[[FastCGI]]

Integrating FastCGI with Java

Steve Harris
Open Market, Inc.
7 May 1996

Copyright © 1996 Open Market, Inc. 245 First Street, Cambridge, MA 02142 U.S.A.
Tel: 617-621-9500 Fax: 617-621-1703 URL: http://www.openmarket.com/

1. Introduction

Java is an object-oriented programming language developed by Sun Microsystems. The Java Depvelopers Kit (JDK), which contains the basic Java class packages, is available from Sun in both source and binary forms at Sun's JavaSoft site. This document assumes that you have some familiarity with the basics of compiling and running Java programs.

There are two kinds of applications built using Java.

The initial emphasis on using Java for client side applets should not obscure the fact that Java is a full strength programming language which can be used to develop server side stand alone applications, including CGI and now FastCGI applications.

The remainder of this document explains how to write and run FastCGI Java applications. It also illustrates the conversion of a sample Java CGI program to a FastCGI program.

2. Writing FastCGI applications in Java

Writing a FastCGI application in Java is as simple as writing one in C.
  1. Import the FCGIInterface class.
  2. Perform one-time initialization at the top of the main() method.
  3. Create a new FCGIInterface object and send it an FCGIaccept() message in a loop.
  4. Put the per-request application code inside that loop.
On return from FCGIaccept() you can access the request's environment variables using System.getProperty and perform request-related I/O through the standard variables System.in, System.out, and System.err.

To illustrate these points, the kit includes examples/TinyCGI, a CGI Java application, and examples/TinyFCGI, the FastCGI version of TinyCGI. These programs perform the same functions as the C programs examples/tiny-cgi.c and examples/tiny-fcgi.c that are used as examples in the FastCGI Developer's Kit document.

A. TinyCGI

 
class TinyCGI {	
	public static void main (String args[]) {		
		int count = 0;
                ++count;
		System.out.println("Content-type: text/html\n\n");
		System.out.println("<html>");
		System.out.println(
	                "<head><TITLE>CGI Hello</TITLE></head>");
		System.out.println("<body>");
		System.out.println("<H3>CGI-Hello</H3>");
		System.out.println("request number " + count + 
					" running on host " 
				+ System.getProperty<"SERVER_NAME"));
		System.out.println("</body>");
		System.out.println("</html>"); 
		}
	}

B. TinyFCGI

 
import FCGIInterface;

class TinyFCGI {	
	public static void main (String args[]) {		
		int count = 0;
 		while(new FCGIInterface().FCGIaccept()>= 0) {
			count ++;
			System.out.println("Content-type: text/html\n\n");
			System.out.println("<html>");
			System.out.println(
			  "<head><TITLE>FastCGI-Hello Java stdio</TITLE></head>");
			System.out.println("<body>");
			System.out.println("<H3>FastCGI-HelloJava stdio</H3>");
			System.out.println("request number " + count + 
					" running on host " 
				+ System.getProperty<"SERVER_NAME"));
			System.out.println("</body>");
			System.out.println("</html>"); 
			}
		}
	}

C. Running these Examples

We assume that you have downloaded the JDK and the FastCGI Developer's Kit, and that you have a Web server running that can access the fcgi-devel-kit/examples directory. In all cases where we specify paths, we are using relative paths within fcgi-devel-kit or the JDK which will need to be enlarged to a full path by the user.
Configuring
  1. Add your JDK's java/bin directory to your Unix PATH if it isn't there already.

  2. Add the directories fcgi-devel-kit/examples and fcgi-devel-kit/java/classes to your Java CLASSPATH.

  3. In your Open Market Secure WebServer configuration file, httpd.config, add the following two lines:

    ExternalAppClass TinyFCGI -host hostName:portNum
    Responder TinyFCGI fcgi-devel-kit/examples/TinyFCGI


    On other servers you can use cgi-fcgi to get a similar effect.
  4. Create a soft link examples/javexe to the java/bin directory in your JDK. This link is required only to run the CGI scripts examples/TinyCGI.cgi and examples/TinyFCGI.cgi, which use it to invoke the Java interpreter java/bin/java. It is not used by FastCGI applications.
Running

Due to gaps in the Java interpreter's support for listening sockets, Java FastCGI applications are currently limited to being started as external applications. They can't be started and managed by the Web server because they are incapable of using a listening socket that the Web server creates.

3. Standard I/O and Application Libraries

As we have seen above, FastCGI for Java offers a redefinition of standard I/O corresponding to the the fcgi_stdio functionality. It also offers a set of directly callable I/O methods corresponding to the fcgiapp C library. To understand where these methods occur we need to look briefly at the FastCGI redefinition of standard I/O.

Java defines standard I/O in the java.System class as follows:

public static InputStream in = new BufferedInputStream(new FileInputStream(FileDescriptor.in), 128);
public static PrintStream out = new PrintStream(new BufferedOutputStream(new FileOutputStream(FileDescriptor.out), 128), true);
public static PrintStream err = new PrintStream(new BufferedOutputStream(new FileOutputStream(FileDescriptor.err), 128), true);

The File Descriptors in, out, err are constants set to 0, 1 and 2 respectively.

The FastCGI interface redefines java.System in, out, and err by replacing the File streams with Socket streams and inserting streams which know how to manage the FastCGI protocol between the Socket streams and the Buffered streams in the above definitions.

For those cases where the FCGI application needs to bypass the standard I/O streams, it can directly access the methods of the FCGI input and output streams which roughly correspond to the functions in the C fcgiapp library. These streams can be accessed via the request class variable in FCGIInterface. Each Request object has instance variables that refer to an FCGIInputStream, and to two FCGIOutputStreams associated with that request.

4. Environment Variables

Java does not use the C environ list. Nor is there a getenv command that reads system environment variables. This is intentional for reasons of portability and security. Java has an internal dictionary of properties which belongs to the System class. These System properties are name/value associations that constitute the Java environment. When a Java application starts up, it reads in a file with default properties. As we have seen, additional System properties may be inserted by using the -D Java command argument.

For CGI, where the Java application is invoked from a .cgi script that, in turn, invokes the Java interpreter, this script could read the environment and pass the variables to the Java application either by writing a file or by creating -D options on the fly. Both of these methods are somewhat awkward.

For FastCGI Java applications, the environment variables are obtained from the FastCGI web server via FCGI_PARAMS records that are sent to the application at the start of each request. The FastCGI interface stores the original startup properties, combines these with the properties obtained from the server, and puts the new set of properties in the System properties dictionary. The only parameter that has to be specifically added at startup time is the FCGI_PORT parameter for the Socket creation. In the future, we expect that even this parameter won't be needed, since its use is due to an acknowledged rigidity in the JDK's implementation of sockets.

5. Further examples: EchoFCGI and Echo2FCGI

The next two examples illustrate the points made in the last two sections. EchoFCGI and Echo2FCGI both echo user input and display the application's environment variables. EchoFCGI reads the user input from System.in, while Echo2FCGI reads the user input directly from the intermediate FastCGI input stream.

A. EchoFCGI

import FCGIInterface;
import FCGIGlobalDefs;
import java.io.*;

class EchoFCGI {
	
	public static void main (String args[]) {
		int status = 0;
 		while(new FCGIInterface().FCGIaccept()>= 0) {
		System.out.println("Content-type: text/html\n\n");
			System.out.println("<html>");
			System.out.println(
				"<head%gt;<TITLE>FastCGI echo
                                      </TITLE></head>");
			System.out.println("<body>");	
			System.out.println(
                                         "<H2>FastCGI echo</H2>");
			System.out.println("<H3>STDIN</H3>");
			for ( int c = 0; c != -1; ) {
				try {
					c = System.in.read();
				} catch(IOException e) {
					System.out.println(
					"<br><b>SYSTEM EXCEPTION");
					Runtime rt = Runtime.getRuntime();
					rt.exit(status);
					}
				if (c != -1) {	
					System.out.print((char)c);
					}
				}
			System.out.println(
				"<H3>Environment Variables:</H3>");
	
			System.getProperties().list(System.out);
			System.out.println("</body>");
			System.out.println("</html>");
	   		}
		}
  	}

B. Echo2FCGI

import FCGIInterface;
import FCGIGlobalDefs;
import FCGIInputStream;
import FCGIOutputStream;
import FCGIMessage;
import FCGIRequest;
import java.io.*;

class Echo2FCGI {

	public static void main (String args[]) {
		int status = 0;
                FCGIInterface intf = new FCGIInterface();
 		while(intf.FCGIaccept()>= 0) {
		System.out.println("Content-type: text/html\n\n");
			System.out.println("<html>");
			System.out.println(
				"<head><TITLE>FastCGI echo
                                    </TITLE></head>");
			System.out.println("<body>");			
			System.out.println("<H2>FastCGI echo</H2>");
			System.out.println("<H3>STDIN:</H3">);
			for ( int c = 0; c != -1; ) {
				try {
					c = intf.request.inStream.read();
				} catch(IOException e) {
					System.out.println(
					"<br><b>SYSTEM EXCEPTION");
					Runtime rt = Runtime.getRuntime();
					rt.exit(status);
					}
				if (c != -1) {	
					System.out.print((char)c);
					}
				}
			System.out.println(
				"<H3>Environment Variables:</H3>");
	
			System.getProperties().list(System.out);
			System.out.println(<"/body>");
			System.out.println("</html>");
	   		}
		}
  	}

C. Running these Examples

Configuring
As with TinyFCGI, you need to configure the web server to recognize these two FastCGI applications. Your configuration now looks like this:

ExternalAppClass java1 -host hostname:portNum
Responder java1 fcgi-devel-kit/examples/TinyFCGI
ExternalAppClass java2 -host hostname:portNumA
Responder java2 fcgi-devel-kit/examples/EchoFCGI
ExternalAppClass java3 -host hostname:porNumB
Responder java3 fcgi-devel-kit/examples/Echo2FCGI

Note that the application classes and port numbers are different for each application.

Running
As with TinyFCGI, you need to run these programs with the -D option using FCGI_PORT and the appropriate port number. To get some data for standard input we have created two html pages with forms that use a POST method. These are echo.html and echo2.html. You must edit these .html files to expand the path to fcgi-devel-kit/examples to a full path. Once the appropriate Java program is running, point your browser at the corresponding HTML page, enter some data and select the go_find button.

6. FastCGI Java Classes

The Java FastCGI classes are included in both source and byte code format in fcgi-devel-kit/java/src and :fcgi-devel-kit/java/classes respectively. The following is a brief description of these classes:

FCGIInterface
This class contains the FCGIaccept method called by the FastCGI user application. This method sets up the appropriate FastCGI environment for communication with the web server and manages FastCGI requests.
FCGIInputStream
This input stream manages FastCGI internal buffers to ensure that the user gets all of the FastCGI messages associated with a request. It uses FCGIMessage objects to interpret these incoming messages.
FCGIOutputStream
This output stream manages FastCGI internal buffers to send user data back to the web server and to notify the server of various FCGI protocol conditions. It uses FCGIMessage objects to format outgoing FastCGI messages.
FCGIMessage
This is the only class that understands the actual structure of the FastCGI messages. It interprets incoming FastCGI records and constructs outgoing ones..
FCGIRequest
This class currently contains data fields used by FastCGI to manage user requests. In a multi-threaded version of FastCGI, the role of this class will be expanded.
FCGIGlobalDefs
This class contains definitions of FastCGI constants.

Steve Harris // harris@openmarket.com