Provided by: feed2exec_0.20.0_all 
NAME
feed2exec-plugins - feed2exec plugin documentation
This is a quick overview of the available plugins.
OUTPUT PLUGINS
Archive
feed2exec.plugins.archive.DEFAULT_ARCHIVE_DIR = '/run/user/1000/'
default archive directory
feed2exec.plugins.archive.output(*args, feed=None, item=None, session=None, **kwargs)
The archive plugin saves the feed’s item.link URLs into a directory, specified by
DEFAULT_ARCHIVE_DIR or through the output args value.
Example:
[NASA breaking news]
url = https://www.nasa.gov/rss/dyn/breaking_news.rss
output = archive
args = /srv/archive/nasa/
The above will save the “NASA breaking news” into the /srv/archive/nasa directory.
Do not use interpolation here as the feed’s variable could be used to mount a
directory transversal attack.
Echo
class feed2exec.plugins.echo.output(*args, feed=None, **kwargs)
This plugin outputs, to standard output, the arguments it receives. It can be
useful to test your configuration. It also creates a side effect for the test suite
to determine if the plugin was called.
This plugin does a similar thing when acting as a filter.
feed2exec.plugins.echo.filter
This filter just keeps the feed unmodified. It is just there for testing purposes.
Error
feed2exec.plugins.error.output(*args, **kwargs)
The error plugin is a simple plugin which raises an exception when called. It is
designed for use in the test suite and should generally not be used elsewhere.
Exec
feed2exec.plugins.exec.output(command, *args, feed=None, **kwargs)
The exec plugin is the ultimate security disaster. It simply executes whatever you
feed it without any sort of sanitization. It does avoid to call to the shell and
executes the command directly, however. Feed contents are also somewhat sanitized
by the feedparser module, see the Sanitization documentation for more information
in that regard. That is limited to stripping out hostile HTML tags, however.
You should be careful when sending arbitrary parameters to other programs. Even if
we do not use the shell to execute the program, an hostile feed could still inject
commandline flags to change the program behavior without injecting shell commands
themselves.
For example, if a program can write files with the -o option, a feed could set
their title to -oevil to overwrite the evil file. The only way to workaround that
issue is to carefully craft the commandline so that this cannot happen.
Alternatively, writing a Python plugin is much safer as you can sanitize the
arguments yourself.
Example:
[NASA What's up?]
url = https://www.nasa.gov/rss/dyn/whats_up.rss
output = feed2exec.plugins.exec
args = wget -P /srv/archives/nasa/ {item.link}
The above is the equivalent of the archive plugin: it will save feed item links to
the given directory.
Maildir
class feed2exec.plugins.maildir.output(to_addr=None, feed=None, item=None, lock=None,
*args, **kwargs)
The maildir plugin will save a feed item into a Maildir folder.
The configuration is a little clunky, but it should be safe against hostile feeds.
Parameters
to_addr (str) – the email to use as “to” (defaults to USER@localdomain)
Example:
[NASA breaking news]
url = https://www.nasa.gov/rss/dyn/breaking_news.rss
mailbox = ~/Maildir/
folder = nasa
args = me@example.com
The above will save new feed items from the NASA feed into the ~/Maildir/nasa/
maildir folder, and will set the To field of the email to me@example.com.
Mbox
class feed2exec.plugins.mbox.output(to_addr=None, feed=None, item=None, lock=None, *args,
**kwargs)
The mbox plugin will save a feed item in a Mbox mailbox.
This is mostly for testing purposes, but can of course be used in the unlikely
event where you prefer mbox folders over the feed2exec.plugins.maildir plugin.
Parameters
to_addr (str) – the email to use as “to” (defaults to USER@localdomain)
Todo There is some overlap between the code here and the maildir implementation.
Refactoring may be in order, particularly if we add another mailbox format,
though that is unlikely.
Null
feed2exec.plugins.null.output(*args, **kwargs)
This plugin does nothing. It can be useful in cases where you want to catchup with
imported feeds.
feed2exec.plugins.null.filter(item=None, *args, **kwargs)
The null filter removes all elements from a feed item
Transmission
feed2exec.plugins.transmission.sanitize(text, repl='-')
like utils.slug, but without lowercase and allow custom replacement
>>> sanitize('test')
'test'
>>> sanitize('../../../etc/password')
'etc-password'
>>> sanitize('Foo./.bar', repl='.')
'Foo.bar'
feed2exec.plugins.transmission.output(hostname='localhost', *args, feed=None, item=None,
**kwargs)
the transmission plugin will send feed items to a transmission instance
it assumes the transmission-remote command is already installed and configured to
talk with transmission.
the hostname is passed in the args configuration and defaults to localhost. the
folder parameter is also used to determine where to save the actual torrents files.
note that this will also append a sanitized version of the item title, if a folder
is provided. this is to allow saving series in the same folder.
if the title is unique for each torrent, you may use a filter to set the title to
the right location.
Wayback
feed2exec.plugins.wayback.output(*args, feed=None, item=None, session=None, **kwargs)
This plugin saves the feed items link element to the wayback machine. It will retry
URLs that fail, so it may be necessary to manually catchup feeds if they have
broken link fields.
There are two wayback machine APIs that can be used, the default one archives the
full page while the other one archives only the page URLs.
The mechanism for archiving the full page uses a browser on the server to download
all the resources used by the page including img/CSS/JS/etc:
https://blog.archive.org/2019/10/23/the-wayback-machines-save-page-now-is-new-and-improved/
Unfortunately the SPN2 page is just a HTML form, the response code is always 200
OK, any errors are returned in a HTML page and there are no easily machine-readable
ways to find the errors on the page so we have to parse the HTML and query it using
XPath based heuristics, but if there are errors in a form that is not yet known
then the unknown errors will not be detected properly.
Example:
[NASA IOTD wayback]
url = https://www.nasa.gov/rss/dyn/lg_image_of_the_day.rss
output = feed2exec.plugins.wayback
args = full
The above will save the Image of the day updates to the wayback machine. Since the
page has images and everything is loaded by JS, using the SPN2 API is necessary to
capture the useful information.
Example:
[ikiwiki RecentChanges wayback]
url = https://ikiwiki.info/recentchanges/index.rss
output = feed2exec.plugins.wayback
args = page
The above will save the ikiwiki RecentChanges to the wayback machine. Since the
page is plain text, saving the full page resources is not really necessary, the CSS
does not add information to the page.
FILTER PLUGINS
Droptitle
feed2exec.plugins.droptitle.filter(*args, feed=None, item=None, **kwargs)
the droptitle filter will drop any feed item with a title matching the given args.
Example:
[NASA breaking news]
url = https://www.nasa.gov/rss/dyn/breaking_news.rss
filter = feed2exec.plugins.droptitle
filter_args = Trump
The above will process the feed items according to the global configuration, but
will skip any item that has the word “Trump” anywhere in the title field.
Arguments are processed as a single string. If you need to match more complex
patterns, look at the droptitleregex plugin instead.
Droptitleregex
feed2exec.plugins.droptitleregex.filter(*args, feed=None, item=None, **kwargs)
the droptitleregex filter will drop any feed item with a title matching the given
regular expression pattern.
Example:
[NASA breaking news]
url = https://www.nasa.gov/rss/dyn/breaking_news.rss
filter = feed2exec.plugins.droptitleregex
filter_args = ^ham
The above configuration processes the feed items based on the global configuration,
but it will skip any item whose title starts with the word “ham”.
Emptysummary
feed2exec.plugins.emptysummary.filter(*args, feed=None, item=None, **kwargs)
example of fixes for a broken feed, in this case, the GitHub release feed which
(sometimes) sends empty contents, in which case the item link field is used as a
summary instead.
Html2text
class feed2exec.plugins.html2text.filter(*args, feed=None, item=None, **kwargs)
This filter plugin takes a given feed item and adds a content_plain field with the
HTML parsed as text.
IMPORTANT:
the html2text plugin is called automatically from the email output plugins and
should normally not be called directly.
static parse(html=None)
parse html to text according to our preferences. this is where subclasses
can override the HTML2Text settings or use a completely different parser
Ikiwiki Recentchanges
feed2exec.plugins.ikiwiki_recentchanges.filter(*args, item=None, **kwargs)
the ikiwiki_recentchanges plugin fixes links in ikiwiki feeds
Ikiwiki recent changes show all the recent edits to pages, but the <link> element
doesn’t point to the edit page: it points to the recent changes page itself, which
make them useless for link checking or archival purposes.
This parses the recent changes entries and extracts the relevant links from it.
An alternative to this is to use the following entry to generate a special feed in
Ikiwiki:
[[!inline pages="*" feeds=yes feedonly=yes feedfile=archive show=10]]
This generates a feed with proper <link> elements but requires write access to the
wiki.
This will also add the date to the URL GUID so that we refresh when a page is
updated. Otherwise feed2exec would think the entry has already been passed.
Matchtitleregex
feed2exec.plugins.matchtitleregex.filter(*args, feed=None, item=None, **kwargs)
The matchtitleregex filter selects only the feed items whose title match the given
regular expression pattern.
Example:
[NASA breaking news]
url = https://www.nasa.gov/rss/dyn/breaking_news.rss
filter = feed2exec.plugins.matchtitleregex
filter_args = ^spam
The above configuration processes the feed items based on the global configuration,
but it will skip any item whose title does not start with the word “spam”.
WRITING NEW PLUGINS
Most of the actual work in the program is performed by plugins. A plugin is a simple
Python module that has a output or filter “callable” (function or class) with a predefined
interface.
Basic plugin principles
To write a new plugin, you should start by creating a simple Python module, in your
PYTHONPATH. You can find which directories are in the path by calling:
$ python3 -c "import sys; print(sys.path)"
['', '/usr/lib/python35.zip', '/usr/lib/python3.5', '/usr/lib/python3.5/plat-x86_64-linux-gnu', '/usr/lib/python3.5/lib-dynload', '/usr/local/lib/python3.5/dist-packages', '/usr/lib/python3/dist-packages']
In the above example, a good location would be /usr/local/lib/python3.5/dist-packages. The
naming convention is loose: as long as the plugin matches the expected API, it should just
work. For the purpose of this demonstration, we’ll call our plugin trumpery, so we will
create the plugin code like this:
touch /usr/local/lib/python3.5/dist-packages/trumpery.py
Naturally, if you are going to write multiple plugins, you may want to regroup your
multiple plugins in a package, see the module documentation for more information about
this concept in Python.
NOTE:
There is a rudimentary plugin resolution process that looks for plugins first in the
feed2exec.plugins namespace but then globally. This is done in
feed2exec.plugins.resolve(), called from the add and parse commands. This means that
the absolute path is expected to be used in the configuration file and internally.
You are welcome to distribute plugins separately or send them as merge requests, see
Contribution guide for more information on how to participate in this project. We of
course welcome contributions to this documentation as well!
Filters
Now, you need your plugin to do something. In our case, let’s say we’d like to skip any
feed entry that has the word Trump in it. For that purpose, we’ll create a plugin similar
to the already existing feed2exec.plugins.droptitle plugin, but that operates on the body
of the feed, but that also hardcodes the word, because this is just a demonstration and we
want to keep it simple. Let’s look at the title plugin to see how it works:
def filter(*args, feed=None, item=None, **kwargs):
'''the droptitle filter will drop any feed item with a title matching
the given args.
Example::
[NASA breaking news]
url = https://www.nasa.gov/rss/dyn/breaking_news.rss
filter = feed2exec.plugins.droptitle
filter_args = Trump
The above will process the feed items according to the global
configuration, but will skip any item that has the word "Trump"
anywhere in the title field.
Arguments are processed as a single string. If you need to match
more complex patterns, look at the droptitleregex plugin instead.
'''
item['skip'] = ' '.join(args) in item.get('title', '')
That may look like complete gibberish to you if you are not familiar with programming or
with Python programming in particular. But let’s take this from the top and copy that in
our own plugin. The first line declares a function that takes at least a feed and a item
argument, but can also accept any other arbitrary argument. This is important because we
want to have the plugin keep on working if the plugin API changes in the future. This is
called “forward-compatibility”. So let’s copy that in our plugin and add a pass statement
to make sure the plugin works (even if it does nothing for now):
def filter(*args, feed=None, item=None, **kwargs):
pass
We can already test our plugin by adding it to our configuration, in
~/.config/feed2exec.ini:
[NASA]
url = https://www.nasa.gov/rss/dyn/breaking_news.rss
output = feed2exec.plugins.echo
args = {item.title}
filter = trumpery
Notice how we use the output plugin to show the title of feed items selected, as a
debugging tool. Let’s fetch this feed in debugging mode to see what happens:
$ python3 -m feed2exec --verbose fetch --force
opening local file /home/anarcat/src/feed2exec/feed2exec/tests/files/breaking_news.xml
parsing feed file:///home/anarcat/src/feed2exec/feed2exec/tests/files/breaking_news.xml (10355 bytes)
connecting to database at ./doc/feed2exec.db
arguments received: ('President Trump Welcomes Home Record-breaking NASA Astronaut Peggy Whitson',)
arguments received: ('Three International Space Station Crewmates Safely Return to Earth',)
arguments received: ('NASA Statement on Nomination for Agency Administrator',)
arguments received: ('NASA Television to Air Return of Three International Space Station Crew Members',)
arguments received: ('NASA and Iconic Museum Honor Voyager Spacecraft 40th Anniversary',)
arguments received: ('NASA’s Johnson Space Center Closes Through Labor Day for Tropical Storm Harvey',)
arguments received: ('NASA Cancels Planned Media Availabilities with Astronauts',)
arguments received: ('NASA Awards $400,000 to Top Teams at Second Phase of 3D-Printing Competition',)
arguments received: ('NASA Awards Contract for Center Protective Services for Glenn Research Center',)
arguments received: ('NASA Announces Cassini End-of-Mission Media Activities',)
1 feeds processed
Good! The feed is fetched and items are displayed. It means our filter didn’t interfere,
but now it’s time to make it do something. To skip items, we need to set the skip
attribute for the feed item to True if we want to skip it and False otherwise. So we’ll
use a simple recipe, a bit like droptitle does, but simpler, to look at the feed content
to look for our evil word. The feedparser documentation tells us feed items have a summary
field which we can inspect. There’s also a content list, but that’s a little more
complicated so we’ll skip that for now. So, let’s set the skip parameter to match if there
is the evil word in our feed item, like this:
def filter(*args, feed=None, item=None, **kwargs):
item['skip'] = 'Trump' in item.get('summary', '')
And let’s see the result (note that we use the --force argument here otherwise we would
just skip all items because of the cache):
$ python3 -m feed2exec --verbose fetch --force
opening local file /home/anarcat/src/feed2exec/feed2exec/tests/files/breaking_news.xml
parsing feed file:///home/anarcat/src/feed2exec/feed2exec/tests/files/breaking_news.xml (10355 bytes)
connecting to database at ./doc/feed2exec.db
item President Trump Welcomes Home Record-breaking NASA Astronaut Peggy Whitson of feed NASA filtered out
arguments received: ('Three International Space Station Crewmates Safely Return to Earth',)
item NASA Statement on Nomination for Agency Administrator of feed NASA filtered out
arguments received: ('NASA Television to Air Return of Three International Space Station Crew Members',)
arguments received: ('NASA and Iconic Museum Honor Voyager Spacecraft 40th Anniversary',)
arguments received: ('NASA’s Johnson Space Center Closes Through Labor Day for Tropical Storm Harvey',)
arguments received: ('NASA Cancels Planned Media Availabilities with Astronauts',)
arguments received: ('NASA Awards $400,000 to Top Teams at Second Phase of 3D-Printing Competition',)
arguments received: ('NASA Awards Contract for Center Protective Services for Glenn Research Center',)
arguments received: ('NASA Announces Cassini End-of-Mission Media Activities',)
1 feeds processed
Success! We have skipped the two items that contain the fraud we wanted to remove from the
world. Notice how we were able to modify the feed item: we can also use that to change the
feed content. Normally, we would use this to fix malformed feeds, but let’s have some fun
instead and rename Trump to Drumpf:
def filter(*args, feed=None, item=None, **kwargs):
item['title'] = item.get('title', '').replace('Trump', 'Drumpf')
And the result:
$ python3 -m feed2exec --verbose fetch --force
opening local file /home/anarcat/src/feed2exec/feed2exec/tests/files/breaking_news.xml
parsing feed file:///home/anarcat/src/feed2exec/feed2exec/tests/files/breaking_news.xml (10355 bytes)
connecting to database at ./doc/feed2exec.db
arguments received: ('President Drumpf Welcomes Home Record-breaking NASA Astronaut Peggy Whitson',)
arguments received: ('Three International Space Station Crewmates Safely Return to Earth',)
arguments received: ('NASA Statement on Nomination for Agency Administrator',)
arguments received: ('NASA Television to Air Return of Three International Space Station Crew Members',)
arguments received: ('NASA and Iconic Museum Honor Voyager Spacecraft 40th Anniversary',)
arguments received: ('NASA’s Johnson Space Center Closes Through Labor Day for Tropical Storm Harvey',)
arguments received: ('NASA Cancels Planned Media Availabilities with Astronauts',)
arguments received: ('NASA Awards $400,000 to Top Teams at Second Phase of 3D-Printing Competition',)
arguments received: ('NASA Awards Contract for Center Protective Services for Glenn Research Center',)
arguments received: ('NASA Announces Cassini End-of-Mission Media Activities',)
1 feeds processed
I know, absolutely hilarious, right? More seriously, this is also how the
feed2exec.plugins.html2text filter works, which is enabled by default and helps the email
output plugin do its job by turning HTML into text. At this point, the only limit is your
knowledge of Python programming and your imagination!
Output plugins
Output plugins are another beast entirely. While they operate with the same principle than
filter plugins (search path and function signature are similar), they are designed to
actually output something for each new feed item found. This can be anything: a file,
email, HTTP request, whatever. If there is a commandline tool that does what you need, it
is probably simpler to just call the exec plugin and there are numerous examples of this
in the sample configuration file. For more complex things, however, it may be easier to
actually write this as a Python.
Basic arguments
For our example, we’ll write an archival plugin which writes each new entry to a file
hierarchy. First, we start with the same simple function signature as filters, except we
name it output:
def output(*args, feed=None, item=None, **kwargs):
pass
This is the equivalent of the null plugin and basically outputs nothing at all. To archive
the feed items, we’ll need to look at the link element feedparser gives us. Let’s see what
that looks like for the NASA feed:
def output(*args, feed=None, item=None, **kwargs):
# only operate on items that actually have a link
if item.get('link'):
print(item.get('link', ''))
else:
logging.info('no link for feed item %s, not archiving', item.get('title'))
NOTE:
Note that we try to make plugins silent in general. You can use logging.info() to have
things show up in --verbose and logging.debug() for --debug but by default, your plugin
should be silent unless there’s an error that requires the user’s intervention, in
which case you should use logging.warning() for transient errors that may be
automatically recovered and logging.error() for errors that require user intervention.
This is to allow users to ignore warnings safely.
Note that here we first check to see if the feed item actually has a link - not all feeds
do! After adding the above to our trumpery plugin and adding it as an output plugin:
[NASA]
url = https://www.nasa.gov/rss/dyn/breaking_news.rss
output = trumpery
filter = trumpery
We can try to see what happens when we call it:
$ python3 -m feed2exec --verbose fetch --force
opening local file /home/anarcat/src/feed2exec/feed2exec/tests/files/breaking_news.xml
parsing feed file:///home/anarcat/src/feed2exec/feed2exec/tests/files/breaking_news.xml (10355 bytes)
connecting to database at ./doc/feed2exec.db
http://www.nasa.gov/press-release/president-trump-welcomes-home-record-breaking-nasa-astronaut-peggy-whitson
http://www.nasa.gov/press-release/three-international-space-station-crewmates-safely-return-to-earth
http://www.nasa.gov/press-release/nasa-statement-on-nomination-for-agency-administrator
http://www.nasa.gov/press-release/nasa-television-to-air-return-of-three-international-space-station-crew-members
http://www.nasa.gov/press-release/nasa-and-iconic-museum-honor-voyager-spacecraft-40th-anniversary
http://www.nasa.gov/press-release/nasa-s-johnson-space-center-closes-through-labor-day-for-tropical-storm-harvey
http://www.nasa.gov/press-release/nasa-cancels-planned-media-availabilities-with-astronauts
http://www.nasa.gov/press-release/nasa-awards-400000-to-top-teams-at-second-phase-of-3d-printing-competition
http://www.nasa.gov/press-release/nasa-awards-contract-for-center-protective-services-for-glenn-research-center
http://www.nasa.gov/press-release/nasa-announces-cassini-end-of-mission-media-activities
1 feeds processed
Sanitizing contents
Good. Those are the URLs we want to save to disk. Let’s start by just writing those to a
file. We will also use a simple slug function to make a filesystem-safe name from the feed
title and save those files in a pre-determined location:
import logging
import os.path
from feed2exec.utils import slug
ARCHIVE_DIR='/run/user/1000/feed-archives/'
def output(*args, feed=None, item=None, session=None, **kwargs):
# make a safe path from the item name
path = slug(item.get('title', 'no-name'))
# put the file in the archive directory
path = os.path.join(ARCHIVE_DIR, path)
# only operate on items that actually have a link
if item.get('link'):
# tell the user what's going on, if verbose
# otherwise, we try to stay silent if all goes well
logging.info('saving feed item %s to %s from %s',
item.get('title'), path, item.get('link'))
# open the file
with open(path, 'w') as archive:
# write the response
archive.write(item.get('link'))
else:
logging.info('no link for feed item %s, not archiving', item.get('title'))
Now I know this may look like a huge step from the previous one but I’m sorry, I couldn’t
find a simpler second step. :) The output now looks like this:
$ python3 -m feed2exec --config ./doc/ --verbose fetch --force
opening local file /home/anarcat/src/feed2exec/feed2exec/tests/files/breaking_news.xml
parsing feed file:///home/anarcat/src/feed2exec/feed2exec/tests/files/breaking_news.xml (10355 bytes)
connecting to database at ./doc/feed2exec.db
saving feed item President Drumpf Welcomes Home Record-breaking NASA Astronaut Peggy Whitson to /run/user/1000/president-drumpf-welcomes-home-record-breaking-nasa-astronaut-peggy-whitson from http://www.nasa.gov/press-release/president-trump-welcomes-home-record-breaking-nasa-astronaut-peggy-whitson
saving feed item Three International Space Station Crewmates Safely Return to Earth to /run/user/1000/three-international-space-station-crewmates-safely-return-to-earth from http://www.nasa.gov/press-release/three-international-space-station-crewmates-safely-return-to-earth
saving feed item NASA Statement on Nomination for Agency Administrator to /run/user/1000/nasa-statement-on-nomination-for-agency-administrator from http://www.nasa.gov/press-release/nasa-statement-on-nomination-for-agency-administrator
saving feed item NASA Television to Air Return of Three International Space Station Crew Members to /run/user/1000/nasa-television-to-air-return-of-three-international-space-station-crew-members from http://www.nasa.gov/press-release/nasa-television-to-air-return-of-three-international-space-station-crew-members
saving feed item NASA and Iconic Museum Honor Voyager Spacecraft 40th Anniversary to /run/user/1000/nasa-and-iconic-museum-honor-voyager-spacecraft-40th-anniversary from http://www.nasa.gov/press-release/nasa-and-iconic-museum-honor-voyager-spacecraft-40th-anniversary
saving feed item NASA’s Johnson Space Center Closes Through Labor Day for Tropical Storm Harvey to /run/user/1000/nasa-s-johnson-space-center-closes-through-labor-day-for-tropical-storm-harvey from http://www.nasa.gov/press-release/nasa-s-johnson-space-center-closes-through-labor-day-for-tropical-storm-harvey
saving feed item NASA Cancels Planned Media Availabilities with Astronauts to /run/user/1000/nasa-cancels-planned-media-availabilities-with-astronauts from http://www.nasa.gov/press-release/nasa-cancels-planned-media-availabilities-with-astronauts
saving feed item NASA Awards $400,000 to Top Teams at Second Phase of 3D-Printing Competition to /run/user/1000/nasa-awards-400-000-to-top-teams-at-second-phase-of-3d-printing-competition from http://www.nasa.gov/press-release/nasa-awards-400000-to-top-teams-at-second-phase-of-3d-printing-competition
saving feed item NASA Awards Contract for Center Protective Services for Glenn Research Center to /run/user/1000/nasa-awards-contract-for-center-protective-services-for-glenn-research-center from http://www.nasa.gov/press-release/nasa-awards-contract-for-center-protective-services-for-glenn-research-center
saving feed item NASA Announces Cassini End-of-Mission Media Activities to /run/user/1000/nasa-announces-cassini-end-of-mission-media-activities from http://www.nasa.gov/press-release/nasa-announces-cassini-end-of-mission-media-activities
Sweet! Now it’s not really nice to save this in /run/user/1000. I just chose this
directory because it was a safe place to write but it’s not a persistent directory. Best
make that configurable, which is where plugin arguments come in.
User configuration
You see that *args parameter? That comes straight from the configuration file. So you
could set the path in the configuration file, like this:
[NASA]
url = https://www.nasa.gov/rss/dyn/breaking_news.rss
output = trumpery
args = /srv/archives/nasa/
filter = trumpery
We also need to modify the plugin to fetch that configuration, like this:
def output(*args, feed=None, item=None, session=None, **kwargs):
# make a safe path from the item name
path = slug(item.get('title', 'no-name'))
# take the archive dir from the user or use the default
archive_dir = ' '.join(args) if args else DEFAULT_ARCHIVE_DIR
# put the file in the archive directory
path = os.path.join(archive_dir, path)
# [...]
# rest of the function unchanged
Making HTTP requests
And now obviously, we only saved the link itself, not the link content. For that we need
some help from the requests module, and do something like this:
# fetch the URL in memory
result = session.get(item.get('link'))
if result.status_code != requests.codes.ok:
logging.warning('failed to fetch link %s: %s',
item.get('link'), result.status_code)
# make sure we retry next time
return False
# open the file
with open(path, 'w') as archive:
# write the response
archive.write(result.text)
This will save the actual link content (result.text) to the file. The important statement
here is:
# fetch the URL in memory
result = session.get(item.get('link'))
which fetches the URL in memory and checks for errors. The other change in the final
plugin is simply:
archive.write(result.text)
which writes the article content instead of the link.
Notice how the session argument is used here instead of talking directly to the requests
module. This leverages a caching system we already have, alongside configuration like
user-agent and so on.
Plugin return values
Notice how we return False here: this makes the plugin system avoid adding the item to the
cache, so it is retried on the next run. If the plugin returns True or nothing (None), the
plugin is considered to have succeeded and the entry is added to the cache. That logic is
defined in feed2exec.controller.FeedManager.fetch().
Catchup
A final thing that is missing that is critical in all plugins is to respect the catchup
setting. It is propagated up from the commandline or configuration all the way down to
plugins, through the feed parameters. How you handle it varies from plugin to plugin, but
the basic idea is to give feedback (when verbose) of activity when the plugin is run but
to not actually do anything. In our case, we simply return success, right before we fetch
the URL:
if feed.get('catchup'):
return True
# fetch the URL in memory
result = session.get(item.get('link'))
Notice how we still fetch the actual feed content but stop before doing any permanent
operation. That is the spirit of the “catchup” operation: we not only skip “write”
operation, but also any operation which could slow down the “catchup”: fetching stuff over
the network takes time and while it can be considered a “readonly” operation as far as the
local machine is concerned, we are effectively writing to the network so that operation
shouldn’t occur.
Hopefully that should get you going with most of the plugins you are thinking of writing!
Writing tests
Writing tests is essential in ensuring that the code will stay maintainable in the future.
It allows for easy refactoring and can find bugs that manual testing may not, especially
when you get complete coverage (although that is no guarantee either).
We’ll take our archive plugin as an example. The first step is to edit the
tests/test/test_plugins.py file, where other plugins are tests as well. We start by
creating a function named test_archive so that Pytest, our test bed, will find it:
def test_archive(tmpdir, betamax): # noqa
pass
Notice the two arguments named tmpdir and betamax. Both of those are fixtures, a pytest
concept that allows to simulate an environment. In particular, the tmpdir fixture, shipped
with pytest, allows you to easily manage (and automatically remove) temporary directories.
The betamax fixtures is a uses the betamax module to record then replay HTTP requests.
Then we need to do something. We need to create a feed and a feed item that we can then
send into the plugin. We could also directly parse an existing feed and indeed some
plugins do exactly that. But our plugin is simple and we can afford to skip full feed
parsing and just synthesize what we need:
feed = Feed('test archive', test_sample)
item = feedparser.FeedParserDict({'link': 'http://example.com/',
'title': 'example site'})
This creates a new feed based on the test_sample feed. This is necessary so that the
session is properly re-initialized in the feed item (otherwise the betamax fixture will
not work). Then it creates a fake feed entry simply with one link and a title. Then we can
call our plugin, and verify that it saves the file as we expected. The test for the most
common case looks like this:
def test_archive(tmpdir, betamax): # noqa
dest = tmpdir.join('archive')
feed = Feed('test archive', test_sample)
item = feedparser.FeedParserDict({'link': 'http://example.com/',
'title': 'example site'})
assert archive_plugin.output(str(dest), feed=feed, item=item)
assert dest.join('example-site').check()
Then we can try to run this with pytest-3:
[1084]anarcat@curie:feed2exec$ pytest-3
=============================== test session starts ===============================
platform linux -- Python 3.5.3, pytest-3.0.6, py-1.4.32, pluggy-0.4.0
rootdir: /home/anarcat/src/feed2exec, inifile: setup.cfg
plugins: profiling-1.2.11, cov-2.4.0, betamax-0.8.0
collected 26 items
feed2exec/utils.py ..
feed2exec/plugins/transmission.py .
feed2exec/tests/test_feeds.py ........
feed2exec/tests/test_main.py .....
feed2exec/tests/test_opml.py .
feed2exec/tests/test_plugins.py .........
----------- coverage: platform linux, python 3.5.3-final-0 -----------
Name Stmts Miss Cover
----------------------------------------------------------------
feed2exec/__init__.py 12 0 100%
feed2exec/__main__.py 87 1 99%
feed2exec/_version.py 1 0 100%
feed2exec/email.py 81 7 91%
feed2exec/feeds.py 243 8 97%
feed2exec/logging.py 31 11 65%
feed2exec/plugins/__init__.py 47 6 87%
feed2exec/plugins/archive.py 23 5 78%
feed2exec/plugins/droptitle.py 2 0 100%
feed2exec/plugins/echo.py 8 0 100%
feed2exec/plugins/emptysummary.py 5 0 100%
feed2exec/plugins/error.py 2 0 100%
feed2exec/plugins/exec.py 7 0 100%
feed2exec/plugins/html2text.py 20 4 80%
feed2exec/plugins/ikiwiki_recentchanges.py 9 5 44%
feed2exec/plugins/maildir.py 28 0 100%
feed2exec/plugins/mbox.py 29 1 97%
feed2exec/plugins/null.py 5 1 80%
feed2exec/plugins/transmission.py 20 0 100%
feed2exec/plugins/wayback.py 20 0 100%
feed2exec/tests/__init__.py 0 0 100%
feed2exec/tests/conftest.py 3 0 100%
feed2exec/tests/fixtures.py 19 0 100%
feed2exec/tests/test_feeds.py 124 0 100%
feed2exec/tests/test_main.py 90 0 100%
feed2exec/tests/test_opml.py 17 0 100%
feed2exec/tests/test_plugins.py 162 0 100%
feed2exec/utils.py 41 12 71%
----------------------------------------------------------------
TOTAL 1136 61 95%
=========================== 26 passed in 10.83 seconds ============================
Notice the test coverage: we only have 78% test coverage for our plugin. This means that
some branches of the code were not executed at all! Let’s see if we can improve that.
Looking at the code, I see there are some conditionals for error handling. So let’s
simulate an error, and make sure that we don’t create a file on error:
dest.remove()
item = feedparser.FeedParserDict({'link': 'http://example.com/404',
'title': 'example site'})
assert not archive_plugin.output(str(dest), feed=feed, item=item)
assert not dest.join('example-site').check()
There. Let’s see the effect on the test coverage:
[1085]anarcat@curie:feed2exec2$ pytest-3 feed2exec/tests/test_plugins.py::test_archive
=============================== test session starts ===============================
platform linux -- Python 3.5.3, pytest-3.0.6, py-1.4.32, pluggy-0.4.0
rootdir: /home/anarcat/src/feed2exec, inifile: setup.cfg
plugins: profiling-1.2.11, cov-2.4.0, betamax-0.8.0
collected 10 items
feed2exec/tests/test_plugins.py .
----------- coverage: platform linux, python 3.5.3-final-0 -----------
Name Stmts Miss Cover
----------------------------------------------------------------
feed2exec/__init__.py 12 0 100%
feed2exec/__main__.py 87 87 0%
feed2exec/_version.py 1 0 100%
feed2exec/email.py 81 64 21%
feed2exec/feeds.py 243 172 29%
feed2exec/logging.py 31 31 0%
feed2exec/plugins/__init__.py 47 38 19%
feed2exec/plugins/archive.py 23 3 87%
feed2exec/plugins/droptitle.py 2 2 0%
feed2exec/plugins/echo.py 8 3 62%
feed2exec/plugins/emptysummary.py 5 5 0%
feed2exec/plugins/error.py 2 2 0%
feed2exec/plugins/exec.py 7 7 0%
feed2exec/plugins/html2text.py 20 13 35%
feed2exec/plugins/ikiwiki_recentchanges.py 9 9 0%
feed2exec/plugins/maildir.py 28 19 32%
feed2exec/plugins/mbox.py 29 29 0%
feed2exec/plugins/null.py 5 5 0%
feed2exec/plugins/transmission.py 20 12 40%
feed2exec/plugins/wayback.py 20 20 0%
feed2exec/tests/__init__.py 0 0 100%
feed2exec/tests/conftest.py 3 0 100%
feed2exec/tests/fixtures.py 19 6 68%
feed2exec/tests/test_feeds.py 124 101 19%
feed2exec/tests/test_main.py 90 90 0%
feed2exec/tests/test_opml.py 17 17 0%
feed2exec/tests/test_plugins.py 166 123 26%
feed2exec/utils.py 41 16 61%
----------------------------------------------------------------
TOTAL 1140 874 23%
============================ 1 passed in 2.46 seconds =============================
Much better! Only 3 lines left to cover!
NOTE:
Notice how I explicitly provided a path to my test. This is entirely optional. You can
just run pytest-3 and it will run the whole test suite: this method is just faster.
Notice also how the coverage ratio is very low: this is normal; we are testing, after
all, only one plugin here.
The only branches left to test in the code is the other possible error (“no link in the
feed”) and to test the “catchup” mode. You can see this in the actual test_plugins.py file
distributed with this documentation.
NOTE:
If you discover a bug associated with a single feed, you can use the betamax session
and the feed2exec.model.Feed.parse() function to manually parse a feed and fire your
plugin. This is how email functionality is tested: see the
feed2exec.tests.test_plugins.test_email() function for an example.
SEE ALSO
feed2exec(1)
AUTHOR
Antoine Beaupré
COPYRIGHT
Copyright (C) 2016-2019 Antoine Beaupré