	CS 580 Client-Server Programming Fall Semester, 2000 WWW & Client-Server
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Contents of Doc 15, WWW & Client-Server

References Apache Modules http://modules.apache.org/

Servlets http://java.sun.com/products/servlet/2.2/javadoc/index.html

Tomcat http://jakarta.apache.org/

JRun http://www.allaire.com/products/jrun/index.cfm

FastCGI http://www.fastcgi.com/

The Common Gateway Interface http://hoohoo.ncsa.uiuc.edu/cgi/overview.html


Doc 15, WWW & Client-Server Slide # 2

WWW as a Client-Server System

Many people use WWW to implement client-server systems

Advantages:

WWW browsers are everywhere
People know how to use WWW
No need to distribute updates to your client
Provides links to your services

Disadvantages:

Browsers have limited functionality
http is stateless
http is slow for some applications
HTML is static


Doc 15, WWW & Client-Server Slide # 3

Generating HTML pages dynamically
WWW client-server systems need more interaction than static web pages

Dynamically generate HTML pages

Augment the functionality of browsers

Web server applications

Code/programs used to dynamically generate HTML


Doc 15, WWW & Client-Server Slide # 4

Ways to Dynamically generate HTML

Special Web servers
Special API for Web servers
Servlets
CGI
FastCGI
Active Web pages


Doc 15, WWW & Client-Server Slide # 5

Special Web Servers

Basic HTTP is not hard to implement

Write your own server to produce dynamic responses

Not common

Examples

Assignment 2
Class Wiki


Doc 15, WWW & Client-Server Slide # 6

Special API for Web servers

Web servers allow you to link code to extend their functionality

Examples

Netscape Server API (NSAPI)
Internet Server API (ISAPI) - Microsoft
Apache Modules http://modules.apache.org/
Servlets

Pros:

Fast response time

Cons

Steep learning curve
Proprietary
Language dependence
No process isolation


Doc 15, WWW & Client-Server Slide # 7

Servlets

Background
Started by Sun

Sun controls the Servlet API ( http://java.sun.com/products/servlet/2.2/javadoc/index.html)

Tomcat - Apache module that supports servlets & Java Server pages

JRun - commercial product supporting servlets & Java Server pages

What are Servlets?
Java programs that are

Run as part of a web server
Mapped to URLs

Servlet API contains 40 classes & interfaces


Doc 15, WWW & Client-Server Slide # 8

Sample Servlet Program

import java.io.*;
import java.util.Date;
import javax.servlet.*;
public class SimpleDateServlet extends GenericServlet 
   {
   public void service(ServletRequest request, 
      ServletResponse response) 
      throws ServletException, IOException
      {
      InputStream rawIn;
      DataInputStream  parsedInput;
      
      rawIn = request.getInputStream();
      parsedInput = new DataInputStream(rawIn);
      
      ServletOutputStream out = response.getOutputStream();
      
      String inputLine = parsedInput.readLine();
      if (inputLine.startsWith("date"))
         {
         Date now = new Date();
         out.println( now.toString() );
         }
      else
         out.println( "Invalid Input" );
      }
}
Doc 15, WWW & Client-Server Slide # 9

Servlet that Displays Form Data

import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class SnoopServlet extends HttpServlet 
   {
   public void doGet (HttpServletRequest request, 
      HttpServletResponse response)
      throws ServletException, IOException   
      {
      response.setContentType("text/html");
      
      ServletOutputStream out = response.getOutputStream();
      Enumeration names = request.getParameterNames();
      if (names.hasMoreElements()) 
         {
         out.println("<pre>");
         while (names.hasMoreElements()) 
            {
            String formItemName = (String)names.nextElement();
            String formItemValues[] = 
               (String []) request.getParameterValues(formItemName);
            if (formItemValues != null) 
               {
               out.print("<b> " + formItemName + " = </b>"); 
               out.println(formItemValues[0]);
               }
            out.println("<p>");
            }
         out.println("</pre>");
         }
      out.println("</body></html>");
      }
}


Doc 15, WWW & Client-Server Slide # 10

Common Gateway Interface (CGI)

Standard for calling external programs

The basic idea

Web server receives a CGI request
Web server starts the requested CGI program
Web server passes request data to CGI program
CGI program processes request
CGI program return data to Web server
Web server returns response to web client

Pros

Simplicity
Language independence
Process isolation

Cons

Start up costs for CGI program per request


Doc 15, WWW & Client-Server Slide # 11

The basic questions

How does the Web server find and run the CGI program?

How do the Web server and CGI program communicate?

What information can be sent from Web Server to the CGI program?

What information can be sent from the CGI program to the Web Server?


Doc 15, WWW & Client-Server Slide # 12

Finding and running the CGI program

Web server is configured to treat files in particular directories as programs

Often cgi-bin indicates a such a CGI directory

All files in a CGI directory and subdirectories are treated as programs

A URL that references a program in a CGI directory will cause the Web server to run that program as a CGI program

Sending a Response to the server

CGI program writes the response on the standard output

The server reads the output and forms http response

CGI defines headers for communication from CGI program to server


Doc 15, WWW & Client-Server Slide # 13

The CGI Return Headers (CGI/1.1)
The output of scripts begins with a small header. This header consists of text lines, in the same format as an HTTP header, terminated by a blank line (a line with only a linefeed or CR/LF).

Any headers that are not server directives are sent directly back to the client. Currently, this specification defines three server directives:

Content-type

This is the MIME type of the document you are returning.

Location

Returns to the server a reference to a document

If is a URL, the server will issue a redirect to the client.

If is a virtual path, the server will retrieve the document specified

Status

An HTTP/1.0 status line for the server to send to the client.


Doc 15, WWW & Client-Server Slide # 14

CGI Examples of Sending Data to a Sever

Content-type Example 1 Simple Text
File: hiMomTextPlain

Location: /net/www/www-eli/cgi-bin/cgiExamples

CGI directory: /net/www/www-eli/cgi-bin

File Contents:

   #!/bin/sh
   echo Content-type: text/plain
   echo
   echo Hi Mom,
   echo
   echo    How is Dad?
   echo I am fine.

URL:
http://www.eli.sdsu.edu/cgi-bin/cgiExamples/hiMomTextPlain

Result in Netscape when open above URL:

   Hi Mom,
   How is Dad?
   I am fine.


Doc 15, WWW & Client-Server Slide # 15

Content-type Example 1 Simple Text

Telnet Session:

   /net/www/www-eli-> telnet www.eli.sdsu.edu 80
   Trying 130.191.226.80...
   Connected to www.eli.sdsu.edu.
   Escape character is '^]'.
   GET /cgi-bin/cgiExamples/hiMomTextPlain HTTP/1.0
   HTTP/1.0 200 OK
   Server: Netscape-Commerce/1.12
   Date: Saturday, 29-Mar-97 05:04:17 GMT
   Content-type: text/plain
   Hi Mom,
   How is Dad?
   I am fine.
   Connection closed by foreign host.


Doc 15, WWW & Client-Server Slide # 16

Content-type Example 2 HTML
File: hiMomTextHtml

Location: /net/www/www-eli/cgi-bin/cgiExamples

CGI directory : /net/www/www-eli/cgi-bin

File Contents:

   #!/bin/sh
   echo Content-type: text/html
   echo
   echo Hi Mom,
   echo
   echo    How is Dad?
   echo I am fine.

URL:
http://www.eli.sdsu.edu/cgi-bin/cgiExamples/hiMomTextHtml

Result in Netscape when open above URL:

Hi Mom, How is Dad? I am fine.


Doc 15, WWW & Client-Server Slide # 17

Content-type Example 3 Some Real HTML
File: hiMomFancy

Location: /net/www/www-eli/cgi-bin/cgiExamples

CGI directory : /net/www/www-eli/cgi-bin

File Contents:

   #!/bin/sh
   echo Content-type: text/html
   echo
   echo "<B>Hi Mom</B>",
   echo
   echo    "<BIG>How is Dad?</BIG>"
   echo "<CENTER>I am fine</CENTER>".

URL:
http://www.eli.sdsu.edu/cgi-bin/cgiExamples/hiMomFancy


Doc 15, WWW & Client-Server Slide # 18

Redirection Example 1 URL
File: redirectURL

Location: /net/www/www-eli/cgi-bin/cgiExamples

CGI directory: /net/www/www-eli/cgi-bin

File Contents:

#!/bin/sh

echo Location: http://www.eli.sdsu.edu/index.html
echo
# All the stuff after this is does no good
# Client is working on the redirection

echo "<B>Hi Mom</B>",
echo
echo "<BIG>How is Dad?</BIG>"
echo "<CENTER>I am fine</CENTER>".

URL:
http://www.eli.sdsu.edu/cgi-bin/cgiExamples/redirectURL


Doc 15, WWW & Client-Server Slide # 19

Redirection Example 1 URL

Telnet Session:

   /net/www/www-eli-> telnet www.eli.sdsu.edu 80
   Trying 130.191.226.80...
   Connected to www.eli.sdsu.edu.
   Escape character is '^]'.
   GET /cgi-bin/cgiExamples/redirectURL HTTP/1.0
   HTTP/1.0 302 Found
   Server: Netscape-Commerce/1.12
   Date: Saturday, 29-Mar-97 06:25:26 GMT
   Location: http://www.eli.sdsu.edu/index.html
   <B>Hi Mom</B>,
   <BIG>How is Dad?</BIG>
   <CENTER>I am fine</CENTER>.
   Connection closed by foreign host.


Doc 15, WWW & Client-Server Slide # 20

Redirection Example 2 Path
File: redirectPath

Location: /net/www/www-eli/cgi-bin/cgiExamples

CGI directory : /net/www/www-eli/cgi-bin

File Contents:

   #!/bin/sh
   echo Location: /cgi-bin/cgiExamples/hiMomFancy
   echo

URL:
http://www.eli.sdsu.edu/cgi-bin/cgiExamples/redirectPath


Doc 15, WWW & Client-Server Slide # 21

Redirection Example 2 Path
Telnet Session:

   /net/www/www-eli-> telnet www.eli.sdsu.edu 80
   Trying 130.191.226.80...
   Connected to www.eli.sdsu.edu.
   Escape character is '^]'.
   GET /cgi-bin/cgiExamples/redirectPath HTTP/1.0
   HTTP/1.0 200 OK
   Server: Netscape-Commerce/1.12
   Date: Saturday, 29-Mar-97 06:38:56 GMT
   Content-type: text/html
   <B>Hi Mom</B>,
   <BIG>How is Dad?</BIG>
   <CENTER>I am fine</CENTER>.
   Connection closed by foreign host.


Doc 15, WWW & Client-Server Slide # 22

Status Example 1
File: status

Location: /net/www/www-eli/cgi-bin/cgiExamples

CGI directory : /net/www/www-eli/cgi-bin

File Contents:

   #!/bin/sh
   echo Content-type: text/plain
   echo Status: 298 Okey Dokey with Me
   echo
   echo Hi Mom,
   echo
   echo    How is Dad?
   echo I am fine.

URL:
http://www.eli.sdsu.edu/cgi-bin/cgiExamples/status


Doc 15, WWW & Client-Server Slide # 23

Status Example 1
Telnet Session:

   /net/www/www-eli -> telnet www.eli.sdsu.edu 80
   Trying 130.191.226.80...
   Connected to www.eli.sdsu.edu.
   Escape character is '^]'.
   GET /cgi-bin/cgiExamples/status HTTP/1.0
   HTTP/1.0 298 Okey Dokey with Me
   Server: Netscape-Commerce/1.12
   Date: Saturday, 29-Mar-97 19:49:50 GMT
   Content-type: text/plain
   Hi Mom,
   How is Dad?
   I am fine.
   Connection closed by foreign host.


Doc 15, WWW & Client-Server Slide # 24

Information from the Web server to the CGI Program

Web server sends data to the CGI Program via:

Environment variables
Command line
Standard input

Environment Variables

AUTH_TYPE	CONTENT_LENGTH	CONTENT_TYPE
DOCUMENT_ROOT	GATEWAY_INTERFACE	HTTP_ACCEPT
HTTP_USER_AGENT	PATH_INFO	PATH_TRANSLATED
QUERY_STRING	REMOTE_ADDR	REMOTE_HOST
REMOTE_IDENT	REMOTE_USER	REQUEST_METHOD
SCRIPT_NAME	SERVER_NAME	SERVER_PORT
SERVER_PROTOCOL	SERVER_SOFTWARE

Not all variables are set for each request

See http://hoohoo.ncsa.uiuc.edu/cgi/env.html for more information.


Doc 15, WWW & Client-Server Slide # 25

Example of CGI Environment Variables

File: variables

Location: /net/www/www-eli/cgi-bin/cgiExamples

URL:
http://www.eli.sdsu.edu/cgi-bin/cgiExamples/variables

File Contents:

   #!/bin/sh
   # Code from http://hoohoo.ncsa.uiuc.edu/cgi/test-cgi.txt
   echo Content-type: text/plain
   echo
   echo CGI/1.0 test script report:
   echo
   echo argc is $#. argv is "$*".
   echo
   echo CONTENT_LENGTH = $CONTENT_LE
   echo CONTENT_TYPE = $CONTENT_TYPE
   echo GATEWAY_INTERFACE = $GATEWAY_INTERFACE
   echo HTTP_ACCEPT = "$HTTP_ACCEPT"
   echo PATH_INFO = $PATH_INFO
   echo PATH_TRANSLATED = $PATH_TRANSLATED
   echo QUERY_STRING = $QUERY_STRING
   echo REMOTE_ADDR = $REMOTE_ADDR
   echo REMOTE_HOST = $REMOTE_HOST
   echo REMOTE_USER = $REMOTE_USER
   echo REQUEST_METHOD = $REQUEST_METHOD
   echo SCRIPT_NAME = $SCRIPT_NAME
   echo SERVER_NAME = $SERVER_NAME
   echo SERVER_PORT = $SERVER_PORT
   echo SERVER_PROTOCOL = $SERVER_PROTOCOL
   echo SERVER_SOFTWARE = $SERVER_SOFTWARE


Doc 15, WWW & Client-Server Slide # 26

Other Data sent to the CGI Program
The following http request methods can be used to send other data to the CGI program:

GET
POST
PUT
ISINDEX query

GET
GET sends data via the QUERY_STRING environment variable

GET data is sent in one of two ways:

Via a html form
By placing name-value pairs at the end of a URL

The data is encoded in x-www-form-urlencoded format when send via html form

A space is encoded as a '+"

All characters other than a-z, A-Z, 0-9, '_' and space are encoded as a % followed by two hex digits that make up the character.


Doc 15, WWW & Client-Server Slide # 27

GET Method Example 1. URL

URL:
http://www.eli.sdsu.edu/cgi-bin/cgiExamples/variables?name=Roger&class=596

Result in Netscape when open above URL:

   (I removed some variables to save space)
   CGI/1.0 test script report:
   CONTENT_LENGTH =
   CONTENT_TYPE =
   QUERY_STRING = name=Roger&class=cs596
   REQUEST_METHOD = GET
   SCRIPT_NAME = /cgi-bin/cgiExamples/variables
   SERVER_PORT = 80
   SERVER_PROTOCOL = HTTP/1.0
   SERVER_SOFTWARE = Netscape-Commerce/1.12


Doc 15, WWW & Client-Server Slide # 28

GET Method Example 2. URL bad form

URL:
http://www.eli.sdsu.edu/cgi-bin/cgiExamples/variables?name<Roger;class@cs596

Result in Netscape when open above URL:

CGI/1.0 test script report:
argc is 1. argv is name\<Roger\;class@cs596.
CONTENT_LENGTH =
CONTENT_TYPE =
GATEWAY_INTERFACE = CGI/1.1
HTTP_ACCEPT = image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, image/png, */*
PATH_INFO =
PATH_TRANSLATED =
QUERY_STRING = name<Roger;class@cs596
REMOTE_ADDR = 24.177.53.118
REMOTE_HOST =
REMOTE_USER =
REQUEST_METHOD = GET
SCRIPT_NAME = /cgi-bin/cgiExamples/variables
SERVER_NAME = www.eli.sdsu.edu
SERVER_PORT = 80
SERVER_PROTOCOL = HTTP/1.0
SERVER_SOFTWARE = Apache/1.3.9 (Unix) PHP/3.0.12
Doc 15, WWW & Client-Server Slide # 29

GET Method Example 3. A Form

The Form, HTML

   <P>
   <FORM ACTION=
   "http://www.eli.sdsu.edu/cgi-bin/cgiExamples/variables"
   METHOD="GET">
   <INPUT TYPE="checkbox" NAME="top" VALUE="on">
   <INPUT TYPE="checkbox" NAME="left" VALUE="on">
   <INPUT TYPE="submit" VALUE="Submit"> <P>
   </FORM>

The Form, Rendered

<FORM METHOD="GET" ACTION="http://www.eli.sdsu.edu/cgi-bin/cgiExamples/variables">
<INPUT TYPE="CHECKBOX" NAME="top" VALUE="on">
<INPUT TYPE="CHECKBOX" NAME="left" VALUE="on">
<INPUT TYPE="SUBMIT" VALUE="Submit">
</FORM>

Result in Netscape upon submit, both boxes checked:

   CGI/1.0 test script report:
   argc is 0. argv is .
   CONTENT_LENGTH =
   GATEWAY_INTERFACE = CGI/1.1
   REQUEST_METHOD = GET
   QUERY_STRING = top=on&left=on


Doc 15, WWW & Client-Server Slide # 30

POST and PUT
When data is sent via POST or PUT,

the CONTENT_LENGTH environment variable contains the number of bytes of data sent to the CGI program via the standard input

POST Method Example 1. A Form
The Form, HTML

   <P>
   <FORM ACTION=
   "http://www.eli.sdsu.edu/cgi-bin/cgiExamples/variables"
   METHOD="POST">
   <INPUT TYPE="checkbox" NAME="top" VALUE="on">
   <INPUT TYPE="checkbox" NAME="left" VALUE="on">
   <INPUT TYPE="submit" VALUE="Submit"> <P>
   </FORM>

The Form, Rendered
<FORM METHOD="POST" ACTION="http://www.eli.sdsu.edu/cgi-bin/cgiExamples/variables">
<INPUT TYPE="CHECKBOX" NAME="top" VALUE="on">
<INPUT TYPE="CHECKBOX" NAME="left" VALUE="on">
<INPUT TYPE="SUBMIT" VALUE="Submit">
</FORM>


Doc 15, WWW & Client-Server Slide # 31

Result in Netscape upon submit, both boxes checked:

   CGI/1.0 test script report:
   argc is 0. argv is .
   CONTENT_LENGTH =
   CONTENT_TYPE = application/x-www-form-urlencoded
   GATEWAY_INTERFACE = CGI/1.1
   HTTP_ACCEPT = image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, */*
   PATH_INFO =
   PATH_TRANSLATED =
   QUERY_STRING =
   REMOTE_ADDR = 130.191.4.123
   REMOTE_HOST = ebbsrv1p22.sdsu.edu
   REMOTE_USER =
   REQUEST_METHOD = POST
   SCRIPT_NAME = /cgi-bin/cgiExamples/variables
   SERVER_NAME = www.eli.sdsu.edu
   SERVER_PORT = 80
   SERVER_PROTOCOL = HTTP/1.0
   SERVER_SOFTWARE = Netscape-Commerce/1.12


Doc 15, WWW & Client-Server Slide # 32

CGI & Java

Problems using Java program as CGI

Java can not read environment variables

CGI requires access to environment variables

Java programs are started with a two word command:

"java ClassName"
All methods of calling CGI programs (in Unix) only allow a one-word command to start the program

Java uses the CLASSPATH environment variable to find classes

The web server, not you, runs your CGI programs.
Your CGI programs do not use your environment

Problems with Java & CGI on rohan

CGI programs on rohan do not have write permission on rohan


Doc 15, WWW & Client-Server Slide # 33

Solution to Java & CGI problems
Use a wrapper program

A sample CGI Java program

class HiMom {
   public static void main(String args[]) {
   System.out.print("Content-type: text/plain\n\n");
   System.out.println("Hi Mom");
   }  
}

A simple wrapper for Hi Mom

#!/bin/sh
JAVA="/opt/java/bin/java"
$JAVA  HiMom

Make the URL request refer to the wrapper program

See http://www-rohan.sdsu.edu/faculty/vinge/courses/spring00/cs580/notes/cgiJava/cgiJava.html for a complete solution

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2000 SDSU & Roger Whitney, 5500 Campanile Drive, San Diego, CA 92182-7700 USA.
OpenContent license defines the copyright on this document.

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