CS 596: Client-Server Programming
Spring Semester, 1997
Doc 18, CGI

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San Diego State University -- This page last updated Apr 1, 1997

Contents of Doc 18, CGI

References

Common Gateway Interface (CGI)	slide # 1
...How does the Web server find and run the CGI program	slide # 2
...How does the CGI program send Responses to the server	slide # 2
......The CGI Return Headers (CGI/1.1)	slide # 3
......Content-type	slide # 4
.........Example 1 Simple Text	slide # 4
.........Example 2 HTML	slide # 6
.........Example 3 Some Real HTML	slide # 8
......Redirection	slide # 9
.........Example 1 URL	slide # 9
.........Example 2 Path	slide # 11
......Status	slide # 13
.........Example 1	slide # 13
...Information from the Web server to the CGI Program	slide # 15
......Environment Variables	slide # 15
......GET method	slide # 18
......POST and PUT	slide # 21

Doc 18, CGI Slide # 1

References

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

Doc 18, CGI Slide # 2

CGI, WWW, and Client Server

Common Gateway Interface (CGI)

The basic idea

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 18, CGI Slide # 3

How does the Web server find and

run 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

How does the CGI program send Responses to the server?

CGI program writes all responses to the server on the standard output

CGI program output requires headers

Doc 18, CGI Slide # 4

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 which 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

This is used to specify to the server that you are returning a reference to a document rather than an actual document.

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

If the argument to this is a virtual path, the server will retrieve the document specified as if the client had requested that document originally. ? directives will work in here, but # directives must be redirected back to the client.

Status

This is used to give the server an HTTP/1.0 status line to send to the client. The format is nnn xxxxx, where nnn is the 3-digit status code, and xxxxx is the reason string, such as "Forbidden".

Doc 18, CGI Slide # 5

Content-type Example 1 Simple Text

File: hiMomTextPlain

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

Top level: 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 18, CGI Slide # 6
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 18, CGI Slide # 7

Content-type Example 2 HTML

File: hiMomTextHtml

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

Top level: 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 18, CGI Slide # 8

Content-type Example 2 HTML

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/hiMomTextHtml HTTP/1.0

HTTP/1.0 200 OK
Server: Netscape-Commerce/1.12
Date: Saturday, 29-Mar-97 05:18:01 GMT
Content-type: text/html

Hi Mom,

How is Dad?
I am fine.
Connection closed by foreign host.

What's the difference?

Doc 18, CGI Slide # 9

Content-type Example 3 Some Real HTML

File: hiMomFancy

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

Top level: 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

Result in Netscape when open above URL:


Hi Mom, How is Dad? 
                                         I am fine

Doc 18, CGI Slide # 10

Redirection Example 1 URL

File: redirectURL

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

Top level: 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

Result in Netscape when open above URL:

You see my home page

Doc 18, CGI Slide # 11

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 18, CGI Slide # 12

Redirection Example 2 Path

File: redirectPath

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

Top level: 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

Result in Netscape when open above URL:


Hi Mom, How is Dad? 
                                         I am fine

Doc 18, CGI Slide # 13

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 18, CGI Slide # 14

Status Example 1

File: status

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

Top level: 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

Result in Netscape when open above URL:


Hi Mom,

How is Dad?
I am fine.

Doc 18, CGI Slide # 15
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 18, CGI Slide # 16

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

Some environment variables that are sent under a range of conditiions, not all are sent for each request

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

See http://hoohoo.ncsa.uiuc.edu/cgi/env.html for the official word on these.

Doc 18, CGI Slide # 17

Example of Env. Varaiables sent to CGI Program

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 18, CGI Slide # 18
Result in Netscape when open above URL:

CGI/1.0 test script report:

argc is 0. argv is .

CONTENT_LENGTH =
CONTENT_TYPE =
GATEWAY_INTERFACE = CGI/1.1
HTTP_ACCEPT = image/gif, image/x-xbitmap, image/jpeg,
image/pjpeg, */*
PATH_INFO =
PATH_TRANSLATED =
QUERY_STRING =
REMOTE_ADDR = 130.191.4.114
REMOTE_HOST = ebbsrv1p13.sdsu.edu
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 = Netscape-Commerce/1.12

Doc 18, CGI Slide # 19

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 method

The GET method sends data via the QUERY_STRING environment variable

The GET method is sent in one of two way:

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 18, CGI Slide # 20

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

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:

QUERY_STRING = name<Roger;class@cs596

Doc 18, CGI Slide # 21

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

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 18, CGI Slide # 22

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

Doc 18, CGI Slide # 23
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

CS 596: Client-Server Programming Spring Semester, 1997 Doc 18, CGI

Contents of Doc 18, CGI

References

Common Gateway Interface (CGI)

How does the Web server find and

run the CGI program?

How does the CGI program send Responses to the server?

The CGI Return Headers (CGI/1.1)

Content-type Example 1 Simple Text

Content-type Example 2 HTML

Content-type Example 3 Some Real HTML

Redirection Example 1 URL

Redirection Example 2 Path

Status Example 1

Information from the Web server to the CGI Program

Environment Variables

GET method

POST and PUT

CS 596: Client-Server Programming
Spring Semester, 1997
Doc 18, CGI