older than about 2 days.

Choosing a retention time

Keep files longer than DMOJ_USER_DATA_DOWNLOAD_RATELIMIT. Since users can prepare a new file as soon as theirs is deleted, deleting too early defeats the rate limit.

Verify

1. Sign in with a regular account and open /edit/profile/: the Download your data link is shown (if the feature is on).
2. Open /data/prepare/, choose your data, and submit the form. The progress page runs until it completes.
3. Click download: you get <username>-data.zip containing submissions/ and/or comments/.
4. Open /data/prepare/ again right away: the page shows how long you must wait before preparing a new file, meaning the rate limit works.
5. If you turned the feature off: the link is gone and /data/prepare/ returns 404.

Troubleshooting

Symptom	Cause	Fix
No "Download your data" link	Feature disabled, or the account is muted (muted users get 404)	Check DMOJ_USER_DATA_DOWNLOAD and the mute status
Progress page never finishes	Celery isn't running	docker compose ps celery, docker compose logs -f celery
Task fails with No such file or directory	Celery can't see /userdatacache	Make sure the userdatacache volume is mounted into celery
/data/download/ returns 404	The file hasn't been prepared or was cleaned up	Prepare it again from /data/prepare/
Download is empty or nginx returns 404	nginx can't see the file	Make sure the volume is mounted into nginx and the /userdatacache location exists in nginx.conf
User is told to wait	DMOJ_USER_DATA_DOWNLOAD_RATELIMIT hasn't elapsed	Wait, or download the previously prepared file

Next steps

• Day-to-day operations: logs, restarting services, and other routine maintenance.
• Environment and configuration: other settings in local_settings.py.
• Contest data download: the similar feature for contest organizers.

Need help?

Open an issue at github.com/luyencode/lcoj-docker/issues, find more at behitek.com, or contact us via luyencode.net/about/#lien-he.