f1n63r / feedmixer

A micro web service to fetch and mix entries from Atom and RSS feeds (returns Atom, RSS, or JSON)

FeedMixer

FeedMixer is a tiny WSGI (Python3) micro service which takes a list of feed URLs and returns a new feed consisting of the most recent n entries from each given feed.

Status

Changelog

• v2.0.0 The JSON output now conforms to JSON Feed version 1. This breaks any client which depends on the previous ad-hoc JSON format. That legacy format will continue to be maintained in the v1 branch, so any clients which don't want to update to the JSON Feed format should depend on that branch.
• v1.0.0 Stable API. I'm using it in production for small personal "planet"-like feed aggregators.

API

FeedMixer exposes three endpoints:

• /atom
• /rss
• /json

When sent a GET request they return an Atom, an RSS 2.0, or a JSON feed, respectively. The query string of the GET request can contain these fields:

f

A url-encoded URL of a feed (any version of Atom or RSS). To include multiple feeds, simply include multiple f fields.

n

The number of entries to keep from each field (pass 0 to keep all entries, which is the default if no n field is provided).

full

If set, prefer the full entry content; otherwise prefer the shorter entry summary.

Installation

1. Clone this repository: $ git clone https://github.com/cristoper/feedmixer.git
2. $ cd feedmixer
3. Recommended: use pipenv to create a virtualenv and install dependencies: $ pipenv --three sync

The project consists of three modules:

• feedmixer.py - contains the core logic
• feedmixer_api.py - contains the Falcon-based API. Call wsgi_app() to get a WSGI-compliant object to host.
• feedmixer_wsgi.py - contains an actual WSGI application which can be used as-is or as a template to customize.

Run Locally

The feedmixer_wsgi module instantiates the feedmixer WSGI object (with sensible defaults and a rotating logfile) as both api and application (default names used by common WSGI servers). To start the service with gunicorn, for example, clone the repository and in the root directory run:

$ pipenv run pip3 install gunicorn
$ pipenv run gunicorn feedmixer_wsgi

Note that the top-level install directory must be writable by the server running the app, because it creates the logfiles ('fm.log' and 'fm.log.1') and its cache database ('fmcache.db') there.

As an example, assuming an instance of the FeedMixer app is running on the localhost on port 8000, let's fetch the newest entry each from the following Atom and RSS feeds:

• https://americancynic.net/shaarli/?do=atom
• https://hnrss.org/newest

The constructed URL to GET is:

http://localhost:8000/atom?f=https://americancynic.net/shaarli/?do=atom&f=https://hnrss.org/newest&n=1

Entering it into a browser will return an Atom feed with two entries. To GET it from a client programatically, remember to URL-encode the f fields:

$ curl 'localhost:8000/atom?f=https%3A%2F%2Famericancynic.net%2Fshaarli%2F%3Fdo%3Datom&f=https%3A%2F%2Fhnrss.org%2Fnewest&n=1'

HTTPie is a nice command-line http client that makes testing RESTful services more pleasant:

$ pip3 install httpie
$ http localhost:8000/json f==http://hnrss.org/newest f==http://americancynic.net/atom.xml n==1

HTTP/1.1 200 OK
Connection: close
Date: Mon, 24 Sep 2018 04:23:28 GMT
Server: gunicorn/19.9.0
content-length: 1323
content-type: application/json

{
    "description": "json feed created by FeedMixer.",
    "home_page_url": "http://localhost:8000/json?f=http%3A%2F%2Fhnrss.org%2Fnewest&f=http%3A%2F%2Famericancynic.net%2Fatom.xml&n=1",
    "items": [
        {
            "author": {
                "name": "jedwhite"
            },
            "content_html": "<p>Article URL: <a href=\"https://www.gsb.stanford.edu/insights/power-telling\">https://www.gsb.stanford.edu/insights/power-telling</a></p>\n<p>Comments URL: <a href=\"https://news.ycombinator.com/item?id=18054969\">https://news.ycombinator.com/item?id=18054969</a></p>\n<p>Points: 1</p>\n<p># Comments: 0</p>",
            "date_modified": "2018-09-24T04:13:47Z",
            "date_published": "2018-09-24T04:13:47Z",
            "id": "https://news.ycombinator.com/item?id=18054969",
            "title": "The Power of Telling It Like It Is",
            "url": "https://www.gsb.stanford.edu/insights/power-telling"
        },
        {
            "author": {
                "name": "A. Cynic",
                "url": "https://americancynic.net/about/"
            },
            "content_html": "A review of a friend's book and some thoughts on hell.",
            "date_modified": "2018-09-12T15:03:22Z",
            "date_published": "2018-08-29T18:07:24Z",
            "id": "tag:americancynic.net,2018-08-29:/log/2018/8/29/thou_shalt_not_believe/",
            "title": "Book Review: Thou Shalt Not Believe by John Ubhal",
            "url": "https://americancynic.net/log/2018/8/29/thou_shalt_not_believe/"
        }
    ],
    "title": "FeedMixer feed",
    "version": "https://jsonfeed.org/version/1"
}

Deploy

Deploy FeedMixer using any WSGI-compliant server (uswgi, gunicorn, mod_wsgi, ...). Refer to the documentation of the server of your choice.

mod_wsgi

This is how I've deployed FeedMixer with Apache and mod_wsgi (on Debian):

1. Create a directory outside of your Apache DocumentRoot in which to install: $ sudo mkdir /usr/lib/wsgi-bin
2. Install as above (so the cloned repo is at /usr/lib/wsgi-bin/feedmixer)
3. Give Apache write permissions: $ sudo chown :www-data feedmixer; sudo chmod g+w feedmixer
4. Configure Apache using something like the snippet below (either in apache2.conf or in a VirtualHost directive):

WSGIDaemonProcess feedmixer threads=10 \
    python-home=/usr/lib/wsgi-bin/feedmixer/venv \
    python-path=/usr/lib/wsgi-bin/feedmixer \
    home=/usr/lib/wsgi-bin/feedmixer
WSGIProcessGroup feedmixer
WSGIApplicationGroup %{GLOBAL}
WSGIScriptAlias /feedmixer /usr/lib/wsgi-bin/fm/feedmixer_wsgi.py
<Directory "/usr/lib/wsgi-bin/fm">
    Require all granted
    Header set Access-Control-Allow-Origin "*"
</Directory>

The main things to note are the python-home (set to the virtualenv directory), python-path, and home options to the WSGIDaemonProcess.

As configured above, Apache will run the WSGI app in a single process, handling concurrent requests on up to 10 threads. It is also possible to pass the processes=N directive to WSGIDaemonProcess in order to run the app in N processes. If feedmixer_wsgi.py detects that the WSGI server is running it in multiple processes, it will log to syslog instead of to a file.

Also note the CORS header in the Directory directive which allows the feed to be fetched by JavaScript clients from any domain (this requires mod_headers to be enabled). Restrict (or remove) as your application requires.

Docker

An alternative to using a virtualenv for both building and deploying is to run FeedMixer in a Docker container. The included Dockerfile will produce an image which runs FeedMixer using gunicorn.

Build the image from the feedmixer directory:

$ docker build . -t feedmixer

Run it in the foreground:

$ docker run -p 8000:8000 feedmixer

Now from another terminal you should be able to connect to FeedMixer on localhost port 8000 just as in the example above.

Troubleshooting

Using the provided feedmixer_wsgi.py application, information and errors are logged to the file fm.log in the directory the application is started from (auto rotated with a single old log called fm.1.log).

Any errors encountered in fetching and parsing remote feeds are reported in a custom HTTP header called X-fm-errors.

Database Pruning

The included prune_expired.py script can be used to prune old entries from the database (for example by running it from cron):

>>>  /path/to/venv/bin/python3 prune_expired.py 'dbname.db' 1200

The first argument is the path to the ShelfCache database file, and the second argument is the age threshold (in seconds), any entries older than which will be deleted.

Non-features

FeedMixer does not (yet?) do these things itself, though finding or writing suitable WSGI middleware is one way to get them (running it behind a reverse proxy server like nginx is another way):

• Authentication
• Rate limiting

Hacking

First install as per instructions above.

Documentation

Other than this README, the documentation is in the docstrings. To build a pretty version (HTML) using Sphinx:

1. Install Sphinx dependencies: $ pipenv run pip install -r doc/requirements.txt
2. Change to doc/ directory: $ cd doc
3. Build: $ pipenv run make html
4. View: $ x-www-browser _build/html/index.html

Tests

Tests are in the test directory and Python will find and run them with:

$ pipenv run python3 -m unittest

Typechecking

To check types using mypy:

$ MYPYPATH=stub/ mypy --ignore-missing-imports -p feedmixer

Not everything is stubbed out, but can be useful for catching bugs after changing feedparser.py

Get help

Feel free to open an issue on Github for help: https://github.com/cristoper/feedmixer/issues

Support the project

If this package was useful to you, please consider supporting my work on this and other open-source projects by making a small (like a tip) one-time donation: donate via PayPal

If you're looking to contract a Python developer, I might be able to help. Contact me at [email protected]

License

The project is licensed under the WTFPL license, without warranty of any kind.