Wombat - a Perl servlet container
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.
Web application directories are generally located beneath a single
application base directory which in turn is usually located beneath
the container's 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 container's
home directory. As well, each Application configured in the container
has the option of locating its webapp directory outside its Host's
application base directory.
A typical directory structure for Wombat embedded within
Apache/mod_perl might be:
# container's home dir
/usr/local/apache
# default hosts's appbase dir
/usr/local/apache/webapps
# examples app's webapp dir
/usr/local/apache/webapps/examples
# another host's appbase dir
/home/bcm/maz.org/webapps
# another app's webapp dir
/home/bcm/maz.org/webapps/comics
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
application's 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 container's home directory. Many Hosts
(at least one, corresponding to the Engine's 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
application's 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 Host's
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.
Each web application's resources (images, static HTML files, templates
and classes) are located in a single webapp directory. This makes
it trivially easy to organize and deploy individual web applications.
Each webapp directory MUST contain a directory named
WEB-INF. This directory MUST contain the web application
deployment descriptor, web.xml (see WEB APPLICATION CONFIGURATION). Additionally it MAY contain a lib directory in
which application-specific modules are located. If the lib
directory exists, it will be added to @INC when the application is
loaded so that application classes are visible.
All contents of the webapp directory EXCEPT the WEB-INF
directory and everything beneath it will be visible at the path
specified for the Application in the container's deployment descriptor
(see CONTAINER CONFIGURATION). For example, if an application's
path is configured as ``/wombat-examples'', then the file named
index.html located inside the webapp directory would be visible at
the URI ``/wombat-examples/index.html''. The context-relative path of
the file would be ``/index.html''.
The behavior and attributes of a particular web application are
controlled by a web application deployment descriptor (web.xml)
as specified in the Java (TM) servlet specification. The elements that
may be included in web.xml are defined in the servlet specification
and in the DTD included in the libservlet distribution.
Web application deployment descriptor elements recognized by Wombat:
- web-app
-
- web-app/context-param
-
- web-app/context-param/param-name
-
- web-app/context-param/param-value
-
- web-app/display-name
-
- web-app/login-config
-
- web-app/login-config/auth-method
-
- web-app/login-config/realm-name
-
- web-app/security-constraint
-
- web-app/security-constraint/auth-constraint
-
- web-app/security-constraint/auth-constraint/role-name
-
- web-app/security-constraint/display-name
-
- web-app/security-constraint/user-data-constraint
-
- web-app/security-constraint/user-data-constraint/transport-guarantee
-
- web-app/security-constraint/web-resource-collection
-
- web-app/security-constraint/web-resource-collection/http-method
-
- web-app/security-constraint/web-resource-collection/url-pattern
-
- web-app/security-constraint/web-resource-collection/web-resource-name
-
- web-app/servlet
-
- web-app/servlet/init-param
-
- web-app/servlet/init-param/param-name
-
- web-app/servlet/init-param/param-value
-
- web-app/servlet/security-role-ref
-
- web-app/servlet/security-role-ref/role-name
-
- web-app/servlet/security-role-ref/role-link
-
- web-app/servlet/servlet-class
-
- web-app/servlet/servlet-name
-
- web-app/servlet-mapping
-
- web-app/servlet-mapping/url-pattern
-
- web-app/servlet-mapping/servlet-name
-
- web-app/session-config
-
- web-app/session-timeout
-
Elements currently not recognized by Wombat, or for which Wombat does
not currently provide feature support:
- web-app/context-param/description
-
- web-app/description
-
- web-app/distributable
-
- web-app/ejb-local-ref/description
-
- web-app/ejb-local-ref/ejb-ref-name
-
- web-app/ejb-local-ref/ejb-ref-type
-
- web-app/ejb-local-ref/local-home
-
- web-app/ejb-local-ref/local
-
- web-app/ejb-local-ref/ejb-link
-
- web-app/ejb-ref/description
-
- web-app/ejb-ref/ejb-ref-name
-
- web-app/ejb-ref/ejb-ref-type
-
- web-app/ejb-ref/home
-
- web-app/ejb-ref/remote
-
- web-app/ejb-ref/ejb-link
-
- web-app/env-entry
-
- web-app/env-entry/description
-
- web-app/env-entry/env-entry-name
-
- web-app/env-entry/env-entry-value
-
- web-app/env-entry/env-entry-type
-
- web-app/error-page
-
- web-app/error-page/error-code
-
- web-app/error-page/exception-type
-
- web-app/error-page/location
-
- web-app/filter
-
- web-app/filter/icon
-
- web-app/filter/icon/small-icon
-
- web-app/filter/icon/large-icon
-
- web-app/filter/init-param
-
- web-app/filter/init-param/param-name
-
- web-app/filter/init-param/param-value
-
- web-app/filter/filter-name
-
- web-app/filter/display-name
-
- web-app/filter/description
-
- web-app/filter/filter-class
-
- web-app/filter/init-param
-
- web-app/filter-mapping
-
- web-app/filter-mapping/filter-name
-
- web-app/filter-mapping/url-pattern
-
- web-app/filter-mapping/servlet-name
-
- web-app/icon
-
- web-app/icon/small-icon
-
- web-app/icon/large-icon
-
- web-app/listener
-
- web-app/listener-class
-
- web-app/login-config/form-login-config
-
- web-app/login-config/form-login-config/form-login-page
-
- web-app/login-config/form-login-config/form-error-page
-
- web-app/mime-mapping
-
- web-app/mime-mapping/extension
-
- web-app/mime-mapping/mime-type
-
- web-app/resource-env-ref
-
- web-app/resource-env-ref/description
-
- web-app/resource-env-ref/resource-env-ref-name
-
- web-app/resource-env-ref/resource-env-ref-type
-
- web-app/resource-ref
-
- web-app/resource-ref/description
-
- web-app/resource-ref/res-auth
-
- web-app/resource-ref/res-ref-name
-
- web-app/resource-ref/res-sharing-scope
-
- web-app/resource-ref/res-type
-
- web-app/security-constraint/auth-constraint/description
-
- web-app/security-constraint/user-data-constraint/description
-
- web-app/security-constraint/web-resource-collection/description
-
- web-app/security-role
-
- web-app/security-role/description
-
- web-app/security-role/role-name
-
- web-app/servlet/description
-
- web-app/servlet/display-name
-
- web-app/servlet/icon
-
- web-app/servlet/icon/small-icon
-
- web-app/servlet/icon/large-icon
-
- web-app/servlet/jsp-file
-
- web-app/servlet/load-on-startup
-
- web-app/servlet/run-as/description
-
- web-app/servlet/run-as/role-name
-
- web-app/servlet/security-role-ref/description
-
- web-app/taglib
-
- web-app/taglib/taglib-uri
-
- web-app/taglib/taglib-location
-
- web-app/welcome-file-list
-
- web-app/welcome-file-list/welcome-file
-
Wombat will eventually implement the entire Java (TM) servlet
specification as adapted to Perl by libservlet. Currently it
supports just enough to be classified as a 'proof of concept' servlet
container.
Features currently not supported by Wombat but likely to be supported
in the near future include:
- Application class reloading (SRV.3.7)
-
- Application replacing (SRV.9.8)
-
- Application events (SRV.10)
-
- Auth methods: client cert, digest, form (SRV.12.5)
-
- Compartmentalized class loading (SRV.9.7.2)
-
- Secure connector redirection
-
- Clustering/session distribution (SRV.2.2, SRV.3.4.1, SRV.7.7.2,
SRV.10.6)
-
- Environment entries (SRV.9.11)
-
- Environment/external resources (SRV.9.11)
-
- Error handling request attributes and pages (SRV.9.9)
-
- Filtering (SRV.6)
-
- Internationalization (SRV.4.8, SRV.4.9, SRV.5.4)
-
- MIME mappings
-
- Multiple protocol support
-
- Named request dispatchers (SRV.8.2)
-
- Request dispatcher attributes (SRV.8.3, SRV.8.4)
-
- Request path translation (SRV.4.5)
-
- Security roles (SRV.12.3)
-
- Servlet context resources (SRV.3.5)
-
- Servlet context working directories (SRV.3.7.1)
-
- Servlet load-on-startup (SRV.2.3.1)
-
- Session tracking via SSL or URL rewriting (SRV.7.1)
-
- Session events (SRV.7.4, SRV.7.5, SRV.10.7)
-
- SSL attributes (SRV.4.7)
-
- Welcome files (SRV.9.10)
-
Features not likely to ever be supported include:
- EJB
-
- Icons
-
- JSP files
-
- Taglibs
-
No consideration has been given to threading. When the threading
environment in perl has settled down, this may change.
Apache::Wombat,
mod_perl,
Servlet
Java (TM) Servlet 2.3 Specification:
http://www.jcp.org/aboutJava/communityprocess/final/jsr053/
Brian Moseley, bcm@maz.org
Largely inspired by Tomcat, the Apache Java (TM) servlet container at
http://jakarta.apache.org/tomcat/. Many thanks!