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 it’s 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 Bob’s Computer Alice’s Computer Frank’s Computer Java Client 1 Java Client 3 Java Applet Java Client 2 The Network Chasm Transpgrid — PPPL Cluster HTTP Servlet clterm genxpl clterm rplot clterm trxpl clterm rplot

7. The Servlet • Servlet complements Java applet / application • Applet has limited “sandbox” on user’s 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

8. 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.

9. 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 user’s input and then looks for the program’s 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.

12. CLTerm Demo!