#ifndef _GNU_SOURCE
#warning >> sorry, but this will only compile with gnu-libc! <<
#error >> compile with   gcc -D_GNU_SOURCE <<
#else

/*------------------------------------------------------------------*\
   
  author: mathias gumz
  date: 040129 15:17:57 
  about:
    demonstrates the usage of the fopencookie-funktions/extension of
    gnu-libc to write own filehandlers


    !!! THIS CODE WILL NOT WORK ON NON_GNU_LIBC_SYSTEMS !!!
  
\*------------------------------------------------------------------*/

#include <stdio.h>
#include <libio.h>  /* essential header */

/*------------------------------------------------------------------*\
   passthru functions just to see if it works in general 
\*------------------------------------------------------------------*/
static size_t passThruRead(void* myhandle, char* buffer, size_t size)
{
  return fread(buffer, 1, size, (FILE*)myhandle);
}
static size_t passThruWrite(void* myhandle, char* buffer, size_t size)
{
  return fwrite(buffer, 1, size, (FILE*)myhandle);
}
static int passThruSeek(void* myhandle, fpos_t* position, int whence)
{
  return fseek((FILE*)myhandle, *(unsigned int*)position, whence);
}
static int passThruClose(void* myhandle)
{
  return fclose((FILE*)myhandle);
}

cookie_io_functions_t passThruFunctions= 
{ 
  (cookie_read_function_t*)passThruRead, 
  (cookie_write_function_t*)passThruWrite, 
  (cookie_seek_function_t*)passThruSeek, 
  (cookie_close_function_t*)passThruClose
};




/*------------------------------------------------------------------*\
   my own reader/writer .. shifts each written byte 1 left
                                       read    byte 1 right 
\*------------------------------------------------------------------*/
static size_t myShiftRead(void* myhandle, char* buffer, size_t size)
{
  register size_t i;
  int             ret;

  ret= fread(buffer, 1, size, (FILE*)myhandle);
  if ( !ferror((FILE*)myhandle) )
  {
    for ( i= 0; i < ret; i++ )
    {
      buffer[i]= buffer[i] >> 1;
    } 
  }
  return ret;
}

/* TODO fix this function .. atm just a first and quick try */
static size_t myShiftWrite(void* myhandle, const char* buffer, size_t size)
{
  register size_t i;
  char            c;
  for ( i= 0; i < size; i++ )
  {
    c= buffer[i] << 1;
    if ( (fwrite(&c, 1, 1, (FILE*)myhandle)) != 1 )
      return -1;
  }
  return i;
}

static int myShiftSeek(void* myhandle, fpos_t* position, int whence)
{
  return fseek((FILE*)myhandle, *(unsigned long*)position, whence);
}
  
static int myShiftClose(void* myhandle)
{
  return fclose((FILE*)myhandle);
}

cookie_io_functions_t myIOFunctions= 
{ 
  (cookie_read_function_t*)myShiftRead, 
  (cookie_write_function_t*)myShiftWrite, 
  (cookie_seek_function_t*)myShiftSeek, 
  (cookie_close_function_t*)myShiftClose
};



/*------------------------------------------------------------------*\
   main :) 
\*------------------------------------------------------------------*/
int main()
{
  FILE* n_file1;  /* normal handle */
  FILE* n_file2;  /* normal handle */

  FILE* bs_file;  /* handle for bitshifted read/write */
  FILE* pt_file;  /* handle for passthru   read/write */
  
  char  c;

  /* ordenary filehandles */
  n_file1= fopen("fcookie.c", "r");
  n_file2= fopen("fcookie.c", "r");
  
  bs_file= fopencookie(n_file1, "r", myIOFunctions);
  pt_file= fopencookie(n_file2, "r", passThruFunctions);

  while ( !feof(pt_file) && !feof(bs_file) )
  {
    c= '\0';
    fread(&c, 1, 1, pt_file); 
    printf("%c | %d <=> ", ( iscntrl(c) ? '@' : c), c); 
    c= '\0';
    fread(&c, 1, 1, bs_file);
    printf("%d | %c\n", c, ( iscntrl(c) ? '@' : c));
  }
  fclose(pt_file);
  fclose(bs_file); 
  
  return 0;
}
#endif

/* 
   vim:ts=2:sw=2:tw=80:ft=c 
 */