django-async-downloads 0.2.0

Asynchronous downloads scaffolding for Django projects

Django Async Downloads

Asynchronous downloads scaffolding for Django projects.

• TODO: describe cache mechanism
• TODO: how to customise the front end

Installation

pip install django-async-downloads

Add to your INSTALLED_APPS:

INSTALLED_APPS = [
    ...
    "async_downloads",
]

Add to your project's url_patterns:

path("async_downloads/", include("async_downloads.urls"))

Add the CSS:

<link rel="stylesheet" type="text/css" href="{% static 'css/async_downloads.css' %}" />

Add the JS:

<script src="{% static "js/async_downloads.js" %}" id="async-downloads-script"
    data-url="{% url 'async_downloads:ajax_update' %}"
    data-clear-url="{% url 'async_downloads:ajax_clear_download' %}"></script>

Include the download centre nav-menu:

<ul class="navbar-nav">
    ...
    {% include 'async_downloads/download_centre.html' %}
    ...

Usage

TODO: using the JS

Cache Functions

cache.init_download

Initialise a download by preparing the cache entries. Returns a tuple of keys, the collection key and specific download key. You would typically want to call this within the web process, and pass the download key (and possibly the collection key) into the asynchronous function call so that the status can be updated.

Arguments:

• pk: the unique identifier for a collection of downloads - this will typically be a user PK
• filename: the name of the file being downloaded (does not need to be unique)
• name: (optional) the name to associate with this download - defaults to filename

cache.save_download

The asynchronous process should call this function when the iterable is prepared in order to save the output. The only supported format is CSV currently.

Arguments:

• download_key: the cache key of this particular download
• iterable: an iterable of data rows to be written

cache.update_percentage

The asynchronous process can call this function to calculate and update the completion percentage. (download_key, total, cur, resolution=10): Arguments:

• download_key: the cache key of this particular download
• total: total to compare current progress against
• cur: current progress index
• resolution: resolution of the percentage calculation (make smaller for fewer updates, larger for more precision); default is 10, meaning it will increase in steps of 10%. The value is capped between 1 and 100.

cache.set_percentage

The asynchronous process can call this function to directly set the completion percentage.

Arguments:

• download_key: the cache key of this particular download
• percentage: an number between 0 and 100 (inclusive)

cache.cleanup_collection

There can be a build up of expired download keys in a collection so it can be worth periodically removing them using this function. (Note that the collection cache itself will expire if not touched for ASYNC_DOWNLOADS_TIMEOUT seconds, so it may not be critical to use this.)

Arguments:

• collection_key: the cache key of a collection of downloads

tasks.cleanup_expired_downloads

Delete expired downloads (where the download no longer exists in the cache). This is a clean up operation to prevent downloads that weren't manually deleted from building up, and should be run periodically to avoid bloating the server with files.

This is best setup as a periodic task in your project, which can be done by adding the following to your project's celery.py:

app.conf.beat_schedule = {
    "async_downloads_cleanup": {
        "task": "async_downloads.tasks.cleanup_expired_downloads",
        "schedule": crontab(hour=0, minute=0, day_of_week=1)
    }
}

Configurable Settings

ASYNC_DOWNLOADS_TIMEOUT

Default: 60 * 60 * 24 (1 day)

This is the cache timeout used for cache operations.

ASYNC_DOWNLOADS_DOWNLOAD_TEMPLATE

Default: "async_downloads/downloads.html"

This is the template that will be used by the ajax_update view. You can override it by creating a template in <project>/templates/async_downloads/downloads.html, or else putting the template wherever you choose and changing this setting.

ASYNC_DOWNLOADS_PATH_PREFIX

Default: "downloads"

The parent directory for all downloads in the MEDIA_ROOT directory.

ASYNC_DOWNLOADS_COLLECTION_KEY_FORMAT

Default: "async_downloads/{}"

The collection key keeps track of the cache keys of a grouped collection of downloads. In the unlikely event that this key format clashes with something in your project, you can change it. The expectation is for the string to have a user primary key inserted with str.format, so {} is required to be present.