Elvis

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com.synaptics.elvis
Class Elvis

java.lang.Object
  com.synaptics.elvis.Elvis

All Implemented Interfaces:: java.io.Serializable

public class Elvis
extends java.lang.Object
implements java.io.Serializable

Elvis is a package for implementing a singleton, not only within a JVM, but for a given user on a particular machine.

Principles of operation. The model of use for Elvis is simple. An Elvis-enabled program calls Elvis.get() with a program name and a command handler. This name is used to (hopefully) uniquely identify the Elvis-enabled program and its functions. If Elvis can establish that he is indeed the only running instance of that particular program (for that user, on that machine), he will become the One True Elvis, and establish a thread that will listen for requests from other Elvis's (also known as Elvis impersonators or Elvis clients).

Once the call to Elvis.get() returns, the program can call isTheOneTrueElvis() to determine if their Elvis is the One True Elvis. If it isn't they probably just want to send the other Elvis some messages indicating what it wants to do, and then leave the building (exit gracefully).

KNOWN SECURITY HOLES The current version of Elvis is most emphatically not secure. The most prominent holes are:

On multi-user systems (such as Linux/Unix), the Elvis information file may be created readable by users other than the creator. An attacker to could read the Elvis information file to determine the port, key, and user. This information could be used to:
- Submit bogus requests to the One True Elvis;
- Spoof responses from the One True Elvis.
- If the attacker could determine that the One True Elvis is not running, he could use this information to set up his own fraudlent Elvis.
On multi-user systems (such as Linux/Unix), the Elvis information file may be created writable by users other than the creator. An attacker to could substitute his own information in the file, and redirect requests to his own fraudulent Elvis.
In almost all cases, things that are symptomatic of an attack or probe of Elvis are simply logged, and no further actions are taken.

Right now, my use of Elvis is in a trusted environment, where these situations are considered very unlikely to occur. Although updates are planned for upcoming releases of Elvis, if you are planning to use this release of Elvis in a less secure environment, you should seriously consider beefing up Elvis's security.

Version:: $Id: Elvis.java,v 1.1 2002/05/09 07:17:17 clheiny Exp $

Nested Class Summary

private class Elvis.StatusListener
          This is used to monitor the status of the ElvisComm, and adjust the feedback string as necessary (among other possible, not yet implemented, actions.

Field Summary

private java.lang.String feedback
          A handy dandy feedback string that the Elvis application can consult.

private ElvisHandler handler
          The request handler, provided by the Elvis application

private boolean inTheBuilding
          Indicates whether this Elvis is active or not.

private ElvisComm listener
          The listener handles most of Elvis's communication.

private int port
          The port associated with this instance of Elvis

private java.lang.String program
          This is the name of the Elvis program associated with this instance of Elvis

private java.beans.PropertyChangeSupport propertyChangeSupport
          Utility field used by bound properties.

private java.beans.PropertyChangeSupport propertySupport


private boolean theOneTrueElvis
          A flag indicating whether we really are the King or not.

Constructor Summary

private Elvis(java.lang.String program, int port, ElvisHandler handler, java.beans.PropertyChangeListener propListener)
          Creates a new Elvis.

Method Summary

void addPropertyChangeListener(java.beans.PropertyChangeListener l)
          Add a PropertyChangeListener to the listener list.

static Elvis get(java.lang.String program, int port, ElvisHandler handler)
          Get an instance of the specified Elvis program on the specified port.

static Elvis get(java.lang.String program, int port, ElvisHandler handler, java.beans.PropertyChangeListener propListener)
          Get an instance of the specified Elvis program on the specified port.

java.lang.String getFeedback()
          The feedback property provides information about the state and activities of Elvis.

ElvisHandler getHandler()
          Returns the handler associated with this Elvis.

int getPort()
          Get the port number that this Elvis is (or should be) listening on.

java.lang.String getProgram()
          The program name is the unique identifier for this Elvis's functionality.

boolean hasLeftTheBuilding()
          Returns true if Elvis has left the building; false if he is still around and ready to perform.

boolean isTheOneTrueElvis()
          theOneTrueElvis indicates whether this Elvis is The King (true) or just an impersonator (false).

void leaveTheBuilding()
          Calling leaveTheBuilding() will result in the Elvis listener thread being cancelled (if this Elvis is the one true Elvis) and most Elvis related infrastructure being dismantled.

ElvisResult perform(java.lang.String data)
          Calling this will cause Elvis to do something.

void removePropertyChangeListener(java.beans.PropertyChangeListener l)
          Removes a PropertyChangeListener from the listener list.

private void setFeedback(java.lang.String feedback)
          Update the feedback string and notify any listeners.

void setHandler(ElvisHandler handler)
          Set the Handler for this Elvis.

private void setHandlerInternal(ElvisHandler handler)
          Internal worker that actually does the handler setting.

private void setPort(int port)
          setPort should only be called at class instantiation time.

private void setProgram(java.lang.String program)
          The program name can only be set internally, preferably at creation time.

private void setTheOneTrueElvis(boolean theOneTrueElvis)
          We can only set this ourselves.

Methods inherited from class java.lang.Object

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

Field Detail

propertySupport

private java.beans.PropertyChangeSupport propertySupport

theOneTrueElvis

private boolean theOneTrueElvis

A flag indicating whether we really are the King or not.

port

private int port

The port associated with this instance of Elvis

program

private java.lang.String program

This is the name of the Elvis program associated with this instance of Elvis

inTheBuilding

private boolean inTheBuilding

Indicates whether this Elvis is active or not. If Elvis has left the building, the Elvis listen thread has been cancelled, and most method invocations will throw an ElvisException.

handler

private ElvisHandler handler

The request handler, provided by the Elvis application

listener

private ElvisComm listener

The listener handles most of Elvis's communication.

feedback

private java.lang.String feedback

A handy dandy feedback string that the Elvis application can consult.

propertyChangeSupport

private java.beans.PropertyChangeSupport propertyChangeSupport

Utility field used by bound properties.

Constructor Detail

Elvis

private Elvis(java.lang.String program,
              int port,
              ElvisHandler handler,
              java.beans.PropertyChangeListener propListener)

Creates a new Elvis. This is private to force folks to use the factory method. We want them to use the factory, so we can catch attempts to create multiple Elvises on the same port.

We presume the parameters have already been vetted by the factory, and don't check them here.

Method Detail

get

public static final Elvis get(java.lang.String program,
                              int port,
                              ElvisHandler handler)

Get an instance of the specified Elvis program on the specified port. The program name may not contain the ':' or end of line characters.

If we are indeed the one true Elvis, the specified ElvisHandler will be used to handle requests.

get

public static final Elvis get(java.lang.String program,
                              int port,
                              ElvisHandler handler,
                              java.beans.PropertyChangeListener propListener)

Get an instance of the specified Elvis program on the specified port. The program name may not contain the ':' or end of line characters.

If we are indeed the one true Elvis, the specified ElvisHandler will be used to handle requests.

isTheOneTrueElvis

public boolean isTheOneTrueElvis()

theOneTrueElvis indicates whether this Elvis is The King (true) or just an impersonator (false).

If we are indeed the One True Elvis, then we will be handling all Elvis based interactions for all JVMs. The client must be ready to deal with this.

setTheOneTrueElvis

private void setTheOneTrueElvis(boolean theOneTrueElvis)

We can only set this ourselves. This will prevent someone from deciding they want to impersonate Elvis.

getPort

public int getPort()

Get the port number that this Elvis is (or should be) listening on.

getProgram

public java.lang.String getProgram()

The program name is the unique identifier for this Elvis's functionality. It is unique (hopefully) across all Elvis-capable programs in all JVMs.

This uniqueness is actually subject to the discipline exercised by the various Elvis client programmers. There is nothing in the Elvis implementation that prevents two different programmers from attempting to implement two very different Elvis programs using the name Splat. The best advice I can offer is Don't do this! Instead, try using the fully qualified (package name and class name) for the class implementing the Elvis-based functionality.

setPort

private void setPort(int port)

setPort should only be called at class instantiation time.

setProgram

private void setProgram(java.lang.String program)

The program name can only be set internally, preferably at creation time.

leaveTheBuilding

public void leaveTheBuilding()

Calling leaveTheBuilding() will result in the Elvis listener thread being cancelled (if this Elvis is the one true Elvis) and most Elvis related infrastructure being dismantled. Once Elvis has left the building, most method calls will through an ElvisException.

hasLeftTheBuilding

public boolean hasLeftTheBuilding()

Returns true if Elvis has left the building; false if he is still around and ready to perform.

getHandler

public ElvisHandler getHandler()

Returns the handler associated with this Elvis. This will be null if we are not the One True Elvis.

setHandler

public void setHandler(ElvisHandler handler)

Set the Handler for this Elvis.

setHandlerInternal

private void setHandlerInternal(ElvisHandler handler)

Internal worker that actually does the handler setting.

addPropertyChangeListener

public void addPropertyChangeListener(java.beans.PropertyChangeListener l)

Add a PropertyChangeListener to the listener list.

removePropertyChangeListener

public void removePropertyChangeListener(java.beans.PropertyChangeListener l)

Removes a PropertyChangeListener from the listener list.

getFeedback

public java.lang.String getFeedback()

The feedback property provides information about the state and activities of Elvis. For example, various stages of establishing the ports we listen to are reported.

This is not intended to be a definitive means of determining the status of Elvis. It's more intended to give useful text information that can be presented in status bars and stuff like that.

setFeedback

private void setFeedback(java.lang.String feedback)

Update the feedback string and notify any listeners.

perform

public ElvisResult perform(java.lang.String data)

Calling this will cause Elvis to do something. If we are the one true Elvis, the local ElvisHandler will be called with the specified data. If we are not the one true Elvis, the remote Elvis will be requested to perform and passed the specified data.

Overview

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Class

Use

Deprecated

Index

Home >> All >> com >> synaptics >> [ elvis overview ]

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Nested Class Summary
`private class`	`Elvis.StatusListener` This is used to monitor the status of the ElvisComm, and adjust the feedback string as necessary (among other possible, not yet implemented, actions.

Field Summary
`private java.lang.String`	`feedback` A handy dandy feedback string that the Elvis application can consult.
`private ElvisHandler`	`handler` The request handler, provided by the Elvis application
`private boolean`	`inTheBuilding` Indicates whether this Elvis is active or not.
`private ElvisComm`	`listener` The listener handles most of Elvis's communication.
`private int`	`port` The port associated with this instance of Elvis
`private java.lang.String`	`program` This is the name of the Elvis program associated with this instance of Elvis
`private java.beans.PropertyChangeSupport`	`propertyChangeSupport` Utility field used by bound properties.
`private java.beans.PropertyChangeSupport`	`propertySupport`
`private boolean`	`theOneTrueElvis` A flag indicating whether we really are the King or not.

Constructor Summary
`private`	`Elvis(java.lang.String program, int port, ElvisHandler handler, java.beans.PropertyChangeListener propListener)` Creates a new Elvis.

Method Summary
`void`	`addPropertyChangeListener(java.beans.PropertyChangeListener l)` Add a PropertyChangeListener to the listener list.
`static Elvis`	`get(java.lang.String program, int port, ElvisHandler handler)` Get an instance of the specified Elvis program on the specified port.
`static Elvis`	`get(java.lang.String program, int port, ElvisHandler handler, java.beans.PropertyChangeListener propListener)` Get an instance of the specified Elvis program on the specified port.
`java.lang.String`	`getFeedback()` The feedback property provides information about the state and activities of Elvis.
`ElvisHandler`	`getHandler()` Returns the handler associated with this Elvis.
`int`	`getPort()` Get the port number that this Elvis is (or should be) listening on.
`java.lang.String`	`getProgram()` The program name is the unique identifier for this Elvis's functionality.
`boolean`	`hasLeftTheBuilding()` Returns `true` if Elvis has left the building; `false` if he is still around and ready to perform.
`boolean`	`isTheOneTrueElvis()` `theOneTrueElvis` indicates whether this Elvis is The King (`true`) or just an impersonator (`false`).
`void`	`leaveTheBuilding()` Calling `leaveTheBuilding()` will result in the Elvis listener thread being cancelled (if this Elvis is the one true Elvis) and most Elvis related infrastructure being dismantled.
`ElvisResult`	`perform(java.lang.String data)` Calling this will cause Elvis to do something.
`void`	`removePropertyChangeListener(java.beans.PropertyChangeListener l)` Removes a PropertyChangeListener from the listener list.
`private void`	`setFeedback(java.lang.String feedback)` Update the feedback string and notify any listeners.
`void`	`setHandler(ElvisHandler handler)` Set the Handler for this Elvis.
`private void`	`setHandlerInternal(ElvisHandler handler)` Internal worker that actually does the handler setting.
`private void`	`setPort(int port)` setPort should only be called at class instantiation time.
`private void`	`setProgram(java.lang.String program)` The program name can only be set internally, preferably at creation time.
`private void`	`setTheOneTrueElvis(boolean theOneTrueElvis)` We can only set this ourselves.

com.synaptics.elvis Class Elvis

propertySupport

theOneTrueElvis

port

program

inTheBuilding

handler

listener

feedback

propertyChangeSupport

Elvis

get

get

isTheOneTrueElvis

setTheOneTrueElvis

getPort

getProgram

setPort

setProgram

leaveTheBuilding

hasLeftTheBuilding

getHandler

setHandler

setHandlerInternal

addPropertyChangeListener

removePropertyChangeListener

getFeedback

setFeedback

perform

com.synaptics.elvis
Class Elvis