Chapter 11, Problem 11.12HW

Program Plan Intro

IP addresses:

• The IP address denotes an unsigned integer that is 32-bit.
• The IP addresses is been stored by network programs in IP address structure.
• The addresses present in IP address structure are stored in network byte order.
•  An unsigned 32-bit integer is transformed from host byte order to network byte order by “htonl” function.
• An unsigned 32-bit integer is transformed from network byte order host byte order by “ntohl” function.
• The IP address is presented to humans in a form known as “dotted-decimal” notation.
  • Each byte is been represented by its corresponding decimal value and is separated by a period from other bytes.

Passing program arguments to server:

• The arguments for “GET” requests are passed in the URI.
• The character “?” separates filename from the arguments.
• The character “&” separates each argument.
• The arguments do not allow spaces in it.

Server passes arguments to child:

• The server calls “fork” to create a child process and calls “execve” to run program in child’s context once it receives a request.
• The child process sets CGI environment variable values.
• The “adder” program can reference it at run time using “getenv” function of linux.

Output is sent by child:

• The dynamic content of a CGI program is to be sent to standard output.
• A CGI program sends dynamic content to standard output.
• It uses “dup2” function for redirecting standard output to connected descriptor associated with client.
• The result written to standard output by CGI program, it goes directly to client.