Provided by: feed2exec_0.15.0_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