Integrating Command Line Programs with Java Clients

1
Integrating Command Line Programs with Java
Clients

• Will Fisher
• PPPL Summer Intern
• Science Education Program
• August 11th, 2005

2
Motivation

• What did we want out of a command line system?
• Access the suite of command line utilities from a
  standalone application.
• Preserve the functionality and performance.
• Minimize changes to the programs.
• Editing the programs was not an option.
• Must capture their output and feed them input.
• Add graphical user interface to the command line.
• Java is a good language to use for the client
  application given its portability.
• Ultimate goal Java client ?? command line
  program.

3
Issues with Standard I/O

• Buffering
• Causes problems for reading and writing data as
  needed.
• Java API does not work well, directly, with
  terminal applications because of buffering.
• Java communication, apparently, has no such
  issues as client/servlet communication is handled
  fully and completely by the Java system.

4
PTY Implementation

• Pseudo-terminals
• Special interprocess communication channel that
  acts like a terminal.
• One end is called the master, the other end is
  called the slave.
• Data written to the master is received by the
  slave as if it were the result of a user typing
  at an ordinary terminal.
• Data written to the slave is sent to the master
  as if it were written on an ordinary terminal.
• Our use of them
• Used for communication with the command line
  program.
• Fakes a terminal device that reads from and
  writes to the command line program.
• Set terminal attributes in order to kill the
  buffering and the echoing.

5
CLTerm Technology Solution

• Forking the program
• Use the forkpty() command to fork CLTerm into two
  processes.
• The two processes are connected via a
  master-slave pseudo-terminal.
• The child process replaces its own program image
  with the image of the command line program by
  calling the subroutine execl(program).
• The new program thinks its running normally but
  is connected to a pseudo-terminal.
• The parent monitors the output and feeds input to
  the child.
• Java client ? ? CLTerm ? ? Command Line Program

6
System Architecture
User Computers
Franks Computer
Alices Computer
Bobs Computer
Java Client 1
Java Client 3
Java Applet
Java Client 2
The Network Chasm

Transpgrid PPPL Cluster
clterm
genxpl
HTTP Servlet
clterm
rplot
clterm
trxpl
clterm
rplot
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The Servlet

• Servlet complements Java applet / application
• Applet has limited sandbox on users computer
• Servlet runs on cluster http connection to
  client
• Run programs
• Access user files
• Enforce security
• Added 2 methods
• Runcl start a new clterm session
• Inputcl send a line of user input to clterm

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CLTerm.c

• How it works
• One instance of CLTerm is launched for each
  client.
• Each instance connects to one command line
  program.
• It forks a new child process which in turn
  launches the program in its place.
• They talk via a pseudo-terminal and CLTerm
  forwards the output to the servlet and feeds the
  data it gets from the servlet into the child via
  the pseudo-terminal.
• CLTerm checks each iteration of its I/O loop,
  that the child is still alive. If not then it
  sends an exit byte down the line.

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CLPanel.java

• How it works
• CLPanel inherits from JPanel and can be
  implemented in either a JFrame or a
  JInternalFrame like in ElVis.
• Has all the communication and GUI code.
• Has an I/O loop that first reads the users input
  and then looks for the programs response, sent
  via the servlet.
• If the user closes the CLPanel window, it will
  send an exit byte (ASCII code 25) down the line
  so that everything else is informed.

10
CLTerm In Action
11
Conclusion

• End result and advantages
• Successfully integrated a solution for Java
  clients to talk to command line programs.
• Minimal changes to the existing infrastructure.
• CLTerm is appropriate for larger applications
  given its encapsulated nature.
• CLPanel lets Java developers incorporate this
  panel into their own applications.
• CLPanel is a class which can be instantiated
  multiple times in the same application multiple
  windows/connections in the same app.
• Can also run as an Applet in a browser.
• Opportunity to expand PPL Fusion Grid Services.

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CLTerm Demo!