xref: /openssl/doc/man3/BIO_ctrl.pod (revision 45ada6b9) 
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, BIO_set_conn_mode, BIO_get_conn_mode, BIO_set_tfo
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 void *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 int BIO_set_conn_mode(BIO *b, int mode);
42 int BIO_get_conn_mode(BIO *b);
43
44 int BIO_set_tfo(BIO *b, int onoff);
45
46=head1 DESCRIPTION
47
48BIO_ctrl(), BIO_callback_ctrl(), BIO_ptr_ctrl() and BIO_int_ctrl()
49are BIO "control" operations taking arguments of various types.
50These functions are not normally called directly, various macros
51are used instead. The standard macros are described below, macros
52specific to a particular type of BIO are described in the specific
53BIOs manual page as well as any special features of the standard
54calls.
55
56BIO_reset() typically resets a BIO to some initial state, in the case
57of file related BIOs for example it rewinds the file pointer to the
58start of the file.
59
60BIO_seek() resets a file related BIO's (that is file descriptor and
61FILE BIOs) file position pointer to B<ofs> bytes from start of file.
62
63BIO_tell() returns the current file position of a file related BIO.
64
65BIO_flush() normally writes out any internally buffered data, in some
66cases it is used to signal EOF and that no more data will be written.
67
68BIO_eof() returns 1 if the BIO has read EOF, the precise meaning of
69"EOF" varies according to the BIO type.
70
71BIO_set_close() sets the BIO B<b> close flag to B<flag>. B<flag> can
72take the value BIO_CLOSE or BIO_NOCLOSE. Typically BIO_CLOSE is used
73in a source/sink BIO to indicate that the underlying I/O stream should
74be closed when the BIO is freed.
75
76BIO_get_close() returns the BIOs close flag.
77
78BIO_pending(), BIO_ctrl_pending(), BIO_wpending() and BIO_ctrl_wpending()
79return the number of pending characters in the BIOs read and write buffers.
80Not all BIOs support these calls. BIO_ctrl_pending() and BIO_ctrl_wpending()
81return a size_t type and are functions, BIO_pending() and BIO_wpending() are
82macros which call BIO_ctrl().
83
84BIO_get_ktls_send() returns 1 if the BIO is using the Kernel TLS data-path for
85sending. Otherwise, it returns zero.
86BIO_get_ktls_recv() returns 1 if the BIO is using the Kernel TLS data-path for
87receiving. Otherwise, it returns zero.
88
89BIO_get_conn_mode() returns the BIO connection mode. BIO_set_conn_mode() sets
90the BIO connection mode.
91
92BIO_set_tfo() disables TCP Fast Open when B<onoff> is 0, and enables TCP Fast
93Open when B<onoff> is nonzero. Setting the value to 1 is equivalent to setting
94B<BIO_SOCK_TFO> in BIO_set_conn_mode().
95
96=head1 RETURN VALUES
97
98BIO_reset() normally returns 1 for success and <=0 for failure. File
99BIOs are an exception, they return 0 for success and -1 for failure.
100
101BIO_seek() and BIO_tell() both return the current file position on success
102and -1 for failure, except file BIOs which for BIO_seek() always return 0
103for success and -1 for failure.
104
105BIO_flush() returns 1 for success and <=0 for failure.
106
107BIO_eof() returns 1 if EOF has been reached, 0 if not, or negative values for failure.
108
109BIO_set_close() returns 1 on success or <=0 for failure.
110
111BIO_get_close() returns the close flag value: BIO_CLOSE or BIO_NOCLOSE. It also
112returns other negative values if an error occurs.
113
114BIO_pending(), BIO_ctrl_pending(), BIO_wpending() and BIO_ctrl_wpending()
115return the amount of pending data. BIO_pending() and BIO_wpending() return
116negative value or 0 on error. BIO_ctrl_pending() and BIO_ctrl_wpending() return
1170 on error.
118
119BIO_get_ktls_send() returns 1 if the BIO is using the Kernel TLS data-path for
120sending. Otherwise, it returns zero.
121BIO_get_ktls_recv() returns 1 if the BIO is using the Kernel TLS data-path for
122receiving. Otherwise, it returns zero.
123
124BIO_set_conn_mode() returns 1 for success and 0 for failure. BIO_get_conn_mode()
125returns the current connection mode. Which may contain the bitwise-or of the
126following flags:
127
128 BIO_SOCK_REUSEADDR
129 BIO_SOCK_V6_ONLY
130 BIO_SOCK_KEEPALIVE
131 BIO_SOCK_NONBLOCK
132 BIO_SOCK_NODELAY
133 BIO_SOCK_TFO
134
135BIO_set_tfo() returns 1 for success, and 0 for failure.
136
137=head1 NOTES
138
139BIO_flush(), because it can write data may return 0 or -1 indicating
140that the call should be retried later in a similar manner to BIO_write_ex().
141The BIO_should_retry() call should be used and appropriate action taken
142is the call fails.
143
144The return values of BIO_pending() and BIO_wpending() may not reliably
145determine the amount of pending data in all cases. For example in the
146case of a file BIO some data may be available in the FILE structures
147internal buffers but it is not possible to determine this in a
148portably way. For other types of BIO they may not be supported.
149
150Filter BIOs if they do not internally handle a particular BIO_ctrl()
151operation usually pass the operation to the next BIO in the chain.
152This often means there is no need to locate the required BIO for
153a particular operation, it can be called on a chain and it will
154be automatically passed to the relevant BIO. However, this can cause
155unexpected results: for example no current filter BIOs implement
156BIO_seek(), but this may still succeed if the chain ends in a FILE
157or file descriptor BIO.
158
159Source/sink BIOs return an 0 if they do not recognize the BIO_ctrl()
160operation.
161
162=head1 BUGS
163
164Some of the return values are ambiguous and care should be taken. In
165particular a return value of 0 can be returned if an operation is not
166supported, if an error occurred, if EOF has not been reached and in
167the case of BIO_seek() on a file BIO for a successful operation.
168
169In older versions of OpenSSL the BIO_ctrl_pending() and
170BIO_ctrl_wpending() could return values greater than INT_MAX on error.
171
172=head1 HISTORY
173
174The BIO_get_ktls_send() and BIO_get_ktls_recv() macros were added in
175OpenSSL 3.0. They were modified to never return -1 in OpenSSL 3.0.4.
176
177The BIO_get_conn_mode(), BIO_set_conn_mode() and BIO_set_tfo() functions
178were added in OpenSSL 3.2.
179
180=head1 COPYRIGHT
181
182Copyright 2000-2022 The OpenSSL Project Authors. All Rights Reserved.
183
184Licensed under the Apache License 2.0 (the "License").  You may not use
185this file except in compliance with the License.  You can obtain a copy
186in the file LICENSE in the source distribution or at
187L<https://www.openssl.org/source/license.html>.
188
189=cut
190