#include <errno.h>
#include <unistd.h>

int readline(int fd, char *buf, int nbytes) {
   int numread = 0;
   int returnval;

   while (numread < nbytes - 1) {
      returnval = read(fd, buf + numread, 1);
      if ((returnval == -1) && (errno == EINTR))
         continue;
      if ( (returnval == 0) && (numread == 0) )
         return 0;
      if (returnval == 0)
         break;
      if (returnval == -1)
         return -1;
      numread++;  
      if (buf[numread-1] == '\n') {
         buf[numread] = '\0';
         return numread; 
      }  
   }    
   errno = EINVAL;
   return -1;
}