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<?xml version="1.0" ?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <title>BIO_push</title> <meta http-equiv="content-type" content="text/html; charset=utf-8" /> <link rev="made" href="mailto:root@localhost" /> </head> <body> <ul id="index"> <li><a href="#NAME">NAME</a></li> <li><a href="#SYNOPSIS">SYNOPSIS</a></li> <li><a href="#DESCRIPTION">DESCRIPTION</a></li> <li><a href="#NOTES">NOTES</a></li> <li><a href="#RETURN-VALUES">RETURN VALUES</a></li> <li><a href="#EXAMPLES">EXAMPLES</a></li> <li><a href="#SEE-ALSO">SEE ALSO</a></li> <li><a href="#HISTORY">HISTORY</a></li> <li><a href="#COPYRIGHT">COPYRIGHT</a></li> </ul> <h1 id="NAME">NAME</h1> <p>BIO_push, BIO_pop, BIO_set_next - add and remove BIOs from a chain</p> <h1 id="SYNOPSIS">SYNOPSIS</h1> <pre><code> #include <openssl/bio.h> BIO *BIO_push(BIO *b, BIO *next); BIO *BIO_pop(BIO *b); void BIO_set_next(BIO *b, BIO *next);</code></pre> <h1 id="DESCRIPTION">DESCRIPTION</h1> <p>BIO_push() pushes <i>b</i> on <i>next</i>. If <i>b</i> is NULL the function does nothing and returns <i>next</i>. Otherwise it prepends <i>b</i>, which may be a single BIO or a chain of BIOs, to <i>next</i> (unless <i>next</i> is NULL). It then makes a control call on <i>b</i> and returns <i>b</i>.</p> <p>BIO_pop() removes the BIO <i>b</i> from any chain is is part of. If <i>b</i> is NULL the function does nothing and returns NULL. Otherwise it makes a control call on <i>b</i> and returns the next BIO in the chain, or NULL if there is no next BIO. The removed BIO becomes a single BIO with no association with the original chain, it can thus be freed or be made part of a different chain.</p> <p>BIO_set_next() replaces the existing next BIO in a chain with the BIO pointed to by <i>next</i>. The new chain may include some of the same BIOs from the old chain or it may be completely different.</p> <h1 id="NOTES">NOTES</h1> <p>The names of these functions are perhaps a little misleading. BIO_push() joins two BIO chains whereas BIO_pop() deletes a single BIO from a chain, the deleted BIO does not need to be at the end of a chain.</p> <p>The process of calling BIO_push() and BIO_pop() on a BIO may have additional consequences (a control call is made to the affected BIOs). Any effects will be noted in the descriptions of individual BIOs.</p> <h1 id="RETURN-VALUES">RETURN VALUES</h1> <p>BIO_push() returns the head of the chain, which usually is <i>b</i>, or <i>next</i> if <i>b</i> is NULL.</p> <p>BIO_pop() returns the next BIO in the chain, or NULL if there is no next BIO.</p> <h1 id="EXAMPLES">EXAMPLES</h1> <p>For these examples suppose <i>md1</i> and <i>md2</i> are digest BIOs, <i>b64</i> is a base64 BIO and <i>f</i> is a file BIO.</p> <p>If the call:</p> <pre><code> BIO_push(b64, f);</code></pre> <p>is made then the new chain will be <i>b64-f</i>. After making the calls</p> <pre><code> BIO_push(md2, b64); BIO_push(md1, md2);</code></pre> <p>the new chain is <i>md1-md2-b64-f</i>. Data written to <i>md1</i> will be digested by <i>md1</i> and <i>md2</i>, base64 encoded, and finally written to <i>f</i>.</p> <p>It should be noted that reading causes data to pass in the reverse direction, that is data is read from <i>f</i>, base64 decoded, and digested by <i>md2</i> and then <i>md1</i>.</p> <p>The call:</p> <pre><code> BIO_pop(md2);</code></pre> <p>will return <i>b64</i> and the new chain will be <i>md1-b64-f</i>. Data can be written to and read from <i>md1</i> as before, except that <i>md2</i> will no more be applied.</p> <h1 id="SEE-ALSO">SEE ALSO</h1> <p><a href="/../man7/bio.html">bio</a></p> <h1 id="HISTORY">HISTORY</h1> <p>The BIO_set_next() function was added in OpenSSL 1.1.0.</p> <h1 id="COPYRIGHT">COPYRIGHT</h1> <p>Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.</p> <p>Licensed under the OpenSSL license (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <a href="https://www.openssl.org/source/license.html">https://www.openssl.org/source/license.html</a>.</p> </body> </html>