Apache Rivet HTTP Request Processing
Tcl Scripts Processing The mod_rivet &version2-series; modules handle an HTTP request by running a Tcl script or a Rivet (.rvt file) template whose path appears encoded in the URI (an alias translation or URL rewriting might occur to establish the real path). The execution of such scripts can be preceded and/or followed by the execution scripts common to every path configured through the BeforeScript and AfterScript directives. These scripts can be configured on a per virtual host, per directory or per user basis. Execution of such combined scripts can break because of coding errors (thus triggering the ErrorScript execution) or it can deliberately interrupt ordinary execution by calling ::rivet::abort_page (triggering the execution of a script defined by the directive AbortScript). This scheme is in case terminated by a further configurable script (AfterEveryScript). In mod_rivet &version2-generic; module series this model of request handling was coded within the module mod_rivet.so itself. With Rivet &version30; we changed this approach and landed to a new much simpler and flexible model where each request is by default handled by the following Tcl procedure &request_handler.tcl; Note the call to new &version30; command ::rivet::url_script that returns the body of the Tcl script or Rivet template pointed by the URL. This procedure emulates the &version2-generic; scheme and as such works as a fully compatible request handling but opens to the programmers the option of replacing it with their own application request handling procedure Note that if you redefine the core request handler you'll need to handle yourself any error conditions and any code interruption brought about by calling ::rivet::abort_page. The current procedure might work as a template to be reworked and used as a template to develop your own request handler.
Example: basic OO Rivet Application An applications may have no interest in running a script pointed by the URL as in the traditional approach followed by rivet inspired to the PHP philosophy of scripting the HTML. A web based application could be driven entirely by the URL encoded arguments and by the data POSTed with HTML forms, still retaining the ability of exploiting the template engine of Rivet through the ::rivet::parse. In other words an application could hinge on a single entry point to handle requests, regardless the complexity of its internal design. This section shows a template for such an application (let's call it MyRivetApp) based on an Itcl (or TclOO for what it matters) object instance. In myrivetapp.tcl the application class is defined and an instance of it is created in the global namespace. &myrivetapp.tcl; which provides a very basic interface for both initialization and request processing. Such script will be sourced into the Tcl interpreter at the mod_rivet initialization stage. In the Apache configuration (most likely within a <VirtualHost myrivetapp.com:80>...</VirtualHost> definition block) <IfModule rivet_module> RivetServerConf ChildInitScript "source myrivetapp.tcl" </IfModule> By running this script when an a thread is started we set it up to respond requests, but we still need to tell mod_rivet what code will eventually handle requests and how the method MyRivetApp::request_processing will be called with appropriate arguments &myapp_request_handler.tcl;
Finally we have to tell mod_rivet to run this script when a request is delivered to myApplication and we do so using the &version30; directive RequestHandler <IfModule rivet_module> RivetServerConf ChildInitScript "source myrivetapp.tcl" RivetServerConf RequestHandler "myapp_request_handler.tcl" </IfModule> Notice that the argument of the directive RequestHandler is a file name not a Tcl script as for ChildInitScript With such approach only the ChildInitScript, ChildExitScript and GlobalInitScript configuration directives are effective, while the effect of other handler is devolved to our request handler script.