sunlabs.brazil.handler
Class DynamicConfigHandler

java.lang.Object
  sunlabs.brazil.handler.DynamicConfigHandler (view source)

All Implemented Interfaces:

Handler

public class DynamicConfigHandler
extends Object
implements Handler

The DynamicConfigHandler allows the user to change the configuration of the server and its handlers on the fly. This handler can therefore be used to swap in and out functionality, for example, by dynamically adding a new AuthHandler to add a new form of authentication to a running server.

This handler uses a special set of URLs to allow a new set of configuration properties to be uploaded. The new configuration replaces the old configuration.

The name of another Handler is supplied when this DynamicConfigHandler is initialized. This Handler is the helper or sub-handler for the DynamicConfigHandler. When the DynamicConfigHandler receives a regular HTTP request (that matches the URL prefix described below), it redirects that request to the respond method of the sub-handler.

The uploaded configuration properties are kept in a separate properties object from the server's properties. The server's properties are in fact not accessible from the sub-handler; the sub-handler can only access and/or change the properties owned by the DynamicConfigHandler.

This handler uses the following configuration properties:

handler

The name of the initial sub-handler that this DynamicConfigHandler will use to process requests. When new properties are uploaded, the sub-handler will be replaced with whatever is specified in the newly uploaded handler property.

prefix

Only URLs beginning with this string will be redirected to the sub-handler. This property belongs to the DynamicConfigHandler and is not changed when new properties are uploaded. The default is "/".

config

URLs beginning with this prefix can be used to upload or download new configuration properties to this handler, which will also dynamically change which sub-handler is installed. This property belongs to the DynamicConfigHandler and is not changed when new properties are uploaded. The default is "/config/".

Properties may be uploaded by sending them as "name=value" pairs in the body of a POST or in the "?" query parameters. The URL for uploading properties is "config/set".

The current set of properties may be retrieved from this handler by sending the URL "config/get"

A sample set of configuration parameters illustrating how to use this handler follows:

 handler=sunlabs.brazil.server.ChainHandler
 port=8081
 log=5

 handlers=dyn cgi

 dyn.class=sunlabs.brazil.server.DynamicConfigHandler
 dyn.prefix=/sparky/
 dyn.config=/config-sparky/
 dyn.handler=chain

 chain.class=sunlabs.brazil.server.ChainHandler
 chain.handlers=foo baz garply

 foo.class=sunlabs.brazil.handler.HomeDirHandler
 foo.home=/home/users/

 baz.class=sunlabs.brazil.handler.FileHandler

 garply.class=sunlabs.brazil.handler.NotFoundHandler
 garply.root="/errors/"
 garply.fileName="nofile.html"

 cgi.class = sunlabs.brazil.handler.CgiHandler
 .
 .
 .
 

These parameters set up a normal Server on port 8081, running a ChainHandler which dispatches to a DynamicConfigHandler and a CgiHandler.

The DynamicConfigHandler will listen for HTTP requests beginning with "/sparky/" and dispatch to its dynamically generated list of handlers, and listen for requests beginning with "/config-sparky/" to dynamically change that set of handlers.

To give this DynamicConfigHandler something to do, an initial set of handlers is provided with the same prefix ("dyn") as the DynamicConfigHandler itself. The prefix is stripped off those properties and the revised set of properties is passed to the DynamicConfigHandler to initialize its dynamically configurable world.

Constructor Summary

DynamicConfigHandler()

Method Summary

boolean	init(Server server, String prefix) Initializes this DynamicConfigHandler by loading the initial handler.
boolean	respond(Request request) Responds to an HTTP request by examining the "Host:" request header and dispatching to the main handler of the server that handles that virtual host.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DynamicConfigHandler

public DynamicConfigHandler()

Method Detail

init

public boolean init(Server server,
                    String prefix)

Initializes this DynamicConfigHandler by loading the initial handler. An initial handler does not need to be defined, however, since the handler configuration can be downloaded later.

Specified by:

init in interface Handler

Parameters:

server - The HTTP server that created this handler.

prefix - A prefix to prepend to all of the keys that this handler uses to extract configuration information.

Returns:

false if the initial handler was specified but could not be initialized, true otherwise.

respond

public boolean respond(Request request)
                throws IOException

Responds to an HTTP request by examining the "Host:" request header and dispatching to the main handler of the server that handles that virtual host. If the "Host:" request header was not specified, or named a virtual host that was not initialized in init from the list of virtual hosts, this method returns without handling the request.

Specified by:

respond in interface Handler

Parameters:

request - The HTTP request to be forwarded to one of the sub-servers.

Returns:

true if the sub-server handled the message, false if it did not. false is also returned if the "Host:" was unspecified or unknown.

Throws:

IOException - if there was an I/O error while sending the response to the client. Typically, in that case, the Server will (try to) send an error message to the client and then close the client's connection.

The IOException should not be used to silently ignore problems such as being unable to access some server-side resource (for example getting a FileNotFoundException due to not being able to open a file). In that case, the Handler's duty is to turn that IOException into a HTTP response indicating, in this case, that a file could not be found.