BIO_ctrl(3) — Subroutines

NAME

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

SYNOPSIS

#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 );

DESCRIPTION

The BIO_ctrl(), BIO_callback_ctrl(), BIO_ptr_ctrl(), and BIO_int_ctrl() functions are BIO control operations taking arguments of various types. These functions are not usually 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 reference page, as well as any special features of the standard calls.

The BIO_reset()function 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.

The BIO_seek() function resets a file related BIO’s (its file descriptor and FILE BIOs) file position pointer to ofs bytes from start of file.

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

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

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

The BIO_set_close() function 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.

The BIO_get_close() function returns the BIO’s close flag.

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

NOTES

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

The return values of the BIO_pending() and BIO_wpending() functions might 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 portably way. For other types of BIO they might 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 might 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.

RESTRICTIONS

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.

RETURN VALUES

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 failure.

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_NOCLOSE.

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

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