.. _services-debug:

Debugging ZOO Services
=========================

Several methods can be used in order to debug :ref:`services_index`. The most common solutions are web or command line.

Web
----

Any problem can be checked in the Apache server log file when using http WPS requests.

On Unix, the log files is usually located in ``/var/log/apache2`` and
the relevant one is named *error_log*. A simple way to read this file is to use the ``tail`` command,
as it allows to see the file updates for each request ::

  tail -f /var/log/apache2/error_log

If the log is not clear enough, you still have the possibility to add
more debug information to your source code, writing to standard errors.

Python
********
Using Python, you can for example do this:

.. code-block:: python

  import sys
  
  #add this line when you want see an own message
  sys.stderr.write("My message")

.. _web_javascript:

Javascript
************

Using JavaScript, you can use ``alert`` to print a string to standard error, for example:

.. code-block:: javascript

  // add this line when you want to see own message
  alert('My message')
  // you can debug value of inputs, outputs or conf
  alert(inputs["S"]["value"])

.. note:: If you try to pass an object it will only return ``[object Object]``

Command line
--------------

:ref:`kernel_index` (*zoo_loader.cgi*) can also be used from command line. This is really useful for debugging services in a deeper way, for example:.

.. code-block:: bash

  # in order to use it you have to copy test_service.py and HelloPy.zcfg from
  # the example services
  ./zoo_loader.cgi "service=wps&version=1.0.0&request=execute&identifier=HelloPy&datainputs=a=your name&responsedocument=Result"

Working this way you can use the standard debug system of the actual programming language used
to develop your service.

GDB
*****
From command line you can use also the command line tool `GDB <http://www.gnu.org/software/gdb/>`_
to debug ``zoo_loader.cgi``, you have to run:

.. code-block:: bash

  # launch zoo_loader.cgi from gdb
  gdb zoo_loader.cgi
  # now run your request
  run "service=wps&version=1.0.0&request=execute&identifier=HelloPy&datainputs=a=your name&responsedocument=Result"

At this point you can ask help at the `ZOO mailing list <http://lists.osgeo.org/cgi-bin/mailman/listinfo/zoo-discuss>`_
copying the result of the command.

Python
**********
For Python, you can use ``pdb``, more info at http://docs.python.org/2/library/pdb.html

.. code-block:: python

  import pdb
  
  # add this line when you want investigate your code in more detail
  pdb.set_trace()

Javascript
************

You can use ``alert`` also to print in the console, more info in the :ref:`web_javascript` web section