IBM AS/400E How CGI Programs Work

How CGI Programs Work

Most CGI programs include the following three stages:

vParsing CGI programs

vData manipulation within a CGI program

vResponse generation by a CGI program

Parsing is the first stage of a CGI program. In this stage, the program takes the

data from QUERY_STRING environment variable, command line arguments using

argv() or standard input. When the method is GET, the system reads the data from

the QUERY_STRING environment variable or command line arguments by using

argv(). There is no way to determine the length of data in QUERY_STRING. The

system encodes the QUERY_STRING data in the request header.

An example of data read in the QUERY_STRING variable (%%MIXED%% mode):

NAME=Eugene+T%2E+Fox&ADDR=etfox%40ibm.net&INTEREST=RCO

Parsing breaks the fields at the ampersands and decodes the ASCII hexadecimal

characters. The results look like this:

NAME=Eugene T. Fox

ADDR=etfox@ibm.net

INTEREST=RCO

You can use the QtmhCvtDb API to parse the information into a structure.The

CGI program can refer to the structure fields. If using %%MIXED%% input mode,

the “%xx”encoding values are in ASCII and must be converted into the “%xx”

EBCDIC encoding values before calling QtmhCvtDb. If using %%EBCDIC%%

mode, the server will do this conversion for you. The system converts ASCII

“%xx”first to the ASCII character and then to the EBCDIC character. Ultimately,

the system sets the EBCDIC character to the “%xx”in the EBCDIC CCSID. For

code samples, use the following URL to the AS/400 web site:

http://www.as400.ibm.com/tstudio/index.htm.

When the method is post, the system reads the data from standard input. Before

the CGI attempts to read standard input, it must check environment variables

REQUEST_METHOD and CONTENT_LENGTH. Read standard input only when

the REQUEST_METHOD is POST. The read must specify no more than

CONTENT_LENGTH bytes. Attempts to specify more than CONTENT_LENGTH

bytes on reading standard input are not defined.

Data manipulation is the second stage of a CGI program. In this stage, the

program takes the parsed data and performs the appropriate action. For example, a

CGI program designed to process an application form might perform one of the

following functions:

1. Take the input from the parsing stage

2. Convert abbreviations into more meaningful information

3. Plug the information into an e-mail template

4. Use SNDDST to send the e-mail.

Response generation is the final stage of a CGI program. In this stage, the program

formulates its response to the web server, which forwards it to the browser. The

response contains MIME headers that vary depending on the type of response.

12 WebProgramming Guide V4R5