USTDownloadCache

About

The USTDownloadCache is used by the Ubuntu Security Team to improve the runtime of other packages by caching certain JSON files.

Using USTDownloadCache

Example:

import logging
from ust_download_cache import USTDownloadCache

logger = logging.getLogger("")
download_cache = USTDownloadCache(logger)

url = "URL_GOES_HERE"
data = download_cache.get_data_from_url(url)
metadata = download_cache.get_cache_metadata_from_url(url) # used by USTDownloadCache

Extracting zipped files

USTDownloadCache has the ability to download, extract, and cache either bz2 or gz archives. These files are extracted and stored uncompressed so that the data can be accessed as quickly as possible.

Metadata

The USTDownloadCache relies on metadata contained within the file it is downloading/caching. The JSON must supply a "metadata" key, which provides a timestamp (seconds since the Unix epoch) and time to live (ttl) in seconds. The cached version of the file is considered to be expired when timestamp + ttl > now

{
    "metadata": {
        "timestamp": 1591887905,
        "ttl": 3600,
        "version": "1.0"
    },
    "data": {
        "name1": "value1",
        "name2": "value2"
    }
}

Installation

From Source

To install from source, you can clone this repository and install USTDownloadCache:

$> git clone https://github.com/canonical/ust-download-cache
$> pip3 install --user ./ust-download-cache/

As a dependency

As USTDownloadCache is not in PyPI at the moment, you must use the github tarball in your setup.py:

install_requires = [
        "ust-download-cache @ https://github.com/canonical/ust-download-cache/archive/v1.0.1.tar.gz",
]

Development

Installing precommit hooks

To install the precommit hooks, run

pip3 install --user pre-commit
~/.local/bin/pre-commit install

Running the test suite

You can run the automated test suite by running

$> python3 -m pytest

An HTML code coverage report will be generated at ./htmlcov. You can view this with any web browser (e.g. firefox ./htmlcov/index.html).