99 lines
2.8 KiB
Plaintext
99 lines
2.8 KiB
Plaintext
=pod
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=head1 NAME
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BIO_push, BIO_pop, BIO_set_next - add and remove BIOs from a chain
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=head1 SYNOPSIS
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#include <openssl/bio.h>
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BIO *BIO_push(BIO *b, BIO *next);
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BIO *BIO_pop(BIO *b);
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void BIO_set_next(BIO *b, BIO *next);
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=head1 DESCRIPTION
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BIO_push() pushes I<b> on I<next>.
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If I<b> is NULL the function does nothing and returns I<next>.
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Otherwise it prepends I<b>, which may be a single BIO or a chain of BIOs,
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to I<next> (unless I<next> is NULL).
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It then makes a control call on I<b> and returns I<b>.
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BIO_pop() removes the BIO I<b> from any chain is is part of.
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If I<b> is NULL the function does nothing and returns NULL.
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Otherwise it makes a control call on I<b> and
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returns the next BIO in the chain, or NULL if there is no next BIO.
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The removed BIO becomes a single BIO with no association with
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the original chain, it can thus be freed or be made part of a different chain.
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BIO_set_next() replaces the existing next BIO in a chain with the BIO pointed to
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by I<next>. The new chain may include some of the same BIOs from the old chain
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or it may be completely different.
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=head1 NOTES
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The names of these functions are perhaps a little misleading. BIO_push()
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joins two BIO chains whereas BIO_pop() deletes a single BIO from a chain,
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the deleted BIO does not need to be at the end of a chain.
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The process of calling BIO_push() and BIO_pop() on a BIO may have additional
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consequences (a control call is made to the affected BIOs).
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Any effects will be noted in the descriptions of individual BIOs.
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=head1 RETURN VALUES
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BIO_push() returns the head of the chain,
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which usually is I<b>, or I<next> if I<b> is NULL.
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BIO_pop() returns the next BIO in the chain,
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or NULL if there is no next BIO.
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=head1 EXAMPLES
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For these examples suppose I<md1> and I<md2> are digest BIOs,
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I<b64> is a base64 BIO and I<f> is a file BIO.
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If the call:
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BIO_push(b64, f);
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is made then the new chain will be I<b64-f>. After making the calls
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BIO_push(md2, b64);
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BIO_push(md1, md2);
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the new chain is I<md1-md2-b64-f>. Data written to I<md1> will be digested
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by I<md1> and I<md2>, base64 encoded, and finally written to I<f>.
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It should be noted that reading causes data to pass in the reverse
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direction, that is data is read from I<f>, base64 decoded,
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and digested by I<md2> and then I<md1>.
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The call:
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BIO_pop(md2);
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will return I<b64> and the new chain will be I<md1-b64-f>.
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Data can be written to and read from I<md1> as before,
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except that I<md2> will no more be applied.
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=head1 SEE ALSO
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L<bio>
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=head1 HISTORY
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The BIO_set_next() function was added in OpenSSL 1.1.0.
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=head1 COPYRIGHT
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Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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