forked from cory/tildefriends
330 lines
13 KiB
Groff
330 lines
13 KiB
Groff
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.\" ========================================================================
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.\"
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.IX Title "BIO_S_BIO 3"
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.TH BIO_S_BIO 3 "2020-04-21" "1.1.1g" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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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
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/bio.h>
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\&
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\& const BIO_METHOD *BIO_s_bio(void);
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\&
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\& int BIO_make_bio_pair(BIO *b1, BIO *b2);
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\& int BIO_destroy_bio_pair(BIO *b);
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\& int BIO_shutdown_wr(BIO *b);
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\&
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\& int BIO_set_write_buf_size(BIO *b, long size);
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\& size_t BIO_get_write_buf_size(BIO *b, long size);
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\&
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\& int BIO_new_bio_pair(BIO **bio1, size_t writebuf1, BIO **bio2, size_t writebuf2);
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\&
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\& int BIO_get_write_guarantee(BIO *b);
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\& size_t BIO_ctrl_get_write_guarantee(BIO *b);
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\& int BIO_get_read_request(BIO *b);
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\& size_t BIO_ctrl_get_read_request(BIO *b);
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\& int BIO_ctrl_reset_read_request(BIO *b);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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\&\fBBIO_s_bio()\fR returns the method for a \s-1BIO\s0 pair. A \s-1BIO\s0 pair is a pair of source/sink
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BIOs where data written to either half of the pair is buffered and can be read from
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the other half. Both halves must usually by handled by the same application thread
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since no locking is done on the internal data structures.
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.PP
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Since \s-1BIO\s0 chains typically end in a source/sink \s-1BIO\s0 it is possible to make this
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one half of a \s-1BIO\s0 pair and have all the data processed by the chain under application
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control.
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.PP
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One typical use of \s-1BIO\s0 pairs is to place \s-1TLS/SSL I/O\s0 under application control, this
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can be used when the application wishes to use a non standard transport for
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\&\s-1TLS/SSL\s0 or the normal socket routines are inappropriate.
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.PP
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Calls to \fBBIO_read_ex()\fR will read data from the buffer or request a retry if no
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data is available.
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.PP
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Calls to \fBBIO_write_ex()\fR will place data in the buffer or request a retry if the
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buffer is full.
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.PP
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The standard calls \fBBIO_ctrl_pending()\fR and \fBBIO_ctrl_wpending()\fR can be used to
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determine the amount of pending data in the read or write buffer.
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.PP
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\&\fBBIO_reset()\fR clears any data in the write buffer.
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.PP
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\&\fBBIO_make_bio_pair()\fR joins two separate BIOs into a connected pair.
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.PP
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\&\fBBIO_destroy_pair()\fR destroys the association between two connected BIOs. Freeing
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up any half of the pair will automatically destroy the association.
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.PP
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\&\fBBIO_shutdown_wr()\fR is used to close down a \s-1BIO\s0 \fBb\fR. After this call no further
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writes on \s-1BIO\s0 \fBb\fR are allowed (they will return an error). Reads on the other
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half of the pair will return any pending data or \s-1EOF\s0 when all pending data has
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been read.
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.PP
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\&\fBBIO_set_write_buf_size()\fR sets the write buffer size of \s-1BIO\s0 \fBb\fR to \fBsize\fR.
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If the size is not initialized a default value is used. This is currently
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17K, sufficient for a maximum size \s-1TLS\s0 record.
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.PP
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\&\fBBIO_get_write_buf_size()\fR returns the size of the write buffer.
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.PP
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\&\fBBIO_new_bio_pair()\fR combines the calls to \fBBIO_new()\fR, \fBBIO_make_bio_pair()\fR and
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\&\fBBIO_set_write_buf_size()\fR to create a connected pair of BIOs \fBbio1\fR, \fBbio2\fR
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with write buffer sizes \fBwritebuf1\fR and \fBwritebuf2\fR. If either size is
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zero then the default size is used. \fBBIO_new_bio_pair()\fR does not check whether
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\&\fBbio1\fR or \fBbio2\fR do point to some other \s-1BIO,\s0 the values are overwritten,
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\&\fBBIO_free()\fR is not called.
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.PP
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\&\fBBIO_get_write_guarantee()\fR and \fBBIO_ctrl_get_write_guarantee()\fR return the maximum
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length of data that can be currently written to the \s-1BIO.\s0 Writes larger than this
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value will return a value from \fBBIO_write_ex()\fR less than the amount requested or
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if the buffer is full request a retry. \fBBIO_ctrl_get_write_guarantee()\fR is a
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function whereas \fBBIO_get_write_guarantee()\fR is a macro.
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.PP
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\&\fBBIO_get_read_request()\fR and \fBBIO_ctrl_get_read_request()\fR return the
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amount of data requested, or the buffer size if it is less, if the
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last read attempt at the other half of the \s-1BIO\s0 pair failed due to an
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empty buffer. This can be used to determine how much data should be
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written to the \s-1BIO\s0 so the next read will succeed: this is most useful
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in \s-1TLS/SSL\s0 applications where the amount of data read is usually
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meaningful rather than just a buffer size. After a successful read
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this call will return zero. It also will return zero once new data
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has been written satisfying the read request or part of it.
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Note that \fBBIO_get_read_request()\fR never returns an amount larger
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than that returned by \fBBIO_get_write_guarantee()\fR.
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.PP
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\&\fBBIO_ctrl_reset_read_request()\fR can also be used to reset the value returned by
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\&\fBBIO_get_read_request()\fR to zero.
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.SH "NOTES"
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.IX Header "NOTES"
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Both halves of a \s-1BIO\s0 pair should be freed. That is even if one half is implicit
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freed due to a \fBBIO_free_all()\fR or \fBSSL_free()\fR call the other half needs to be freed.
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.PP
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When used in bidirectional applications (such as \s-1TLS/SSL\s0) care should be taken to
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flush any data in the write buffer. This can be done by calling \fBBIO_pending()\fR
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on the other half of the pair and, if any data is pending, reading it and sending
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it to the underlying transport. This must be done before any normal processing
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(such as calling \fBselect()\fR ) due to a request and \fBBIO_should_read()\fR being true.
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.PP
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To see why this is important consider a case where a request is sent using
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\&\fBBIO_write_ex()\fR and a response read with \fBBIO_read_ex()\fR, this can occur during an
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\&\s-1TLS/SSL\s0 handshake for example. \fBBIO_write_ex()\fR will succeed and place data in the
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write buffer. \fBBIO_read_ex()\fR will initially fail and \fBBIO_should_read()\fR will be
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true. If the application then waits for data to be available on the underlying
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transport before flushing the write buffer it will never succeed because the
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request was never sent!
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.PP
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\&\fBBIO_eof()\fR is true if no data is in the peer \s-1BIO\s0 and the peer \s-1BIO\s0 has been
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shutdown.
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.PP
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\&\fBBIO_make_bio_pair()\fR, \fBBIO_destroy_bio_pair()\fR, \fBBIO_shutdown_wr()\fR,
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\&\fBBIO_set_write_buf_size()\fR, \fBBIO_get_write_buf_size()\fR,
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\&\fBBIO_get_write_guarantee()\fR, and \fBBIO_get_read_request()\fR are implemented
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as macros.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fBBIO_new_bio_pair()\fR returns 1 on success, with the new BIOs available in
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\&\fBbio1\fR and \fBbio2\fR, or 0 on failure, with \s-1NULL\s0 pointers stored into the
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locations for \fBbio1\fR and \fBbio2\fR. Check the error stack for more information.
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.PP
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[\s-1XXXXX:\s0 More return values need to be added here]
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.SH "EXAMPLES"
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.IX Header "EXAMPLES"
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The \s-1BIO\s0 pair can be used to have full control over the network access of an
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application. The application can call \fBselect()\fR on the socket as required
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without having to go through the SSL-interface.
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.PP
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.Vb 1
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\& BIO *internal_bio, *network_bio;
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\&
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\& ...
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\& BIO_new_bio_pair(&internal_bio, 0, &network_bio, 0);
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\& SSL_set_bio(ssl, internal_bio, internal_bio);
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\& SSL_operations(); /* e.g SSL_read and SSL_write */
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\& ...
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\&
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\& application | TLS\-engine
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\& | |
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\& +\-\-\-\-\-\-\-\-\-\-> SSL_operations()
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\& | /\e ||
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\& | || \e/
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\& | BIO\-pair (internal_bio)
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\& | BIO\-pair (network_bio)
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||
|
|
\& | || /\e
|
||
|
|
\& | \e/ ||
|
||
|
|
\& +\-\-\-\-\-\-\-\-\-\-\-< BIO_operations()
|
||
|
|
\& | |
|
||
|
|
\& | |
|
||
|
|
\& socket
|
||
|
|
\&
|
||
|
|
\& ...
|
||
|
|
\& SSL_free(ssl); /* implicitly frees internal_bio */
|
||
|
|
\& BIO_free(network_bio);
|
||
|
|
\& ...
|
||
|
|
.Ve
|
||
|
|
.PP
|
||
|
|
As the \s-1BIO\s0 pair will only buffer the data and never directly access the
|
||
|
|
connection, it behaves non-blocking 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.
|
||
|
|
.PP
|
||
|
|
Use the \fBBIO_ctrl_pending()\fR, to find out whether data is buffered in the \s-1BIO\s0
|
||
|
|
and must be transferred to the network. Use \fBBIO_ctrl_get_read_request()\fR to
|
||
|
|
find out, how many bytes must be written into the buffer before the
|
||
|
|
\&\fBSSL_operation()\fR can successfully be continued.
|
||
|
|
.SH "WARNINGS"
|
||
|
|
.IX Header "WARNINGS"
|
||
|
|
As the data is buffered, \fBSSL_operation()\fR may return with an \s-1ERROR_SSL_WANT_READ\s0
|
||
|
|
condition, but there is still data in the write buffer. An application must
|
||
|
|
not rely on the error value of \fBSSL_operation()\fR 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.
|
||
|
|
.SH "SEE ALSO"
|
||
|
|
.IX Header "SEE ALSO"
|
||
|
|
\&\fBSSL_set_bio\fR\|(3), \fBssl\fR\|(7), \fBbio\fR\|(7),
|
||
|
|
\&\fBBIO_should_retry\fR\|(3), \fBBIO_read_ex\fR\|(3)
|
||
|
|
.SH "COPYRIGHT"
|
||
|
|
.IX Header "COPYRIGHT"
|
||
|
|
Copyright 2000\-2019 The OpenSSL Project Authors. All Rights Reserved.
|
||
|
|
.PP
|
||
|
|
Licensed under the OpenSSL license (the \*(L"License\*(R"). You may not use
|
||
|
|
this file except in compliance with the License. You can obtain a copy
|
||
|
|
in the file \s-1LICENSE\s0 in the source distribution or at
|
||
|
|
<https://www.openssl.org/source/license.html>.
|