237 lines
7.4 KiB
Groff
237 lines
7.4 KiB
Groff
.\" $NetBSD: BIO_new_bio_pair.3,v 1.2 2002/02/07 07:00:37 ross Exp $
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.\" Thu Apr 12 19:26:40 2001
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.\" ======================================================================
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.\"
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.IX Title "BIO_new_bio_pair 3"
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.TH BIO_new_bio_pair 3 "0.9.6a" "2001-04-12" "OpenSSL"
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.UC
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.SH "NAME"
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BIO_new_bio_pair \- create a new \s-1BIO\s0 pair
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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 \*[Lt]openssl/bio.h\*[Gt]
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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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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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\&\fIBIO_new_bio_pair()\fR creates a buffering \s-1BIO\s0 pair. It has two endpoints between
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data can be buffered. Its typical use is to connect one endpoint as underlying
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input/output \s-1BIO\s0 to an \s-1SSL\s0 and access the other one controlled by the program
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instead of accessing the network connection directly.
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.PP
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The two new BIOs \fBbio1\fR and \fBbio2\fR are symmetric with respect to their
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functionality. The size of their buffers is determined by \fBwritebuf1\fR and
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\&\fBwritebuf2\fR. If the size give is 0, the default size is used.
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.PP
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\&\fIBIO_new_bio_pair()\fR does not check whether \fBbio1\fR or \fBbio2\fR do point to
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some other \s-1BIO\s0, the values are overwritten, \fIBIO_free()\fR is not called.
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.PP
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The two BIOs, even though forming a \s-1BIO\s0 pair and must be \fIBIO_free()\fR'ed
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separately. This can be of importance, as some SSL-functions like \fISSL_set_bio()\fR
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or \fISSL_free()\fR call \fIBIO_free()\fR implicitly, so that the peer-BIO is left
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untouched and must also be \fIBIO_free()\fR'ed.
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.SH "EXAMPLE"
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.IX Header "EXAMPLE"
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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 \fIselect()\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 6
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\& BIO *internal_bio, *network_bio;
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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);
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\& SSL_operations();
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\& ...
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.Ve
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.Vb 9
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\& application | TLS-engine
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\& | |
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\& +----------\*[Gt] SSL_operations()
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\& | /\e ||
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\& | || \e/
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\& | BIO-pair (internal_bio)
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\& +----------\*[Lt] BIO-pair (network_bio)
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\& | |
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\& socket |
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.Ve
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.Vb 4
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\& ...
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\& SSL_free(ssl); /* implicitly frees internal_bio */
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\& BIO_free(network_bio);
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\& ...
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.Ve
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As the \s-1BIO\s0 pair will only buffer the data and never directly access the
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connection, it behaves non-blocking and will return as soon as the write
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buffer is full or the read buffer is drained. Then the application has to
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flush the write buffer and/or fill the read buffer.
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.PP
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Use the \fIBIO_ctrl_pending()\fR, to find out whether data is buffered in the \s-1BIO\s0
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and must be transfered to the network. Use \fIBIO_ctrl_get_read_request()\fR to
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find out, how many bytes must be written into the buffer before the
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\&\fISSL_operation()\fR can successfully be continued.
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.SH "IMPORTANT"
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.IX Header "IMPORTANT"
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As the data is buffered, \fISSL_operation()\fR may return with a \s-1ERROR_SSL_WANT_READ\s0
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condition, but there is still data in the write buffer. An application must
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not rely on the error value of \fISSL_operation()\fR but must assure that the
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write buffer is always flushed first. Otherwise a deadlock may occur as
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the peer might be waiting for the data before being able to continue.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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The following return values can occur:
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.Ip "1" 4
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.IX Item "1"
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The \s-1BIO\s0 pair was created successfully. The new BIOs are available in
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\&\fBbio1\fR and \fBbio2\fR.
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.Ip "0" 4
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The operation failed. The \s-1NULL\s0 pointer is stored into the locations for
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\&\fBbio1\fR and \fBbio2\fR. Check the error stack for more information.
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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_ctrl_pending(3),
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BIO_ctrl_get_read_request(3)
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