1=pod
2
3=head1 NAME
4
5BIO_ctrl, BIO_callback_ctrl, BIO_ptr_ctrl, BIO_int_ctrl, BIO_reset,
6BIO_seek, BIO_tell, BIO_flush, BIO_eof, BIO_set_close, BIO_get_close,
7BIO_pending, BIO_wpending, BIO_ctrl_pending, BIO_ctrl_wpending,
8BIO_get_info_callback, BIO_set_info_callback, BIO_info_cb, BIO_get_ktls_send,
9BIO_get_ktls_recv
10- BIO control operations
11
12=head1 SYNOPSIS
13
14 #include <openssl/bio.h>
15
16 typedef int BIO_info_cb(BIO *b, int state, int res);
17
18 long BIO_ctrl(BIO *bp, int cmd, long larg, void *parg);
19 long BIO_callback_ctrl(BIO *b, int cmd, BIO_info_cb *cb);
20 char *BIO_ptr_ctrl(BIO *bp, int cmd, long larg);
21 long BIO_int_ctrl(BIO *bp, int cmd, long larg, int iarg);
22
23 int BIO_reset(BIO *b);
24 int BIO_seek(BIO *b, int ofs);
25 int BIO_tell(BIO *b);
26 int BIO_flush(BIO *b);
27 int BIO_eof(BIO *b);
28 int BIO_set_close(BIO *b, long flag);
29 int BIO_get_close(BIO *b);
30 int BIO_pending(BIO *b);
31 int BIO_wpending(BIO *b);
32 size_t BIO_ctrl_pending(BIO *b);
33 size_t BIO_ctrl_wpending(BIO *b);
34
35 int BIO_get_info_callback(BIO *b, BIO_info_cb **cbp);
36 int BIO_set_info_callback(BIO *b, BIO_info_cb *cb);
37
38 int BIO_get_ktls_send(BIO *b);
39 int BIO_get_ktls_recv(BIO *b);
40
41=head1 DESCRIPTION
42
43BIO_ctrl(), BIO_callback_ctrl(), BIO_ptr_ctrl() and BIO_int_ctrl()
44are BIO "control" operations taking arguments of various types.
45These functions are not normally called directly, various macros
46are used instead. The standard macros are described below, macros
47specific to a particular type of BIO are described in the specific
48BIOs manual page as well as any special features of the standard
49calls.
50
51BIO_reset() typically resets a BIO to some initial state, in the case
52of file related BIOs for example it rewinds the file pointer to the
53start of the file.
54
55BIO_seek() resets a file related BIO's (that is file descriptor and
56FILE BIOs) file position pointer to B<ofs> bytes from start of file.
57
58BIO_tell() returns the current file position of a file related BIO.
59
60BIO_flush() normally writes out any internally buffered data, in some
61cases it is used to signal EOF and that no more data will be written.
62
63BIO_eof() returns 1 if the BIO has read EOF, the precise meaning of
64"EOF" varies according to the BIO type.
65
66BIO_set_close() sets the BIO B<b> close flag to B<flag>. B<flag> can
67take the value BIO_CLOSE or BIO_NOCLOSE. Typically BIO_CLOSE is used
68in a source/sink BIO to indicate that the underlying I/O stream should
69be closed when the BIO is freed.
70
71BIO_get_close() returns the BIOs close flag.
72
73BIO_pending(), BIO_ctrl_pending(), BIO_wpending() and BIO_ctrl_wpending()
74return the number of pending characters in the BIOs read and write buffers.
75Not all BIOs support these calls. BIO_ctrl_pending() and BIO_ctrl_wpending()
76return a size_t type and are functions, BIO_pending() and BIO_wpending() are
77macros which call BIO_ctrl().
78
79BIO_get_ktls_send() returns 1 if the BIO is using the Kernel TLS data-path for
80sending. Otherwise, it returns zero. It also returns negative values for failure.
81BIO_get_ktls_recv() returns 1 if the BIO is using the Kernel TLS data-path for
82receiving. Otherwise, it returns zero. It also returns negative values for failure.
83
84=head1 RETURN VALUES
85
86BIO_reset() normally returns 1 for success and <=0 for failure. File
87BIOs are an exception, they return 0 for success and -1 for failure.
88
89BIO_seek() and BIO_tell() both return the current file position on success
90and -1 for failure, except file BIOs which for BIO_seek() always return 0
91for success and -1 for failure.
92
93BIO_flush() returns 1 for success and <=0 for failure.
94
95BIO_eof() returns 1 if EOF has been reached, 0 if not, or negative values for failure.
96
97BIO_set_close() returns 1 on success or <=0 for failure.
98
99BIO_get_close() returns the close flag value: BIO_CLOSE or BIO_NOCLOSE. It also
100returns other negative values if an error occurs.
101
102BIO_pending(), BIO_ctrl_pending(), BIO_wpending() and BIO_ctrl_wpending()
103return the amount of pending data.
104
105BIO_get_ktls_send() returns 1 if the BIO is using the Kernel TLS data-path for
106sending. Otherwise, it returns zero.
107BIO_get_ktls_recv() returns 1 if the BIO is using the Kernel TLS data-path for
108receiving. Otherwise, it returns zero.
109
110=head1 NOTES
111
112BIO_flush(), because it can write data may return 0 or -1 indicating
113that the call should be retried later in a similar manner to BIO_write_ex().
114The BIO_should_retry() call should be used and appropriate action taken
115is the call fails.
116
117The return values of BIO_pending() and BIO_wpending() may not reliably
118determine the amount of pending data in all cases. For example in the
119case of a file BIO some data may be available in the FILE structures
120internal buffers but it is not possible to determine this in a
121portably way. For other types of BIO they may not be supported.
122
123Filter BIOs if they do not internally handle a particular BIO_ctrl()
124operation usually pass the operation to the next BIO in the chain.
125This often means there is no need to locate the required BIO for
126a particular operation, it can be called on a chain and it will
127be automatically passed to the relevant BIO. However, this can cause
128unexpected results: for example no current filter BIOs implement
129BIO_seek(), but this may still succeed if the chain ends in a FILE
130or file descriptor BIO.
131
132Source/sink BIOs return an 0 if they do not recognize the BIO_ctrl()
133operation.
134
135=head1 BUGS
136
137Some of the return values are ambiguous and care should be taken. In
138particular a return value of 0 can be returned if an operation is not
139supported, if an error occurred, if EOF has not been reached and in
140the case of BIO_seek() on a file BIO for a successful operation.
141
142=head1 HISTORY
143
144The BIO_get_ktls_send() and BIO_get_ktls_recv() functions were added in
145OpenSSL 3.0.
146
147=head1 COPYRIGHT
148
149Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
150
151Licensed under the Apache License 2.0 (the "License").  You may not use
152this file except in compliance with the License.  You can obtain a copy
153in the file LICENSE in the source distribution or at
154L<https://www.openssl.org/source/license.html>.
155
156=cut
157