text: #include <fcntl.h>
  #include <string.h>
  
  #include "stdio_impl.h"
  
  FILE* __fopen_rb_ca(const char* filename, FILE* f, unsigned char* buf, size_t len) {
    memset(f, 0, sizeof *f);
  
    f->fd = open(filename, O_RDONLY | O_CLOEXEC);
    if (f->fd < 0)
      return 0;
    fcntl(f->fd, F_SETFD, FD_CLOEXEC);
  
    f->flags = F_NOWR | F_PERM;
    f->buf = buf + UNGET;
    f->buf_size = len - UNGET;
    f->read = __stdio_read;
    f->seek = __stdio_seek;
    f->close = __stdio_close;
    f->lock = -1;
  
    return f;
  }
  