Wombat 0.7.1

Wombat is a servlet container for Perl. It is not an executable program itself; rather, it is a library that can be used by programs to embed a servlet container. Embedding programs must provide implementations of Connector API classes that adapt Wombat to the surrounding environment. One such connector is Apache::Wombat which embeds a Wombat servlet container within an Apache httpd built with mod_perl.

Currently no developer documentation for Wombat itself is provided beyond the contents of this document and the POD for each Wombat class.

CONTAINER CONFIGURATION

CONTAINER DIRECTORIES

Web application directories are generally located beneath a single application base directory which in turn is usually located beneath the containers home directory. Each Host configured in the container can use the same application base directory (called webapps by default) or provide its own, possibly located outside the containers home directory. As well, each Application configured in the container has the option of locating its webapp directory outside its Hosts application base directory.

A typical directory structure for Wombat embedded within Apache/mod_perl might be:

# containers home dir
/usr/local/apache
# default hostss appbase dir
/usr/local/apache/webapps
# examples apps webapp dir
/usr/local/apache/webapps/examples
# another hosts appbase dir
/home/bcm/maz.org/webapps
# another apps webapp dir
/home/bcm/maz.org/webapps/comics

CONTAINER DEPLOYMENT DESCRIPTOR

The behavior and attributes of the Wombat servlet container are controlled by a container deployment descriptor (usually named server.xml). This file is modeled after the Tomcat 4 equivalent, but it does have slight differences. A full Configuration Guide will be published; until then, the definitions included below are the only documentation:

Elements supported in server.xml (named with XPath paths, example attribute settings included inline):

Server

Represents the entire perl interpreter, into which one or more Services are deployed. Only one Server may be specified.

Server/Service

Represents a collection of one or more Connectors that share a single Engine (and therefore the web applications visible within that Engine). A display name for the Service (name="HTTP Service") may be specified. Many Services may be specified for the single Server.

Server/Service/Connector

Represents an endpoint by which requests are received and responses are returned. Each Connector passes requests on to its associated Container for processing. The name of a class that implements the Wombat::Connector interface MUST be specified (className="Apache::Wombat::Connector"), as well as a scheme (scheme="http" attribute) and any attributes needed by the implementation. A secure flag (secure="1") may also be set to indicated that the request was transported using SSL. Many Connectors may theoretically be specified for a particular Service, but at this time, the Wombat internals need some refactoring before they can support Connectors for protocols other than HTTP.

Server/Service/Engine

Represents the highest level Container associated with a set of Connectors. The Engine discriminates between virtual hosts as necessary and passes the request along to the appropriate Host. A display name for the Engine (name="Apache-Wombat") may be specified, as well as the name of a default host (defaultHost="localhost" attribute) to receive requests that are not mapped to other specifically configured Hosts. Only one Engine may be specified for a particular Service.

Server/Service/Engine/Logger

Unless overridden in a lower level Container, all log messages will be handled by this Logger. The name of a class that implements the Wombat::Logger interface MUST be specified (className="Apache::Wombat::Logger"), as well as any attributes needed by the implementation. A minimum log level (level="DEBUG") may also be specified. If no Logger is specified, logging will be disabled for the Container. Only one Logger may be specified for a particular Container.

Server/Service/Engine/Realm

Unless overridden in a lower level Container, all web applications will be subject to this security Realm. The name of a class that implements the Wombat::Realm interface MUST be specified (className="Wombat::Realm::DBIRealm"), as well as any attributes needed by the implementation. If no Realm is specified, security will be disabled for the Container. Only one Realm may be specified for a particular Container.
Note that security MUST be also enabled in a particular web applications deployment descriptor in order for the Realm to be relevant to that web application. Therefore a Realm may be configured for an entire Container but only in use for a single Application.

Server/Service/Engine/SessionManager

Unless overridden in a lower level Container, all sessions will be managed by this SessionManager. The name of a class that implements the Wombat::SessionManager interface MUST be specified (className="Wombat::SessionManager::StandardSessionManager"), as well as any attributes needed by the implementation. A maximum inactivity interval/idle out time may also be specified (maxInactiveInterval="300"). If no SessionManager element is specified, sessions will be disabled for the Container. Only one SessionManager may be specified for a particular Container.

The type of SessionManager used will depend heavily on the environment provided by the embedding program. For instance, a multiprocess Apache/mod_perl server embedding Wombat will require a SessionManager that caches sessions in shared memory, on disk or in some other location that all processes can access, whereas a multithreaded daemon embedding Wombat might use a simple memory-based SessionManager.

Server/Service/Engine/Valve

Represents a request-processing component that "wraps" around the Servlet that is ultimately responsible for processing the request. The name of a class that implements the Wombat::Valve interface MUST be specified (className="Wombat::Valve::RequestDumperValve"), as well as any attributes needed by the implementation. Many Valves may be specified for a single Container.

Valves are used to add container functionality for specific Containers, much like Filters are used to add application functionality for specific Servlets. An example of a commonly-used Valve might be a one that logs information about each request (an AccessLogValve perhaps).

Server/Service/Engine/Host

Represents a Container associated with a particular virtual host. A Host maps the request URI to a particular web application and passes the request along to the appropriate Application. The name of the host MUST be specified (name="localhost"), as well as the application base directory (appBase="webapps") which can be specified absolutely or relative to the containers home directory. Many Hosts (at least one, corresponding to the Engines default host attribute) may be specified for a single Engine.

Server/Service/Engine/Host/Alias

Represents an alternate name or names for the virtual host. For a Host named maz.org, the Alias *.maz.org might be configured to catch requests for specific hosts and subdomains in the domain. The name of the alias MUST be specified (name="*.maz.org"). Many Aliases may be specified for a particular Host.

Server/Service/Engine/Host/Logger

A Logger configured for a Host overrides any Logger configured at the Engine level.

Server/Service/Engine/Host/Realm

A Realm configured for a Host overrides any Realm configured at the Engine level.

Server/Service/Engine/Host/SessionManager

A SessionManager configured for a Host overrides any SessionManager configured at the Engine level.

Server/Service/Engine/Host/Valve

Any Valves configured for a Host add to (and execute after) any Valves configured at the Engine level.

Server/Service/Engine/Host/Application

Represents a Container associated with a particular web application. An Application inspects the request URI and passes the request along to the appropriate Servlet (as configured in the web applications deployment descriptor). The display name of the application (displayName="Examples Application") and the URI path base for the application (path="/wombat-examples") MUST be specified, as well as the webapp directory (docBase="examples") which can be specified absolutely or relative to the parent Hosts application base directory. Many Applications (at least one, corresponding to the URI path /) may be specified for a single Host.

Server/Service/Engine/Host/Application/Logger

A Logger configured for an Application overrides any Logger configured at a higher level.

Server/Service/Engine/Host/Application/Realm

A Realm configured for an Application overrides any Realm configured at a higher level.

Server/Service/Engine/Host/Application/SessionManager

A SessionManager configured for an Application overrides any SessionManager configured at a higher level.

Server/Service/Engine/Host/Application/Valve

Any Valves configured for an Application add to (and execute after) any Valves configured at a higher level.