NAME

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_info_cb, bio_info_cb — BIO control operations

SYNOPSIS

#include <openssl/bio.h> long
BIO_ctrl(BIO *b, int cmd, long larg, void *parg); long
BIO_callback_ctrl(BIO *b, int cmd, BIO_info_cb *cb); char *
BIO_ptr_ctrl(BIO *b, int cmd, long larg); long
BIO_int_ctrl(BIO *b, 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 int
BIO_info_cb(BIO *b, int state, int res); typedef int
bio_info_cb(BIO *b, int state, int res);

DESCRIPTION

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 BIO's manual page as well as any special features of the standard calls. Depending on the cmd and on the type of b, BIO_ctrl() may have a read-only effect on b or change data in b or in its sub-structures. It may also have a side effect of changing the memory pointed to by parg. BIO_callback_ctrl() does not call BIO_ctrl() but instead requires that the BIO type of b provides a dedicated callback_ctrl function pointer, which is built into the library for some standard BIO types and can be provided with BIO_meth_set_callback_ctrl(3) for application-defined BIO types. The only cmd supported by BIO_callback_ctrl() is BIO_CTRL_SET_CALLBACK. BIO_ptr_ctrl() calls BIO_ctrl() with parg pointing to the location of a temporary pointer variable initialized to NULL. BIO_int_ctrl() calls BIO_ctrl() with parg pointing to the location of a temporary int variable initialized to iarg. If BIO_ctrl() changes the value stored at *parg, the new value is ignored. 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. 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 BIO's close flag. BIO_pending(), BIO_ctrl_pending(), BIO_wpending(), and BIO_ctrl_wpending() return the number of pending characters in the BIO's 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_set_info_callback() installs the function pointer cb as an info callback in b by calling BIO_callback_ctrl() with a command of BIO_CTRL_SET_CALLBACK. Among the BIO types built into the library, only BIO_s_connect(3) and BIO_f_ssl(3) support this functionality. Some filter BIO types forward this control call to the next BIO in the chain instead of processing it themselves. BIO_get_info_callback() places the function pointer to the info callback into *cbp if any was installed using BIO_set_info_callback() or BIO_callback_ctrl(). If the type of b supports setting an info callback but none was installed, it stores a NULL pointer in *cbp. The function type name bio_info_cb is a deprecated synonym for BIO_info_cb provided for backward compatibility with some existing application software. The following cmd constants correspond to macros:

cmd constant	corresponding macro
BIO_C_DESTROY_BIO_PAIR	BIO_destroy_bio_pair(3)
BIO_C_DO_STATE_MACHINE	BIO_do_handshake(3)
BIO_C_FILE_SEEK	BIO_seek()
BIO_C_FILE_TELL	BIO_tell()
BIO_C_GET_ACCEPT	BIO_get_accept_port(3)
BIO_C_GET_BIND_MODE	BIO_get_bind_mode(3)
BIO_C_GET_BUF_MEM_PTR	BIO_get_mem_ptr(3)
BIO_C_GET_BUFF_NUM_LINES	BIO_get_buffer_num_lines(3)
BIO_C_GET_CIPHER_CTX	BIO_get_cipher_ctx(3)
BIO_C_GET_CIPHER_STATUS	BIO_get_cipher_status(3)
BIO_C_GET_FD	BIO_get_fd(3)
BIO_C_GET_FILE_PTR	BIO_get_fp(3)
BIO_C_GET_MD	BIO_get_md(3)
BIO_C_GET_MD_CTX	BIO_get_md_ctx(3)
BIO_C_GET_READ_REQUEST	BIO_get_read_request(3)
BIO_C_GET_SSL	BIO_get_ssl(3)
BIO_C_GET_SSL_NUM_RENEGOTIATES	BIO_get_num_renegotiates(3)
BIO_C_GET_WRITE_BUF_SIZE	BIO_get_write_buf_size(3)
BIO_C_GET_WRITE_GUARANTEE	BIO_get_write_guarantee(3)
BIO_C_MAKE_BIO_PAIR	BIO_make_bio_pair(3)
BIO_C_RESET_READ_REQUEST	BIO_ctrl_reset_read_request(3)
BIO_C_SET_BIND_MODE	BIO_set_bind_mode(3)
BIO_C_SET_BUF_MEM	BIO_set_mem_buf(3)
BIO_C_SET_BUF_MEM_EOF_RETURN	BIO_set_mem_eof_return(3)
BIO_C_SET_BUFF_READ_DATA	BIO_set_buffer_read_data(3)
BIO_C_SET_FD	BIO_set_fd(3)
BIO_C_SET_FILE_PTR	BIO_set_fp(3)
BIO_C_SET_MD	BIO_set_md(3)
BIO_C_SET_MD_CTX	BIO_set_md_ctx(3)
BIO_C_SET_NBIO	BIO_set_nbio(3)
BIO_C_SET_SSL	BIO_set_ssl(3)
BIO_C_SET_SSL_RENEGOTIATE_BYTES	BIO_set_ssl_renegotiate_bytes(3)
BIO_C_SET_SSL_RENEGOTIATE_TIMEOUT	BIO_set_ssl_renegotiate_timeout(3)
BIO_C_SET_WRITE_BUF_SIZE	BIO_set_write_buf_size(3)
BIO_C_SHUTDOWN_WR	BIO_shutdown_wr(3)
BIO_C_SSL_MODE	BIO_set_ssl_mode(3)
BIO_CTRL_DGRAM_CONNECT	BIO_ctrl_dgram_connect(3)
BIO_CTRL_DGRAM_GET_PEER	BIO_dgram_get_peer(3)
BIO_CTRL_DGRAM_GET_RECV_TIMER_EXP	BIO_dgram_recv_timedout(3)
BIO_CTRL_DGRAM_GET_SEND_TIMER_EXP	BIO_dgram_send_timedout(3)
BIO_CTRL_DGRAM_SET_CONNECTED	BIO_ctrl_set_connected(3)
BIO_CTRL_DGRAM_SET_PEER	BIO_dgram_set_peer(3)
BIO_CTRL_DUP	BIO_dup_state(3)
BIO_CTRL_EOF	BIO_eof()
BIO_CTRL_FLUSH	BIO_flush()
BIO_CTRL_GET_CALLBACK	BIO_get_info_callback()
BIO_CTRL_GET_CLOSE	BIO_get_close()
BIO_CTRL_INFO	BIO_get_mem_data(3)
BIO_CTRL_PENDING	BIO_pending()
BIO_CTRL_RESET	BIO_reset()
BIO_CTRL_SET_CALLBACK	BIO_set_info_callback()
BIO_CTRL_SET_CLOSE	BIO_set_close()
BIO_CTRL_WPENDING	BIO_wpending()

A few cmd constants serve more than one macro each and are documented in the following manual pages:

cmd constant	manual page
BIO_C_GET_CONNECT	BIO_s_connect(3)
BIO_C_SET_ACCEPT	BIO_s_accept(3)
BIO_C_SET_BUFF_SIZE	BIO_f_buffer(3)
BIO_C_SET_CONNECT	BIO_s_connect(3)
BIO_C_SET_FILENAME	BIO_s_file(3)

Some cmd constants are not associated with any macros. They are documented in the following manual pages:

cmd constant	manual page
BIO_CTRL_DGRAM_GET_FALLBACK_MTU	BIO_dgram_set_peer(3)
BIO_CTRL_DGRAM_GET_MTU	BIO_dgram_set_peer(3)
BIO_CTRL_DGRAM_GET_RECV_TIMEOUT	BIO_dgram_recv_timedout(3)
BIO_CTRL_DGRAM_GET_SEND_TIMEOUT	BIO_dgram_send_timedout(3)
BIO_CTRL_DGRAM_SET_MTU	BIO_dgram_set_peer(3)
BIO_CTRL_DGRAM_SET_NEXT_TIMEOUT	BIO_dgram_recv_timedout(3)
BIO_CTRL_DGRAM_SET_RECV_TIMEOUT	BIO_dgram_recv_timedout(3)
BIO_CTRL_DGRAM_SET_SEND_TIMEOUT	BIO_dgram_send_timedout(3)
BIO_CTRL_DGRAM_MTU_EXCEEDED	BIO_s_datagram(3)
BIO_CTRL_POP	BIO_pop(3)
BIO_CTRL_PUSH	BIO_push(3)

RETURN VALUES

The meaning of the return values of BIO_ctrl(), BIO_callback_ctrl(), and BIO_int_ctrl() depends on both the type of b and on the cmd. If b is a NULL pointer, no action occurs and 0 is returned. The return value -2 usually indicates a fatal error. In particular, it is returned if the cmd is unsupported by the type of b. BIO_callback_ctrl() and BIO_set_info_callback() return 1 on success, 0 if b is NULL or to indicate failure of a valid cmd, or -2 if the cmd is not supported by b. BIO_ptr_ctrl() returns NULL if the BIO_ctrl() call returns a negative value or does not change *parg, or the pointer it puts into *parg otherwise. BIO_int_ctrl() returns the return value of BIO_ctrl(). BIO_reset() normally returns 1 for success and 0 or -1 for failure. File BIOs are an exception, returning 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 failure. BIO_flush() returns 1 for success and 0 or -1 for failure. BIO_eof() returns 1 if EOF has been reached or 0 otherwise. BIO_set_close() always returns 1. BIO_get_close() returns the close flag value BIO_CLOSE or BIO_NOCLOSE. BIO_pending(), BIO_ctrl_pending(), BIO_wpending(), and BIO_ctrl_wpending() return the amount of pending data. BIO_get_info_callback() returns 1 on success, including when the type of b supports an info callback but none is installed, 0 if b is NULL or -2 if the type of b does not support an info callback. If a callback was installed in b using BIO_set_callback_ex(3) or BIO_set_callback(3), it can modify the return values of all these functions.

NOTES

Because it can write data, BIO_flush() may return 0 or -1 indicating that the call should be retried later in a similar manner to BIO_write(3). The BIO_should_retry(3) call should be used and appropriate action taken if the call fails. The return values of BIO_pending() and BIO_wpending() may not reliably determine the amount of pending data in all cases. For example in the case of a file BIO some data may be available in the FILE structure's internal buffers but it is not possible to determine this in a portable way. For other types of BIO they may not be supported. If they do not internally handle a particular BIO_ctrl() operation, filter BIOs 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 a 0 if they do not recognize the BIO_ctrl() operation.

SEE ALSO

BIO_meth_new(3), BIO_new(3)

HISTORY

BIO_ctrl(), BIO_reset(), BIO_flush(), BIO_eof(), BIO_set_close(), BIO_get_close(), and BIO_pending() first appeared in SSLeay 0.6.0. BIO_wpending() first appeared in SSLeay 0.8.1. BIO_ptr_ctrl(), BIO_int_ctrl(), BIO_get_info_callback() and BIO_set_info_callback() first appeared in SSLeay 0.9.0. All these functions have been available since OpenBSD 2.4. BIO_seek() and BIO_tell() first appeared in SSLeay 0.9.1. BIO_ctrl_pending() and BIO_ctrl_wpending() first appeared in OpenSSL 0.9.4. These functions have been available since OpenBSD 2.6. BIO_callback_ctrl() first appeared in OpenSSL 0.9.5 and has been available since OpenBSD 2.7. bio_info_cb() first appeared with a more complicated prototype in OpenSSL 0.9.6 and has been available since OpenBSD 2.9. BIO_info_cb() first appeared in OpenSSL 1.1.0h and has been available since OpenBSD 6.3.

BUGS

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.