Custom 404 response for GWAN

Question 1

Just like Gil said. You can use HDL_HTTP_ERRORS to intercept HTTP errors. To make it more clear here is a sample connection handler that replaces 404 error with a custom error message.

#include "gwan.h" 
int init(int argc, char *argv[])
{
   u32 *states = (u32*)get_env(argv, US_HANDLER_STATES);
   *states =  (1 << HDL_HTTP_ERRORS);
   return 0;
}

int main(int argc, char *argv[])
{
   if((long)argv[0] != HDL_HTTP_ERRORS)
      return 255; // Continue if not an error

   // get the HTTP reply code
   int *status = (int*)get_env(argv, HTTP_CODE);
   if(!status || *status != 404)
      return 255; // Continue if not a 404 error

   static char custom_err[] = 
      "<!DOCTYPE HTML><html><head><title>404 Not Found</title><meta http-equiv=\"Content-Type\" content=\"text/html; charset=utf-8\"><link href=\"/imgs/errors.css\" rel=\"stylesheet\" type=\"text/css\"></head>"
      "<body><h1>Not Found</h1>"
      "<p>This is a custom 404 not found error. What makes you think that this link exist?!!</p></body></html>";

   static char header[] = 
      "HTTP/1.1 %s\r\n"
      "Server:  G-WAN\r\n"
      "Date: %s\r\n"
      "Content-Type:  text/html; charset=UTF-8\r\n"
      "Content-Length: %u\r\n\r\n";

   int len = sizeof(custom_err)-1;
   char *date = (char*)get_env(argv, SERVER_DATE);
   // Set our http reply headers
   build_headers(argv, header,
             http_status(*status),
             date, // current server date
             len); // Reply length

   // Set our reply using our custom error
   set_reply(argv, custom_err, len, *status);

   return 2; // End request then send reply
}

void clean(int argc, char *argv[]) {}

Take note if you are returning a 404 error from a servlet. Make sure you do a

xbuf_empty(get_reply(argv));

to empty the contents of the reply buffer. It will not reach HDL_HTTP_ERRORS if there are any content on the reply buffer. It will just reply with whatever the reply buffer has.

Question 2

Both Content-Type and Connections handlers can check if the resource exists before serving it.

But the HDL_HTTP_ERRORS state of Connection Handlers lets you intercept HTTP errors to alter the default reply otherwise generated by G-WAN. It is defined in the documented G-WAN API Handler States.

That's most probably what you are looking for.