1.\" $OpenBSD: BIO_push.3,v 1.7 2018/03/27 17:35:50 schwarze Exp $ 2.\" OpenSSL doc/man3/BIO_push.pod 76ed5a42 Jun 29 13:38:55 2014 +0100 3.\" OpenSSL doc/man7/bio.pod a9c85cea Nov 11 09:33:55 2016 +0100 4.\" 5.\" This file was written by Dr. Stephen Henson <steve@openssl.org>. 6.\" Copyright (c) 2000, 2014 The OpenSSL Project. All rights reserved. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 15.\" 2. Redistributions in binary form must reproduce the above copyright 16.\" notice, this list of conditions and the following disclaimer in 17.\" the documentation and/or other materials provided with the 18.\" distribution. 19.\" 20.\" 3. All advertising materials mentioning features or use of this 21.\" software must display the following acknowledgment: 22.\" "This product includes software developed by the OpenSSL Project 23.\" for use in the OpenSSL Toolkit. (http://www.openssl.org/)" 24.\" 25.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to 26.\" endorse or promote products derived from this software without 27.\" prior written permission. For written permission, please contact 28.\" openssl-core@openssl.org. 29.\" 30.\" 5. Products derived from this software may not be called "OpenSSL" 31.\" nor may "OpenSSL" appear in their names without prior written 32.\" permission of the OpenSSL Project. 33.\" 34.\" 6. Redistributions of any form whatsoever must retain the following 35.\" acknowledgment: 36.\" "This product includes software developed by the OpenSSL Project 37.\" for use in the OpenSSL Toolkit (http://www.openssl.org/)" 38.\" 39.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY 40.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 41.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 42.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR 43.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 44.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 45.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 46.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 47.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 48.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 49.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED 50.\" OF THE POSSIBILITY OF SUCH DAMAGE. 51.\" 52.Dd $Mdocdate: March 27 2018 $ 53.Dt BIO_PUSH 3 54.Os 55.Sh NAME 56.Nm BIO_push , 57.Nm BIO_pop 58.Nd add and remove BIOs from a chain 59.Sh SYNOPSIS 60.In openssl/bio.h 61.Ft BIO * 62.Fo BIO_push 63.Fa "BIO *b" 64.Fa "BIO *append" 65.Fc 66.Ft BIO * 67.Fo BIO_pop 68.Fa "BIO *b" 69.Fc 70.Sh DESCRIPTION 71BIOs can be joined together to form chains. 72A chain normally consist of one or more filter BIOs 73and one source/sink BIO at the end. 74Data read from or written to the first BIO traverses the chain 75to the end. 76A single BIO can be regarded as a chain with one component. 77.Pp 78The 79.Fn BIO_push 80function appends the BIO 81.Fa append 82to 83.Fa b 84and returns 85.Fa b . 86.Pp 87.Fn BIO_pop 88removes the BIO 89.Fa b 90from a chain and returns the next BIO in the chain, or 91.Dv NULL 92if there is no next BIO. 93The removed BIO then becomes a single BIO with no association with the 94original chain. 95it can thus be freed or attached to a different chain. 96.Pp 97The names of these functions are perhaps a little misleading. 98.Fn BIO_push 99joins two BIO chains whereas 100.Fn BIO_pop 101deletes a single BIO from a chain; 102the deleted BIO does not need to be at the end of a chain. 103.Pp 104The process of calling 105.Fn BIO_push 106and 107.Fn BIO_pop 108on a BIO may have additional consequences: a 109.Xr BIO_ctrl 3 110call is made to the affected BIOs. 111Any effects will be noted in the descriptions of individual BIOs. 112.Sh RETURN VALUES 113.Fn BIO_push 114returns the beginning of the chain, 115.Fa b . 116.Pp 117.Fn BIO_pop 118returns the next BIO in the chain, or 119.Dv NULL 120if there is no next BIO. 121.Sh EXAMPLES 122For these examples suppose 123.Sy md1 124and 125.Sy md2 126are digest BIOs, 127.Sy b64 128is a Base64 BIO and 129.Sy f 130is a file BIO. 131.Pp 132If the call 133.Pp 134.Dl BIO_push(b64, f); 135.Pp 136is made then the new chain will be 137.Sy b64-f . 138After making the calls 139.Bd -literal -offset indent 140BIO_push(md2, b64); 141BIO_push(md1, md2); 142.Ed 143.Pp 144the new chain is 145.Sy md1-md2-b64-f . 146Data written to 147.Sy md1 148will be digested 149by 150.Sy md1 151and 152.Sy md2 , 153Base64-encoded and written to 154.Sy f . 155.Pp 156It should be noted that reading causes data to pass 157in the reverse direction. 158That is, data is read from 159.Sy f , 160Base64-decoded and digested by 161.Sy md1 162and 163.Sy md2 . 164If this call is made: 165.Pp 166.Dl BIO_pop(md2); 167.Pp 168The call will return 169.Sy b64 170and the new chain will be 171.Sy md1-b64-f ; 172data can be written to 173.Sy md1 174as before. 175.Sh SEE ALSO 176.Xr BIO_find_type 3 , 177.Xr BIO_new 3 , 178.Xr BIO_read 3 179.Sh HISTORY 180.Fn BIO_push 181first appeared in SSLeay 0.6.0. 182.Fn BIO_pop 183first appeared in SSLeay 0.6.4. 184Both functions have been available since 185.Ox 2.4 . 186