openssl (3.1.3)
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VersionsBIO_S_BIO(3ossl) OpenSSL BIO_S_BIO(3ossl)
NAME
BIO_s_bio, BIO_make_bio_pair, BIO_destroy_bio_pair, BIO_shutdown_wr, BIO_set_write_buf_size,
BIO_get_write_buf_size, BIO_new_bio_pair, BIO_get_write_guarantee, BIO_ctrl_get_write_guarantee,
BIO_get_read_request, BIO_ctrl_get_read_request, BIO_ctrl_reset_read_request - BIO pair BIO
SYNOPSIS
#include <openssl/bio.h>
const BIO_METHOD *BIO_s_bio(void);
int BIO_make_bio_pair(BIO *b1, BIO *b2);
int BIO_destroy_bio_pair(BIO *b);
int BIO_shutdown_wr(BIO *b);
int BIO_set_write_buf_size(BIO *b, long size);
size_t BIO_get_write_buf_size(BIO *b, long size);
int BIO_new_bio_pair(BIO **bio1, size_t writebuf1, BIO **bio2, size_t writebuf2);
int BIO_get_write_guarantee(BIO *b);
size_t BIO_ctrl_get_write_guarantee(BIO *b);
int BIO_get_read_request(BIO *b);
size_t BIO_ctrl_get_read_request(BIO *b);
int BIO_ctrl_reset_read_request(BIO *b);
DESCRIPTION
BIO_s_bio() returns the method for a BIO pair. A BIO pair is a pair of source/sink BIOs where data written to
either half of the pair is buffered and can be read from the other half. Both halves must usually by handled by
the same application thread since no locking is done on the internal data structures.
Since BIO chains typically end in a source/sink BIO it is possible to make this one half of a BIO pair and have
all the data processed by the chain under application control.
One typical use of BIO pairs is to place TLS/SSL I/O under application control, this can be used when the
application wishes to use a non standard transport for TLS/SSL or the normal socket routines are inappropriate.
Calls to BIO_read_ex() will read data from the buffer or request a retry if no data is available.
Calls to BIO_write_ex() will place data in the buffer or request a retry if the buffer is full.
The standard calls BIO_ctrl_pending() and BIO_ctrl_wpending() can be used to determine the amount of pending data
in the read or write buffer.
BIO_reset() clears any data in the write buffer.
BIO_make_bio_pair() joins two separate BIOs into a connected pair.
BIO_destroy_pair() destroys the association between two connected BIOs. Freeing up any half of the pair will
automatically destroy the association.
BIO_shutdown_wr() is used to close down a BIO b. After this call no further writes on BIO b are allowed (they
will return an error). Reads on the other half of the pair will return any pending data or EOF when all pending
data has been read.
BIO_set_write_buf_size() sets the write buffer size of BIO b to size. If the size is not initialized a default
value is used. This is currently 17K, sufficient for a maximum size TLS record.
BIO_get_write_buf_size() returns the size of the write buffer.
BIO_new_bio_pair() combines the calls to BIO_new(), BIO_make_bio_pair() and BIO_set_write_buf_size() to create a
connected pair of BIOs bio1, bio2 with write buffer sizes writebuf1 and writebuf2. If either size is zero then
the default size is used. BIO_new_bio_pair() does not check whether bio1 or bio2 do point to some other BIO, the
values are overwritten, BIO_free() is not called.
BIO_get_write_guarantee() and BIO_ctrl_get_write_guarantee() return the maximum length of data that can be
currently written to the BIO. Writes larger than this value will return a value from BIO_write_ex() less than the
amount requested or if the buffer is full request a retry. BIO_ctrl_get_write_guarantee() is a function whereas
BIO_get_write_guarantee() is a macro.
BIO_get_read_request() and BIO_ctrl_get_read_request() return the amount of data requested, or the buffer size if
it is less, if the last read attempt at the other half of the BIO pair failed due to an empty buffer. This can
be used to determine how much data should be written to the BIO so the next read will succeed: this is most
useful in TLS/SSL applications where the amount of data read is usually meaningful rather than just a buffer
size. After a successful read this call will return zero. It also will return zero once new data has been
written satisfying the read request or part of it. Note that BIO_get_read_request() never returns an amount
larger than that returned by BIO_get_write_guarantee().
BIO_ctrl_reset_read_request() can also be used to reset the value returned by BIO_get_read_request() to zero.
NOTES
Both halves of a BIO pair should be freed. That is even if one half is implicit freed due to a BIO_free_all() or
SSL_free() call the other half needs to be freed.
When used in bidirectional applications (such as TLS/SSL) care should be taken to flush any data in the write
buffer. This can be done by calling BIO_pending() on the other half of the pair and, if any data is pending,
reading it and sending it to the underlying transport. This must be done before any normal processing (such as
calling select() ) due to a request and BIO_should_read() being true.
To see why this is important consider a case where a request is sent using BIO_write_ex() and a response read
with BIO_read_ex(), this can occur during an TLS/SSL handshake for example. BIO_write_ex() will succeed and place
data in the write buffer. BIO_read_ex() will initially fail and BIO_should_read() will be true. If the
application then waits for data to be available on the underlying transport before flushing the write buffer it
will never succeed because the request was never sent!
BIO_eof() is true if no data is in the peer BIO and the peer BIO has been shutdown.
BIO_make_bio_pair(), BIO_destroy_bio_pair(), BIO_shutdown_wr(), BIO_set_write_buf_size(),
BIO_get_write_buf_size(), BIO_get_write_guarantee(), and BIO_get_read_request() are implemented as macros.
RETURN VALUES
BIO_new_bio_pair() returns 1 on success, with the new BIOs available in bio1 and bio2, or 0 on failure, with NULL
pointers stored into the locations for bio1 and bio2. Check the error stack for more information.
[XXXXX: More return values need to be added here]
EXAMPLES
The BIO pair can be used to have full control over the network access of an application. The application can call
select() on the socket as required without having to go through the SSL-interface.
BIO *internal_bio, *network_bio;
...
BIO_new_bio_pair(&internal_bio, 0, &network_bio, 0);
SSL_set_bio(ssl, internal_bio, internal_bio);
SSL_operations(); /* e.g. SSL_read and SSL_write */
...
application | TLS-engine
| |
+----------> SSL_operations()
| /\ ||
| || \/
| BIO-pair (internal_bio)
| BIO-pair (network_bio)
| || /\
| \/ ||
+-----------< BIO_operations()
| |
| |
socket
...
SSL_free(ssl); /* implicitly frees internal_bio */
BIO_free(network_bio);
...
As the BIO pair will only buffer the data and never directly access the connection, it behaves nonblocking and
will return as soon as the write buffer is full or the read buffer is drained. Then the application has to flush
the write buffer and/or fill the read buffer.
Use the BIO_ctrl_pending(), to find out whether data is buffered in the BIO and must be transferred to the
network. Use BIO_ctrl_get_read_request() to find out, how many bytes must be written into the buffer before the
SSL_operation() can successfully be continued.
WARNINGS
As the data is buffered, SSL_operation() may return with an ERROR_SSL_WANT_READ condition, but there is still
data in the write buffer. An application must not rely on the error value of SSL_operation() but must assure that
the write buffer is always flushed first. Otherwise a deadlock may occur as the peer might be waiting for the
data before being able to continue.
SEE ALSO
SSL_set_bio(3), ssl(7), bio(7), BIO_should_retry(3), BIO_read_ex(3)
COPYRIGHT
Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the
License. You can obtain a copy in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.
3.1.3 2023-09-19 BIO_S_BIO(3ossl)
NAME
BIO_s_bio, BIO_make_bio_pair, BIO_destroy_bio_pair, BIO_shutdown_wr, BIO_set_write_buf_size,
BIO_get_write_buf_size, BIO_new_bio_pair, BIO_get_write_guarantee, BIO_ctrl_get_write_guarantee,
BIO_get_read_request, BIO_ctrl_get_read_request, BIO_ctrl_reset_read_request - BIO pair BIO
SYNOPSIS
#include <openssl/bio.h>
const BIO_METHOD *BIO_s_bio(void);
int BIO_make_bio_pair(BIO *b1, BIO *b2);
int BIO_destroy_bio_pair(BIO *b);
int BIO_shutdown_wr(BIO *b);
int BIO_set_write_buf_size(BIO *b, long size);
size_t BIO_get_write_buf_size(BIO *b, long size);
int BIO_new_bio_pair(BIO **bio1, size_t writebuf1, BIO **bio2, size_t writebuf2);
int BIO_get_write_guarantee(BIO *b);
size_t BIO_ctrl_get_write_guarantee(BIO *b);
int BIO_get_read_request(BIO *b);
size_t BIO_ctrl_get_read_request(BIO *b);
int BIO_ctrl_reset_read_request(BIO *b);
DESCRIPTION
BIO_s_bio() returns the method for a BIO pair. A BIO pair is a pair of source/sink BIOs where data written to
either half of the pair is buffered and can be read from the other half. Both halves must usually by handled by
the same application thread since no locking is done on the internal data structures.
Since BIO chains typically end in a source/sink BIO it is possible to make this one half of a BIO pair and have
all the data processed by the chain under application control.
One typical use of BIO pairs is to place TLS/SSL I/O under application control, this can be used when the
application wishes to use a non standard transport for TLS/SSL or the normal socket routines are inappropriate.
Calls to BIO_read_ex() will read data from the buffer or request a retry if no data is available.
Calls to BIO_write_ex() will place data in the buffer or request a retry if the buffer is full.
The standard calls BIO_ctrl_pending() and BIO_ctrl_wpending() can be used to determine the amount of pending data
in the read or write buffer.
BIO_reset() clears any data in the write buffer.
BIO_make_bio_pair() joins two separate BIOs into a connected pair.
BIO_destroy_pair() destroys the association between two connected BIOs. Freeing up any half of the pair will
automatically destroy the association.
BIO_shutdown_wr() is used to close down a BIO b. After this call no further writes on BIO b are allowed (they
will return an error). Reads on the other half of the pair will return any pending data or EOF when all pending
data has been read.
BIO_set_write_buf_size() sets the write buffer size of BIO b to size. If the size is not initialized a default
value is used. This is currently 17K, sufficient for a maximum size TLS record.
BIO_get_write_buf_size() returns the size of the write buffer.
BIO_new_bio_pair() combines the calls to BIO_new(), BIO_make_bio_pair() and BIO_set_write_buf_size() to create a
connected pair of BIOs bio1, bio2 with write buffer sizes writebuf1 and writebuf2. If either size is zero then
the default size is used. BIO_new_bio_pair() does not check whether bio1 or bio2 do point to some other BIO, the
values are overwritten, BIO_free() is not called.
BIO_get_write_guarantee() and BIO_ctrl_get_write_guarantee() return the maximum length of data that can be
currently written to the BIO. Writes larger than this value will return a value from BIO_write_ex() less than the
amount requested or if the buffer is full request a retry. BIO_ctrl_get_write_guarantee() is a function whereas
BIO_get_write_guarantee() is a macro.
BIO_get_read_request() and BIO_ctrl_get_read_request() return the amount of data requested, or the buffer size if
it is less, if the last read attempt at the other half of the BIO pair failed due to an empty buffer. This can
be used to determine how much data should be written to the BIO so the next read will succeed: this is most
useful in TLS/SSL applications where the amount of data read is usually meaningful rather than just a buffer
size. After a successful read this call will return zero. It also will return zero once new data has been
written satisfying the read request or part of it. Note that BIO_get_read_request() never returns an amount
larger than that returned by BIO_get_write_guarantee().
BIO_ctrl_reset_read_request() can also be used to reset the value returned by BIO_get_read_request() to zero.
NOTES
Both halves of a BIO pair should be freed. That is even if one half is implicit freed due to a BIO_free_all() or
SSL_free() call the other half needs to be freed.
When used in bidirectional applications (such as TLS/SSL) care should be taken to flush any data in the write
buffer. This can be done by calling BIO_pending() on the other half of the pair and, if any data is pending,
reading it and sending it to the underlying transport. This must be done before any normal processing (such as
calling select() ) due to a request and BIO_should_read() being true.
To see why this is important consider a case where a request is sent using BIO_write_ex() and a response read
with BIO_read_ex(), this can occur during an TLS/SSL handshake for example. BIO_write_ex() will succeed and place
data in the write buffer. BIO_read_ex() will initially fail and BIO_should_read() will be true. If the
application then waits for data to be available on the underlying transport before flushing the write buffer it
will never succeed because the request was never sent!
BIO_eof() is true if no data is in the peer BIO and the peer BIO has been shutdown.
BIO_make_bio_pair(), BIO_destroy_bio_pair(), BIO_shutdown_wr(), BIO_set_write_buf_size(),
BIO_get_write_buf_size(), BIO_get_write_guarantee(), and BIO_get_read_request() are implemented as macros.
RETURN VALUES
BIO_new_bio_pair() returns 1 on success, with the new BIOs available in bio1 and bio2, or 0 on failure, with NULL
pointers stored into the locations for bio1 and bio2. Check the error stack for more information.
[XXXXX: More return values need to be added here]
EXAMPLES
The BIO pair can be used to have full control over the network access of an application. The application can call
select() on the socket as required without having to go through the SSL-interface.
BIO *internal_bio, *network_bio;
...
BIO_new_bio_pair(&internal_bio, 0, &network_bio, 0);
SSL_set_bio(ssl, internal_bio, internal_bio);
SSL_operations(); /* e.g. SSL_read and SSL_write */
...
application | TLS-engine
| |
+----------> SSL_operations()
| /\ ||
| || \/
| BIO-pair (internal_bio)
| BIO-pair (network_bio)
| || /\
| \/ ||
+-----------< BIO_operations()
| |
| |
socket
...
SSL_free(ssl); /* implicitly frees internal_bio */
BIO_free(network_bio);
...
As the BIO pair will only buffer the data and never directly access the connection, it behaves nonblocking and
will return as soon as the write buffer is full or the read buffer is drained. Then the application has to flush
the write buffer and/or fill the read buffer.
Use the BIO_ctrl_pending(), to find out whether data is buffered in the BIO and must be transferred to the
network. Use BIO_ctrl_get_read_request() to find out, how many bytes must be written into the buffer before the
SSL_operation() can successfully be continued.
WARNINGS
As the data is buffered, SSL_operation() may return with an ERROR_SSL_WANT_READ condition, but there is still
data in the write buffer. An application must not rely on the error value of SSL_operation() but must assure that
the write buffer is always flushed first. Otherwise a deadlock may occur as the peer might be waiting for the
data before being able to continue.
SEE ALSO
SSL_set_bio(3), ssl(7), bio(7), BIO_should_retry(3), BIO_read_ex(3)
COPYRIGHT
Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the
License. You can obtain a copy in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.
3.1.3 2023-09-19 BIO_S_BIO(3ossl)