1BIO_S_BIO(3)                        OpenSSL                       BIO_S_BIO(3)
2
3
4

NAME

6       BIO_s_bio, BIO_make_bio_pair, BIO_destroy_bio_pair, BIO_shutdown_wr,
7       BIO_set_write_buf_size, BIO_get_write_buf_size, BIO_new_bio_pair,
8       BIO_get_write_guarantee, BIO_ctrl_get_write_guarantee,
9       BIO_get_read_request, BIO_ctrl_get_read_request,
10       BIO_ctrl_reset_read_request - BIO pair BIO
11

SYNOPSIS

13        #include <openssl/bio.h>
14
15        const BIO_METHOD *BIO_s_bio(void);
16
17        int BIO_make_bio_pair(BIO *b1, BIO *b2);
18        int BIO_destroy_bio_pair(BIO *b);
19        int BIO_shutdown_wr(BIO *b);
20
21        int BIO_set_write_buf_size(BIO *b, long size);
22        size_t BIO_get_write_buf_size(BIO *b, long size);
23
24        int BIO_new_bio_pair(BIO **bio1, size_t writebuf1, BIO **bio2, size_t writebuf2);
25
26        int BIO_get_write_guarantee(BIO *b);
27        size_t BIO_ctrl_get_write_guarantee(BIO *b);
28        int BIO_get_read_request(BIO *b);
29        size_t BIO_ctrl_get_read_request(BIO *b);
30        int BIO_ctrl_reset_read_request(BIO *b);
31

DESCRIPTION

33       BIO_s_bio() returns the method for a BIO pair. A BIO pair is a pair of
34       source/sink BIOs where data written to either half of the pair is
35       buffered and can be read from the other half. Both halves must usually
36       by handled by the same application thread since no locking is done on
37       the internal data structures.
38
39       Since BIO chains typically end in a source/sink BIO it is possible to
40       make this one half of a BIO pair and have all the data processed by the
41       chain under application control.
42
43       One typical use of BIO pairs is to place TLS/SSL I/O under application
44       control, this can be used when the application wishes to use a non
45       standard transport for TLS/SSL or the normal socket routines are
46       inappropriate.
47
48       Calls to BIO_read_ex() will read data from the buffer or request a
49       retry if no data is available.
50
51       Calls to BIO_write_ex() will place data in the buffer or request a
52       retry if the buffer is full.
53
54       The standard calls BIO_ctrl_pending() and BIO_ctrl_wpending() can be
55       used to determine the amount of pending data in the read or write
56       buffer.
57
58       BIO_reset() clears any data in the write buffer.
59
60       BIO_make_bio_pair() joins two separate BIOs into a connected pair.
61
62       BIO_destroy_pair() destroys the association between two connected BIOs.
63       Freeing up any half of the pair will automatically destroy the
64       association.
65
66       BIO_shutdown_wr() is used to close down a BIO b. After this call no
67       further writes on BIO b are allowed (they will return an error). Reads
68       on the other half of the pair will return any pending data or EOF when
69       all pending data has been read.
70
71       BIO_set_write_buf_size() sets the write buffer size of BIO b to size.
72       If the size is not initialized a default value is used. This is
73       currently 17K, sufficient for a maximum size TLS record.
74
75       BIO_get_write_buf_size() returns the size of the write buffer.
76
77       BIO_new_bio_pair() combines the calls to BIO_new(), BIO_make_bio_pair()
78       and BIO_set_write_buf_size() to create a connected pair of BIOs bio1,
79       bio2 with write buffer sizes writebuf1 and writebuf2. If either size is
80       zero then the default size is used.  BIO_new_bio_pair() does not check
81       whether bio1 or bio2 do point to some other BIO, the values are
82       overwritten, BIO_free() is not called.
83
84       BIO_get_write_guarantee() and BIO_ctrl_get_write_guarantee() return the
85       maximum length of data that can be currently written to the BIO. Writes
86       larger than this value will return a value from BIO_write_ex() less
87       than the amount requested or if the buffer is full request a retry.
88       BIO_ctrl_get_write_guarantee() is a function whereas
89       BIO_get_write_guarantee() is a macro.
90
91       BIO_get_read_request() and BIO_ctrl_get_read_request() return the
92       amount of data requested, or the buffer size if it is less, if the last
93       read attempt at the other half of the BIO pair failed due to an empty
94       buffer.  This can be used to determine how much data should be written
95       to the BIO so the next read will succeed: this is most useful in
96       TLS/SSL applications where the amount of data read is usually
97       meaningful rather than just a buffer size. After a successful read this
98       call will return zero.  It also will return zero once new data has been
99       written satisfying the read request or part of it.  Note that
100       BIO_get_read_request() never returns an amount larger than that
101       returned by BIO_get_write_guarantee().
102
103       BIO_ctrl_reset_read_request() can also be used to reset the value
104       returned by BIO_get_read_request() to zero.
105

NOTES

107       Both halves of a BIO pair should be freed. That is even if one half is
108       implicit freed due to a BIO_free_all() or SSL_free() call the other
109       half needs to be freed.
110
111       When used in bidirectional applications (such as TLS/SSL) care should
112       be taken to flush any data in the write buffer. This can be done by
113       calling BIO_pending() on the other half of the pair and, if any data is
114       pending, reading it and sending it to the underlying transport. This
115       must be done before any normal processing (such as calling select() )
116       due to a request and BIO_should_read() being true.
117
118       To see why this is important consider a case where a request is sent
119       using BIO_write_ex() and a response read with BIO_read_ex(), this can
120       occur during an TLS/SSL handshake for example. BIO_write_ex() will
121       succeed and place data in the write buffer. BIO_read_ex() will
122       initially fail and BIO_should_read() will be true. If the application
123       then waits for data to be available on the underlying transport before
124       flushing the write buffer it will never succeed because the request was
125       never sent!
126
127       BIO_eof() is true if no data is in the peer BIO and the peer BIO has
128       been shutdown.
129
130       BIO_make_bio_pair(), BIO_destroy_bio_pair(), BIO_shutdown_wr(),
131       BIO_set_write_buf_size(), BIO_get_write_buf_size(),
132       BIO_get_write_guarantee(), and BIO_get_read_request() are implemented
133       as macros.
134

RETURN VALUES

136       BIO_new_bio_pair() returns 1 on success, with the new BIOs available in
137       bio1 and bio2, or 0 on failure, with NULL pointers stored into the
138       locations for bio1 and bio2. Check the error stack for more
139       information.
140
141       [XXXXX: More return values need to be added here]
142

EXAMPLES

144       The BIO pair can be used to have full control over the network access
145       of an application. The application can call select() on the socket as
146       required without having to go through the SSL-interface.
147
148        BIO *internal_bio, *network_bio;
149
150        ...
151        BIO_new_bio_pair(&internal_bio, 0, &network_bio, 0);
152        SSL_set_bio(ssl, internal_bio, internal_bio);
153        SSL_operations(); /* e.g. SSL_read and SSL_write */
154        ...
155
156        application |   TLS-engine
157           |        |
158           +----------> SSL_operations()
159                    |     /\    ||
160                    |     ||    \/
161                    |   BIO-pair (internal_bio)
162                    |   BIO-pair (network_bio)
163                    |     ||     /\
164                    |     \/     ||
165           +-----------< BIO_operations()
166           |        |
167           |        |
168          socket
169
170         ...
171         SSL_free(ssl);                /* implicitly frees internal_bio */
172         BIO_free(network_bio);
173         ...
174
175       As the BIO pair will only buffer the data and never directly access the
176       connection, it behaves nonblocking and will return as soon as the write
177       buffer is full or the read buffer is drained. Then the application has
178       to flush the write buffer and/or fill the read buffer.
179
180       Use the BIO_ctrl_pending(), to find out whether data is buffered in the
181       BIO and must be transferred to the network. Use
182       BIO_ctrl_get_read_request() to find out, how many bytes must be written
183       into the buffer before the SSL_operation() can successfully be
184       continued.
185

WARNINGS

187       As the data is buffered, SSL_operation() may return with an
188       ERROR_SSL_WANT_READ condition, but there is still data in the write
189       buffer. An application must not rely on the error value of
190       SSL_operation() but must assure that the write buffer is always flushed
191       first. Otherwise a deadlock may occur as the peer might be waiting for
192       the data before being able to continue.
193

SEE ALSO

195       SSL_set_bio(3), ssl(7), bio(7), BIO_should_retry(3), BIO_read_ex(3)
196
198       Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
199
200       Licensed under the OpenSSL license (the "License").  You may not use
201       this file except in compliance with the License.  You can obtain a copy
202       in the file LICENSE in the source distribution or at
203       <https://www.openssl.org/source/license.html>.
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2071.1.1q                            2022-07-07                      BIO_S_BIO(3)
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