#include <unistd.h>
#include <stdlib.h>
#include <malloc.h>
#include <string.h>

#define TCPREMOTEIP "TCPREMOTEIP="
#define RELAYCLIENT "RELAYCLIENT="
#define USAGE "usage: relaycheck <address>[,...] <program> [...]\n"

void usage ()
{
  write(2, USAGE, strlen(USAGE));
  exit(1);
}

char *realloc_or_die (char *p, size_t len)
{
  p = realloc(p, len);
  if (!p) exit(255);
  return p;
}

int main (int argc, char **argv, char **env)
{
  char **c = env,
       **newenv = NULL,
       *ip, *left, *right;
  int envlen = 1,
      i = 0;

  if (argc < 3) usage();
  if (!*argv[1] || !*argv[2]) usage();

  for (;; ++c, ++envlen) {
    newenv = (char**) realloc_or_die((char*) newenv, envlen * sizeof(char*));
    *(newenv + envlen - 1) = *c;
    if (!*c) break;

    if (i) continue;
    if (strncmp(*c, TCPREMOTEIP, strlen(TCPREMOTEIP))) continue;
    ip = strchr(*c, '=');
    if (!*++ip) continue;

    for (left = argv[1];; left = right) {
      right = strchr(left, ',');

      if (right) i = right - left;
      else i = strlen(left);

      if (i) if (!strncmp(ip, left, i)) {
        newenv = (char**) realloc_or_die((char*) newenv,
          ++envlen * sizeof(char*));

        left = realloc_or_die(NULL, strlen(RELAYCLIENT) + 1);
        strcpy(left, RELAYCLIENT);
        *(newenv + envlen - 1) = left;
        break;
      }

      i ^= i;
      if (!right) break;
      if (!*++right) break;
    }
  }

  execve(argv[2], &argv[2], newenv);
  return 1;
}