277 lines
10 KiB
Groff
277 lines
10 KiB
Groff
.\" $NetBSD: BIO_s_bio.3,v 1.6 2002/08/09 16:15:37 itojun Exp $
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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 "0.9.6g" "2001-04-12" "OpenSSL"
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.UC
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.SH "NAME"
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BIO_s_bio, BIO_make_bio_pair, BIO_destroy_bio_pair, BIO_shutdown_wr,
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BIO_set_write_buf_size, BIO_get_write_buf_size, BIO_new_bio_pair,
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BIO_get_write_guarantee, BIO_ctrl_get_write_guarantee, BIO_get_read_request,
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BIO_ctrl_get_read_request, BIO_ctrl_reset_read_request \- \s-1BIO\s0 pair \s-1BIO\s0
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.SH "LIBRARY"
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libcrypto, -lcrypto
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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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.Ve
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.Vb 1
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\& BIO_METHOD *BIO_s_bio(void);
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.Ve
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.Vb 2
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\& #define BIO_make_bio_pair(b1,b2) (int)BIO_ctrl(b1,BIO_C_MAKE_BIO_PAIR,0,b2)
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\& #define BIO_destroy_bio_pair(b) (int)BIO_ctrl(b,BIO_C_DESTROY_BIO_PAIR,0,NULL)
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.Ve
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.Vb 1
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\& #define BIO_shutdown_wr(b) (int)BIO_ctrl(b, BIO_C_SHUTDOWN_WR, 0, NULL)
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.Ve
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.Vb 2
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\& #define BIO_set_write_buf_size(b,size) (int)BIO_ctrl(b,BIO_C_SET_WRITE_BUF_SIZE,size,NULL)
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\& #define BIO_get_write_buf_size(b,size) (size_t)BIO_ctrl(b,BIO_C_GET_WRITE_BUF_SIZE,size,NULL)
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.Ve
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.Vb 1
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\& int BIO_new_bio_pair(BIO **bio1, size_t writebuf1, BIO **bio2, size_t writebuf2);
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.Ve
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.Vb 2
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\& #define BIO_get_write_guarantee(b) (int)BIO_ctrl(b,BIO_C_GET_WRITE_GUARANTEE,0,NULL)
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\& size_t BIO_ctrl_get_write_guarantee(BIO *b);
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.Ve
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.Vb 2
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\& #define BIO_get_read_request(b) (int)BIO_ctrl(b,BIO_C_GET_READ_REQUEST,0,NULL)
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\& size_t BIO_ctrl_get_read_request(BIO *b);
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.Ve
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.Vb 1
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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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\&\fIBIO_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\s0 I/O 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 \fIBIO_read()\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 \fIBIO_write()\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 \fIBIO_ctrl_pending()\fR and \fIBIO_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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\&\fIBIO_reset()\fR clears any data in the write buffer.
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.PP
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\&\fIBIO_make_bio_pair()\fR joins two separate BIOs into a connected pair.
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.PP
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\&\fIBIO_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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\&\fIBIO_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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\&\fIBIO_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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\&\fIBIO_get_write_buf_size()\fR returns the size of the write buffer.
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.PP
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\&\fIBIO_new_bio_pair()\fR combines the calls to \fIBIO_new()\fR, \fIBIO_make_bio_pair()\fR and
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\&\fIBIO_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.
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.PP
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\&\fIBIO_get_write_guarantee()\fR and \fIBIO_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 \fIBIO_write()\fR less than the amount requested or if the
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buffer is full request a retry. \fIBIO_ctrl_get_write_guarantee()\fR is a function
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whereas \fIBIO_get_write_guarantee()\fR is a macro.
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.PP
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\&\fIBIO_get_read_request()\fR and \fIBIO_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 \fIBIO_get_read_request()\fR never returns an amount larger
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than that returned by \fIBIO_get_write_guarantee()\fR.
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.PP
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\&\fIBIO_ctrl_reset_read_request()\fR can also be used to reset the value returned by
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\&\fIBIO_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 \fIBIO_free_all()\fR or \fISSL_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 \fIBIO_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 \fIselect()\fR ) due to a request and \fIBIO_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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\&\fIBIO_write()\fR and a response read with \fIBIO_read()\fR, this can occur during an
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\&\s-1TLS/SSL\s0 handshake for example. \fIBIO_write()\fR will succeed and place data in the write
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buffer. \fIBIO_read()\fR will initially fail and \fIBIO_should_read()\fR will be true. If
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the application then waits for data to be available on the underlying transport
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before flushing the write buffer it will never succeed because the request was
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never sent!
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.SH "EXAMPLE"
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.IX Header "EXAMPLE"
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\&\s-1TBA\s0
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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SSL_set_bio(3), ssl(3), openssl_bio(3),
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BIO_should_retry(3), BIO_read(3)
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