1.\" $OpenBSD: SSL_CTX_set_msg_callback.3,v 1.2 2016/12/01 15:26:11 schwarze Exp $ 2.\" OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100 3.\" 4.\" This file was written by Bodo Moeller <bodo@openssl.org>. 5.\" Copyright (c) 2001, 2014, 2016 The OpenSSL Project. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in 16.\" the documentation and/or other materials provided with the 17.\" distribution. 18.\" 19.\" 3. 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IN NO EVENT SHALL THE OpenSSL PROJECT OR 42.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 43.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 44.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 45.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 46.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 47.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 48.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED 49.\" OF THE POSSIBILITY OF SUCH DAMAGE. 50.\" 51.Dd $Mdocdate: December 1 2016 $ 52.Dt SSL_CTX_SET_MSG_CALLBACK 3 53.Os 54.Sh NAME 55.Nm SSL_CTX_set_msg_callback , 56.Nm SSL_CTX_set_msg_callback_arg , 57.Nm SSL_set_msg_callback , 58.Nm SSL_set_msg_callback_arg 59.Nd install callback for observing protocol messages 60.Sh SYNOPSIS 61.In openssl/ssl.h 62.Ft void 63.Fo SSL_CTX_set_msg_callback 64.Fa "SSL_CTX *ctx" 65.Fa "void (*cb)(int write_p, int version, int content_type, const void *buf, size_t len, SSL *ssl, void *arg)" 66.Fc 67.Ft void 68.Fn SSL_CTX_set_msg_callback_arg "SSL_CTX *ctx" "void *arg" 69.Ft void 70.Fo SSL_set_msg_callback 71.Fa "SSL *ssl" 72.Fa "void (*cb)(int write_p, int version, int content_type, const void *buf, size_t len, SSL *ssl, void *arg)" 73.Fc 74.Ft void 75.Fn SSL_set_msg_callback_arg "SSL *ssl" "void *arg" 76.Sh DESCRIPTION 77.Fn SSL_CTX_set_msg_callback 78or 79.Fn SSL_set_msg_callback 80can be used to define a message callback function 81.Fa cb 82for observing all SSL/TLS protocol messages (such as handshake messages) 83that are received or sent. 84.Fn SSL_CTX_set_msg_callback_arg 85and 86.Fn SSL_set_msg_callback_arg 87can be used to set argument 88.Fa arg 89to the callback function, which is available for arbitrary application use. 90.Pp 91.Fn SSL_CTX_set_msg_callback 92and 93.Fn SSL_CTX_set_msg_callback_arg 94specify default settings that will be copied to new 95.Vt SSL 96objects by 97.Xr SSL_new 3 . 98.Fn SSL_set_msg_callback 99and 100.Fn SSL_set_msg_callback_arg 101modify the actual settings of an 102.Vt SSL 103object. 104Using a 105.Dv NULL 106pointer for 107.Fa cb 108disables the message callback. 109.Pp 110When 111.Fa cb 112is called by the SSL/TLS library for a protocol message, 113the function arguments have the following meaning: 114.Bl -tag -width Ds 115.It Fa write_p 116This flag is 0 when a protocol message has been received and 1 when a protocol 117message has been sent. 118.It Fa version 119The protocol version according to which the protocol message is 120interpreted by the library. 121Currently, this is one of 122.Dv SSL2_VERSION , 123.Dv SSL3_VERSION 124and 125.Dv TLS1_VERSION 126(for SSL 2.0, SSL 3.0 and TLS 1.0, respectively). 127.It Fa content_type 128In the case of SSL 2.0, this is always 0. 129In the case of SSL 3.0 or TLS 1.0, this is one of the 130.Em ContentType 131values defined in the protocol specification 132.Po 133.Dq change_cipher_spec(20) , 134.Dq alert(21) , 135.Dq handshake(22) ; 136but never 137.Dq application_data(23) 138because the callback will only be called for protocol messages. 139.Pc 140.It Fa buf , Fa len 141.Fa buf 142points to a buffer containing the protocol message, which consists of 143.Fa len 144bytes. 145The buffer is no longer valid after the callback function has returned. 146.It Fa ssl 147The 148.Vt SSL 149object that received or sent the message. 150.It Fa arg 151The user-defined argument optionally defined by 152.Fn SSL_CTX_set_msg_callback_arg 153or 154.Fn SSL_set_msg_callback_arg . 155.El 156.Pp 157Protocol messages are passed to the callback function after decryption 158and fragment collection where applicable. 159(Thus record boundaries are not visible.) 160.Pp 161If processing a received protocol message results in an error, 162the callback function may not be called. 163For example, the callback function will never see messages that are considered 164too large to be processed. 165.Pp 166Due to automatic protocol version negotiation, 167.Fa version 168is not necessarily the protocol version used by the sender of the message: 169If a TLS 1.0 ClientHello message is received by an SSL 3.0-only server, 170.Fa version 171will be 172.Dv SSL3_VERSION . 173.Sh SEE ALSO 174.Xr ssl 3 , 175.Xr SSL_new 3 176.Sh HISTORY 177.Fn SSL_CTX_set_msg_callback , 178.Fn SSL_CTX_set_msg_callback_arg , 179.Fn SSL_set_msg_callback 180and 181.Fn SSL_set_msg_callback_arg 182were added in OpenSSL 0.9.7. 183