When does journald-native work better?
######################################

:category:  Ruby
:tags:      systemd, systemd-journal, journald-native, ruby gems, my projects
:date:      2016-04-05 01:20:00 +03:00

There is already a nice gem called ``systemd-journal``,
why another one? Well, because there are some edge cases that it does
not cover. I had a trouble with one.

.. TEASER_END

Imagine that your site can receive some arbitrary data from user.

.. code-block:: ruby

   received_message = "HAHA I'M HAXXOR! \\0 SOME CORRUPT DATA"

Then you try to parse it. This will fail with many libraries
written in C, JSON for example.

.. code-block:: ruby

   we_need_this_data = JSON["[#{received_message}]"]
   # JSON::ParserError: 399: unexpected token at 'HAHA I'M HAXXOR! '

Then we try to log it. Our logger uses ``systemd-journal``:

.. code-block:: ruby

   Systemd::Journal.message(
       priority: Systemd::Journal::LOG_WARNING,
       message:  "Parser failed on some data",
       data:     received_message,
   )
   # ArgumentError: string contains null byte
   #    from .../gems/ffi-1.9.10/lib/ffi/variadic.rb:56:in `invoke'
   #    from .../gems/ffi-1.9.10/lib/ffi/variadic.rb:56:in `call'
   #    from (eval):3:in `sd_journal_send'
   #    from .../gems/systemd-journal-1.2.0/lib/systemd/journal/writable.rb:78:in `message'

Whoops! We crashed the logger! Our logger is affected too!
Let's try ``journald-native``:

.. code-block:: ruby

   Journald::Native.send(
       "PRIORITY=#{Journald::LOG_WARNING}",
       "MESSAGE=Parser failed on some data",
       "DATA=#{received_message}",
   )
   # => 0

OMG! It works! Let's see what is saved.

.. code-block:: bash

   journalctl -o json-pretty

.. code-block:: json

   {
       "PRIORITY" : "4",
       "SYSLOG_IDENTIFIER" : "irb",
       "MESSAGE" : "Parser failed on some data",
       "DATA" : [
           72, 65, 72, 65, 32, 73, 39, 77, 32, 72, 65, 88, 88, 79, 82, 33,
           32, 0,  32, 83, 79, 77, 69, 32, 67, 79, 82, 82, 85, 80, 84, 32,
           68, 65, 84, 65
       ]
   }

Our corrupt message is saved as a byte sequence which we can analyze now.

`Next post <link://slug/ruby-strings-in-c-ext>`_
will be about correct handling of Ruby strings in C extensions.