SSL_CTX_SET_INFO_CALLBACK

Section: OpenSSL (3)
Updated: 2021-03-26
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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

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));
         }
     }
 }

COPYRIGHT

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>.