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SSL_CTX_SET_INFO_CALLBACK(3) Library Functions Manual SSL_CTX_SET_INFO_CALLBACK(3)

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

#include <openssl/ssl.h>
void
SSL_CTX_set_info_callback(SSL_CTX *ctx, void (*callback)(const SSL *ssl, int where, int ret));
void
(*SSL_CTX_get_info_callback(const SSL_CTX *ctx))(const SSL *ssl, int where, int ret);
void
SSL_set_info_callback(SSL *ssl, void (*callback)(const SSL *ssl, int where, int ret));
void
(*SSL_get_info_callback(const SSL *ssl))(const SSL *ssl, int where, int ret);

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.
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 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 bitmask made up of the following bits:
 
 
Callback has been called to indicate state change inside a loop.
 
 
Callback has been called to indicate error exit of a handshake function. (May be soft error with retry option for non-blocking setups.)
 
 
Callback has been called during read operation.
 
 
Callback has been called during write operation.
 
 
Callback has been called due to an alert being sent or received.
 
 
 
 
 
 
 
 
Callback has been called because a new handshake is started.
 
 
Callback has been called because a handshake is finished.
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.

SSL_CTX_get_info_callback() and SSL_get_info_callback() return a pointer to the current callback or NULL if none is set.

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; 
 
	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)); 
		} 
	} 
}

ssl(3), SSL_alert_type_string(3), SSL_state_string(3)

These functions first appeared in SSLeay 0.6.0 and have been available since OpenBSD 2.4.
March 27, 2018 OpenBSD-current