HOWTO-gfalPlugin

How to create a new method on a gfal plugin.

The example used here will be with adding a QoS method on the http plugin
You can checkout the commit doing so here: https://gitlab.cern.ch/dmc/gfal2/commit/87ca30684d1e85c59edafa7935e830b9006f054f

1) Choose the plugin you want to extend and create a new file that will hold the methods to be created
    ex:  a) Create the src/plugins/http/gfal_http_qos.cpp file
         b) Create the gfal_http_check_classes method

2) The new method created has to be declared on the src/plugins/http/gfal_http_plugin.h file

3) Since this method will be a plugin method, it needs to be added to the interface of the plugins
   here: src/core/common/gfal_plugin_interface.h

   A new mode has to be created for it as well (check example at gfal_plugin_interface.h)
   In our case, GFAL_PLUGIN_QOS_CHECK_CLASSES will have to be added

   A new method to generically access this plugin function has to be declared on this file:
   gfal_plugin_qos_check_classes in our case.

4) The aforementioned method has to be implemented on src/core/common/gfal_plugin.c

5) Since the methods before implement the functionality of distinguishing between plugins, another method has to be declared and used for generic
   usage of what we want to do. This is done at src/core/file/gfal_file_api.h  and src/core/file/gfal2_standard_file_operations.c

6) We finally need to define the actual plugin behavior when this method is requested. This is done at: src/plugins/http/gfal_http_plugin.cpp
   There, is also defined if this plugin supports this specific behavior (GFAL_PLUGIN_QOS_CHECK_CLASSES in our case).

7) A functional test needs to be created in order to test these:
    a) Create the test at: test/functional/gfal_test_qos.cpp
    b) Declare the test at: test/functional/CMakeLists.txt and then test/functional/functional-test-parameters.cmake

Complete example at https://gitlab.cern.ch/dmc/gfal2/commit/87ca30684d1e85c59edafa7935e830b9006f054f