Usually, web servers provide some useful information via hidden environment variables. For example, some variables might sound familiar to you, SERVER_ADDR, REMOTE_ADDR, HTTP_USER_AGENT, HTTP_HOST, QUERY_STRING …
Check this link to see more variables.
To get value of those environment variables, use getenv() defined in stdlib.h
I wrote this code to demonstrate how it works,
/* file: get_env.c */
#include "fcgi_stdio.h"
// declare a list of environment variables
const char *ENV_VARS[] = {
"DOCUMENT_ROOT",
"HTTP_COOKIE",
"HTTP_HOST",
"HTTP_REFERER",
"HTTP_USER_AGENT",
"HTTPS",
"PATH",
"QUERY_STRING",
"REMOTE_ADDR",
"REMOTE_HOST",
"REMOTE_PORT",
"REMOTE_USER",
"REQUEST_METHOD",
"REQUEST_URI",
"SCRIPT_FILENAME",
"SCRIPT_NAME",
"SERVER_ADMIN",
"SERVER_NAME",
"SERVER_PORT",
"SERVER_SOFTWARE"
};
/**
* print out all values of correspondent env variables
*/
void printEnvVars ()
{
const char *format = "<p>%s : <strong>%s</strong></p>";
int c = 0;
for(; c < 20; ++c) {
char *s = getenv(ENV_VARS[c]);
if(s != NULL) {
printf(format, ENV_VARS[c], getenv(ENV_VARS[c]));
} else {
// no value
printf(format, ENV_VARS[c], "(No value)");
}
}
}
/* entry point */
int main ()
{
while(FCGI_Accept() >= 0) {
/* response format */
printf("Content-type: text/html"
"\r\n\r\n");
/* init html structure */
printf("<!doctype html>"
"<html lang=\"en\">");
printf("<body>");
/* show all env vars */
printEnvVars();
/* close tags */
printf("</body>");
printf("</html>");
}
return 0;
}
To build the code,
$ gcc -Wall get_env.c -lfcgi -o get_env.fcgi
and execute just like any other FastCGI application.
