Updated: 2021/Apr/14


SSL_CTX_set_info_callback(3)        OpenSSL       SSL_CTX_set_info_callback(3)



NAME
       SSL_CTX_set_info_callback, SSL_CTX_get_info_callback,
       SSL_set_info_callback, SSL_get_info_callback - handle information
       callback for SSL connections

LIBRARY
       libcrypto, -lcrypto

SYNOPSIS
        #include <openssl/ssl.h>

        void SSL_CTX_set_info_callback(SSL_CTX *ctx, void (*callback)());
        void (*SSL_CTX_get_info_callback(const SSL_CTX *ctx))();

        void SSL_set_info_callback(SSL *ssl, void (*callback)());
        void (*SSL_get_info_callback(const SSL *ssl))();

DESCRIPTION
       SSL_CTX_set_info_callback() sets the callback function, that can be
       used to obtain state information for SSL objects created from ctx
       during connection setup and use. The setting for ctx is overridden from
       the setting for a specific SSL object, if specified.  When callback is
       NULL, no callback function is used.

       SSL_set_info_callback() sets the callback function, that can be used to
       obtain state information for ssl during connection setup and use.  When
       callback is NULL, the callback setting currently valid for ctx is used.

       SSL_CTX_get_info_callback() returns a pointer to the currently set
       information callback function for ctx.

       SSL_get_info_callback() returns a pointer to the currently set
       information callback function for ssl.

NOTES
       When setting up a connection and during use, it is possible to obtain
       state information from the SSL/TLS engine. When set, an information
       callback function is called whenever a significant event occurs such
       as: the state changes, an alert appears, or an error occurs.

       The callback function is called as callback(SSL *ssl, int where, int
       ret).  The where argument specifies information about where (in which
       context) the callback function was called. If ret is 0, an error
       condition occurred.  If an alert is handled, SSL_CB_ALERT is set and
       ret specifies the alert information.

       where is a bit mask made up of the following bits:

       SSL_CB_LOOP
           Callback has been called to indicate state change or some other
           significant state machine event. This may mean that the callback
           gets invoked more than once per state in some situations.

       SSL_CB_EXIT
           Callback has been called to indicate exit of a handshake function.
           This will happen after the end of a handshake, but may happen at
           other times too such as on error or when IO might otherwise block
           and nonblocking is being used.

       SSL_CB_READ
           Callback has been called during read operation.

       SSL_CB_WRITE
           Callback has been called during write operation.

       SSL_CB_ALERT
           Callback has been called due to an alert being sent or received.

       SSL_CB_READ_ALERT               (SSL_CB_ALERT|SSL_CB_READ)
       SSL_CB_WRITE_ALERT              (SSL_CB_ALERT|SSL_CB_WRITE)
       SSL_CB_ACCEPT_LOOP              (SSL_ST_ACCEPT|SSL_CB_LOOP)
       SSL_CB_ACCEPT_EXIT              (SSL_ST_ACCEPT|SSL_CB_EXIT)
       SSL_CB_CONNECT_LOOP             (SSL_ST_CONNECT|SSL_CB_LOOP)
       SSL_CB_CONNECT_EXIT             (SSL_ST_CONNECT|SSL_CB_EXIT)
       SSL_CB_HANDSHAKE_START
           Callback has been called because a new handshake is started. It
           also occurs when resuming a handshake following a pause to handle
           early data.

       SSL_CB_HANDSHAKE_DONE
           Callback has been called because a handshake is finished.  It also
           occurs if the handshake is paused to allow the exchange of early
           data.

       The current state information can be obtained using the
       SSL_state_string(3) family of functions.

       The ret information can be evaluated using the SSL_alert_type_string(3)
       family of functions.

RETURN VALUES
       SSL_set_info_callback() does not provide diagnostic information.

       SSL_get_info_callback() returns the current setting.

EXAMPLES
       The following example callback function prints state strings,
       information about alerts being handled and error messages to the
       bio_err BIO.

        void apps_ssl_info_callback(SSL *s, int where, int ret)
        {
            const char *str;
            int w = where & ~SSL_ST_MASK;

            if (w & SSL_ST_CONNECT)
                str = "SSL_connect";
            else if (w & SSL_ST_ACCEPT)
                str = "SSL_accept";
            else
                str = "undefined";

            if (where & SSL_CB_LOOP) {
                BIO_printf(bio_err, "%s:%s\n", str, SSL_state_string_long(s));
            } else if (where & SSL_CB_ALERT) {
                str = (where & SSL_CB_READ) ? "read" : "write";
                BIO_printf(bio_err, "SSL3 alert %s:%s:%s\n", str,
                           SSL_alert_type_string_long(ret),
                           SSL_alert_desc_string_long(ret));
            } else if (where & SSL_CB_EXIT) {
                if (ret == 0) {
                    BIO_printf(bio_err, "%s:failed in %s\n",
                               str, SSL_state_string_long(s));
                } else if (ret < 0) {
                    BIO_printf(bio_err, "%s:error in %s\n",
                               str, SSL_state_string_long(s));
                }
            }
        }

SEE ALSO
       ssl(7), SSL_state_string(3), SSL_alert_type_string(3)

COPYRIGHT
       Copyright 2001-2020 The OpenSSL Project Authors. All Rights Reserved.

       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
       <https://www.openssl.org/source/license.html>.



1.1.1i                            2020-12-10      SSL_CTX_set_info_callback(3)