103 lines
3.3 KiB
Text
103 lines
3.3 KiB
Text
=pod
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=head1 NAME
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BIO_new_bio_pair - create a new BIO pair
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=head1 SYNOPSIS
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#include <openssl/bio.h>
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int BIO_new_bio_pair(BIO **bio1, size_t writebuf1, BIO **bio2, size_t writebuf2);
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=head1 DESCRIPTION
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BIO_new_bio_pair() creates a buffering BIO pair based on the
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L<SSL_set_bio(3)|SSL_set_bio(3)> method. The BIO pair has two endpoints between which
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data can be buffered. Its typical use is to connect one endpoint as underlying
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input/output BIO to an SSL and access the other one controlled by the program
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instead of accessing the network connection directly.
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The two new BIOs B<bio1> and B<bio2> are symmetric with respect to their
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functionality. The size of their buffers is determined by B<writebuf1> and
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B<writebuf2>. If the size give is 0, the default size is used.
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BIO_new_bio_pair() does not check whether B<bio1> or B<bio2> do point to
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some other BIO, the values are overwritten, BIO_free() is not called.
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The two BIOs, even though forming a BIO pair and must be BIO_free()'ed
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separately. This can be of importance, as some SSL-functions like SSL_set_bio()
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or SSL_free() call BIO_free() implicitly, so that the peer-BIO is left
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untouched and must also be BIO_free()'ed.
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=head1 EXAMPLE
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The BIO pair can be used to have full control over the network access of an
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application. The application can call select() on the socket as required
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without having to go through the SSL-interface.
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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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application | TLS-engine
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+----------> SSL_operations()
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| /\ ||
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| BIO-pair (internal_bio)
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+----------< BIO-pair (network_bio)
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socket |
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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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As the BIO 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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Use the BIO_ctrl_pending(), to find out whether data is buffered in the BIO
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and must be transfered to the network. Use BIO_ctrl_get_read_request() to
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find out, how many bytes must be written into the buffer before the
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SSL_operation() can successfully be continued.
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=head1 IMPORTANT
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As the data is buffered, SSL_operation() may return with a ERROR_SSL_WANT_READ
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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 SSL_operation() 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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=head1 RETURN VALUES
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The following return values can occur:
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=over 4
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=item 1
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The BIO pair was created successfully. The new BIOs are available in
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B<bio1> and B<bio2>.
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=item 0
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The operation failed. The NULL pointer is stored into the locations for
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B<bio1> and B<bio2>. Check the error stack for more information.
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=back
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=head1 SEE ALSO
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L<SSL_set_bio(3)|SSL_set_bio(3)>, L<ssl(3)|ssl(3)>, L<bio(3)|bio(3)>,
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L<BIO_ctrl_pending(3)|BIO_ctrl_pending(3)>,
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L<BIO_ctrl_get_read_request(3)|BIO_ctrl_get_read_request(3)>
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=cut
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