Architecture Overview
PyBlosxom is implemented as a pipeline of plugins. The input to the pipeline is an HTTP request and the output is an HTTP response (most commonly containing HTML or RSS/Atom). There are abstractions to represent the HTTP request and response, the configuration information, the entries and other data stored in PyBlosxom.
In PyBlosxom, a plugin is a Python module. You define functions in the module, and PyBlosxom will call functions with a specific name at a well-defined point in the execution of the PyBlosxom pipeline. For example, a callback function named cb_start is called before most PyBlosxom processing begins. If your plugin module provides a function called cb_start, then it will be called.
PyBlosxom allows you to install many plugins, so a natural question is how do all those plugins interact. The py['load_plugins'] list serve two purposes. It tells PyBlosxom which plugins in the various plugin directories will actually get used. It also defines a sequential order in which plugins will be called. If you don't provide a value for py['load_plugins'] (you must still provide a value for py['plugin_dirs'] if you want to use any plugins), then PyBlosxom will load all the modules in all the plugin directories specified in py['plugin_dirs']. The plugins will be sorted by alphanumeric sorting on their names, and that will be the order in which they are called.
At a given callback point, every module function which provides a correctly named function will be called. So if you load five plugin modules and each module provides a cb_start function, then all five functions will be called when PyBlosxom reaches the start callback point. The order in which those five functions are called will be determined by the rules described in the previous paragraph. This allows multiple plugins to get access to data at the proper point during PyBlosxom's execution. It also allows plugins to exchange information if they know their relative ordering (it's best to use py['load_plugins'] in this case.)
For advanced usage, it is possible to change the way that chains of callback functions are processed. So instead of calling every callback function in the chain, it's possible to arrange for a particular callback chain to work differently. The cb_handle callback chain gives each callback function in the chain a chance to try processing data. If the callback is successful then none of the remaining callback functions in the chain will execute.
When a callback function is called it is passed a dictionary that contains the information in the HTTP request, the information from the configuration file, and any data that may exist in PyBlosxom at that point in time (usually a list of weblog entries). I'll be referring to this dictionary as the "args dictionary' in the rest of this document.
Here's a skeleton of a start callback function -- remember that all callbacks are prefixed with cb_.
def cb_start(args):
request = args['request'] # get the argument dictionary
config = request.getConfiguration() # config file information
http = request.getHttp() # HTTP header information
cgi_form = http['form'] # including any CGI form
data = request.getData() # the rest of the data
[23:19] | [] | #-permalink-#