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.. -*- mode: rst -*-
.. _development-client-driver:
Writing A Client Tool Driver
============================
This page describes the step-by-step process of writing a client tool
driver for a configuration element type. The included example describes
an existing driver, and the process that was used to create it.
#. Pick a name for the driver. In this case, we picked the name RPM.
#. Add "RPM" to the ``__all__ list`` in ``src/lib/Client/Tools/__init__.py``
#. Create a file in ``src/lib/Client/Tools`` with the same name (RPM.py)
#. Create a class in this file with the same name (``class RPM``)
* If it handles ``Package`` entries, subclass ``Bcfg2.Client.Tools.PkgTool``
(from here referenced as branch [P])
* If it handles ``Service`` entries, subclass ``Bcfg2.Client.Tools.SvcTool``
(from here referenced as branch [S])
* Otherwise, ``subclass Bcfg2.Client.Tools.Tool`` (from here referenced
as branch [T])
#. Set ``__name__`` to "RPM"
#. Add any required executable programs to ``__execs__``
#. Set ``__handles__`` to a list of (``entry.tag``, ``entry.get('type')``)
tuples. This determines which entries the Tool module can be used
on. In this case, we set ``__handles__ = [('Package', 'rpm')]``.
#. Add verification. This method should return True/False depending
on current entry installation status.
* [T] Add a Verify<entry.tag> method.
* [P] Add a VerifyPackage method.
* [S] Add a VerifyService method.
* In the failure path, the current state of failing entry
attributes should be set in the entry, to aid in auditing.
(For example, if a file should be mode 644, and is currently
mode 600, then set attribute current_perms='600' in the input
entry)
#. Add installation support. This method should return True/False
depending on the results of the installation process.
* [T,S] Add an Install<entry.tag> method.
* [P] The PkgTool baseclass has a generic mechanism for performing
all-at-once installations, followed, in the case of failures,
by single installations. To enable this support, set the pkgtype
attribute to the package type handled by this driver. Set the
``pkgtool`` to a tuple ("command string %s", ("per-package string
format", [list of package entry fields])). For RPM, we have
``setup pkgtool = ("rpm --oldpackage --replacepkgs --quiet -U %s", ("%s", ["url"]))``
#. Implement entry removal
* [T,S] Implement a ``Remove`` method that removes all specified
entries (``prototype Remove(self, entries)``)
* [P] Implement a ``RemovePackages`` that removes all specified
entries (same prototype as Remove)
#. Add a ``FindExtra`` method that locates entries not included in the
configuration. This may or may not be required, certain drivers
do not have the capability to find extra entries.
#. [P] Package drivers require a ``RefreshPackages`` method that updates
the internal representation of the package database.
Writing Tool Driver Methods
---------------------------
#. Programs can be run using ``self.cmd.run``. This function returns a
(return code, stdout list) tuple.
#. The configuration is available as ``self.config``
#. Runtime options are available in a dictionary as ``self.setup``
#. Informational, error, and debug messages can be produced by
running ``self.logger.info/error/debug``.
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