BIO_ctrl(3)                  OpenSSL                  BIO_ctrl(3)


     BIO_ctrl, BIO_callback_ctrl, BIO_ptr_ctrl, BIO_int_ctrl,
     BIO_reset, BIO_seek, BIO_tell, BIO_flush, BIO_eof,
     BIO_set_close, BIO_get_close, BIO_pending, BIO_wpending,
     BIO_ctrl_pending, BIO_ctrl_wpending, BIO_get_info_callback,
     BIO_set_info_callback - BIO control operations


      #include <openssl/bio.h>

      long BIO_ctrl(BIO *bp,int cmd,long larg,void *parg);
      long BIO_callback_ctrl(BIO *b, int cmd, void (*fp)(struct bio_st *, int, const char *, int, long, long));
      char * BIO_ptr_ctrl(BIO *bp,int cmd,long larg);
      long BIO_int_ctrl(BIO *bp,int cmd,long larg,int iarg);

      int BIO_reset(BIO *b);
      int BIO_seek(BIO *b, int ofs);
      int BIO_tell(BIO *b);
      int BIO_flush(BIO *b);
      int BIO_eof(BIO *b);
      int BIO_set_close(BIO *b,long flag);
      int BIO_get_close(BIO *b);
      int BIO_pending(BIO *b);
      int BIO_wpending(BIO *b);
      size_t BIO_ctrl_pending(BIO *b);
      size_t BIO_ctrl_wpending(BIO *b);

      int BIO_get_info_callback(BIO *b,bio_info_cb **cbp);
      int BIO_set_info_callback(BIO *b,bio_info_cb *cb);

      typedef void bio_info_cb(BIO *b, int oper, const char *ptr, int arg1, long arg2, long arg3);


     BIO_ctrl(), BIO_callback_ctrl(), BIO_ptr_ctrl() and
     BIO_int_ctrl() are BIO "control" operations taking arguments
     of various types.  These functions are not normally called
     directly, various macros are used instead. The standard
     macros are described below, macros specific to a particular
     type of BIO are described in the specific BIOs manual page
     as well as any special features of the standard calls.

     BIO_reset() typically resets a BIO to some initial state, in
     the case of file related BIOs for example it rewinds the
     file pointer to the start of the file.

     BIO_seek() resets a file related BIO's (that is file
     descriptor and FILE BIOs) file position pointer to ofs bytes
     from start of file.

     BIO_tell() returns the current file position of a file
     related BIO.

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BIO_ctrl(3)                  OpenSSL                  BIO_ctrl(3)

     BIO_flush() normally writes out any internally buffered
     data, in some cases it is used to signal EOF and that no
     more data will be written.

     BIO_eof() returns 1 if the BIO has read EOF, the precise
     meaning of "EOF" varies according to the BIO type.

     BIO_set_close() sets the BIO b close flag to flag. flag can
     take the value BIO_CLOSE or BIO_NOCLOSE. Typically BIO_CLOSE
     is used in a source/sink BIO to indicate that the underlying
     I/O stream should be closed when the BIO is freed.

     BIO_get_close() returns the BIOs close flag.

     BIO_pending(), BIO_ctrl_pending(), BIO_wpending() and
     BIO_ctrl_wpending() return the number of pending characters
     in the BIOs read and write buffers.  Not all BIOs support
     these calls. BIO_ctrl_pending() and BIO_ctrl_wpending()
     return a size_t type and are functions, BIO_pending() and
     BIO_wpending() are macros which call BIO_ctrl().


     BIO_reset() normally returns 1 for success and 0 or -1 for
     failure. File BIOs are an exception, they return 0 for
     success and -1 for failure.

     BIO_seek() and BIO_tell() both return the current file
     position on success and -1 for failure, except file BIOs
     which for BIO_seek() always return 0 for success and -1 for

     BIO_flush() returns 1 for success and 0 or -1 for failure.

     BIO_eof() returns 1 if EOF has been reached 0 otherwise.

     BIO_set_close() always returns 1.

     BIO_get_close() returns the close flag value: BIO_CLOSE or

     BIO_pending(), BIO_ctrl_pending(), BIO_wpending() and
     BIO_ctrl_wpending() return the amount of pending data.


     BIO_flush(), because it can write data may return 0 or -1
     indicating that the call should be retried later in a
     similar manner to BIO_write(). The BIO_should_retry() call
     should be used and appropriate action taken is the call

     The return values of BIO_pending() and BIO_wpending() may
     not reliably determine the amount of pending data in all

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BIO_ctrl(3)                  OpenSSL                  BIO_ctrl(3)

     cases. For example in the case of a file BIO some data may
     be available in the FILE structures internal buffers but it
     is not possible to determine this in a portably way. For
     other types of BIO they may not be supported.

     Filter BIOs if they do not internally handle a particular
     BIO_ctrl() operation usually pass the operation to the next
     BIO in the chain.  This often means there is no need to
     locate the required BIO for a particular operation, it can
     be called on a chain and it will be automatically passed to
     the relevant BIO. However this can cause unexpected results:
     for example no current filter BIOs implement BIO_seek(), but
     this may still succeed if the chain ends in a FILE or file
     descriptor BIO.

     Source/sink BIOs return an 0 if they do not recognize the
     BIO_ctrl() operation.


     Some of the return values are ambiguous and care should be
     taken. In particular a return value of 0 can be returned if
     an operation is not supported, if an error occurred, if EOF
     has not been reached and in the case of BIO_seek() on a file
     BIO for a successful operation.



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