Provided by: feed2exec_0.14.0_all bug

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, **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.

              alias of feed2exec.plugins.echo.output

   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 Whats 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, **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.

              Example:

                 [NASA IOTD wayback]
                 url = https://www.nasa.gov/rss/dyn/lg_image_of_the_day.rss
                 output = feed2exec.plugins.wayback

              The above will save the Image of the day updates to the wayback machine.

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.

   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.

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
       contribute  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.
              '''
              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

       Successs! 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, **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, **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 = requests.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 = requests.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.

   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.feeds.parse().

   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 = requests.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 garantee 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.feeds.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  Antoine Beaupré