SSL_CTX_set_msg_callback manpage

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SSL_CTX_set_msg_callback(3)	    OpenSSL	   SSL_CTX_set_msg_callback(3)

       SSL_CTX_set_msg_callback, SSL_CTX_set_msg_callback_arg,
       SSL_set_msg_callback, SSL_get_msg_callback_arg - install callback for
       observing protocol messages

	#include <openssl/ssl.h>

	void SSL_CTX_set_msg_callback(SSL_CTX *ctx, void (*cb)(int write_p, int version, int content_type, const void *buf, size_t len, SSL *ssl, void *arg));
	void SSL_CTX_set_msg_callback_arg(SSL_CTX *ctx, void *arg);

	void SSL_set_msg_callback(SSL *ssl, void (*cb)(int write_p, int version, int content_type, const void *buf, size_t len, SSL *ssl, void *arg));
	void SSL_set_msg_callback_arg(SSL *ssl, void *arg);

       SSL_CTX_set_msg_callback() or SSL_set_msg_callback() can be used to
       define a message callback function cb for observing all SSL/TLS
       protocol messages (such as handshake messages) that are received or
       sent.  SSL_CTX_set_msg_callback_arg() and SSL_set_msg_callback_arg()
       can be used to set argument arg to the callback function, which is
       available for arbitrary application use.

       SSL_CTX_set_msg_callback() and SSL_CTX_set_msg_callback_arg() specify
       default settings that will be copied to new SSL objects by SSL_new(3).
       SSL_set_msg_callback() and SSL_set_msg_callback_arg() modify the actual
       settings of an SSL object. Using a 0 pointer for cb disables the
       message callback.

       When cb is called by the SSL/TLS library for a protocol message, the
       function arguments have the following meaning:

	   This flag is 0 when a protocol message has been received and 1 when
	   a protocol message has been sent.

	   The protocol version according to which the protocol message is
	   interpreted by the library. Currently, this is one of SSL2_VERSION,
	   SSL3_VERSION and TLS1_VERSION (for SSL 2.0, SSL 3.0 and TLS 1.0,

	   In the case of SSL 2.0, this is always 0.  In the case of SSL 3.0
	   or TLS 1.0, this is one of the ContentType values defined in the
	   protocol specification (change_cipher_spec(20), alert(21),
	   handshake(22); but never application_data(23) because the callback
	   will only be called for protocol messages).

       buf, len
	   buf points to a buffer containing the protocol message, which
	   consists of len bytes. The buffer is no longer valid after the
	   callback function has returned.

       ssl The SSL object that received or sent the message.

       arg The user-defined argument optionally defined by
	   SSL_CTX_set_msg_callback_arg() or SSL_set_msg_callback_arg().

       Protocol messages are passed to the callback function after decryption
       and fragment collection where applicable. (Thus record boundaries are
       not visible.)

       If processing a received protocol message results in an error, the
       callback function may not be called.  For example, the callback
       function will never see messages that are considered too large to be

       Due to automatic protocol version negotiation, version is not
       necessarily the protocol version used by the sender of the message: If
       a TLS 1.0 ClientHello message is received by an SSL 3.0-only server,
       version will be SSL3_VERSION.

       ssl(3), SSL_new(3)

       SSL_CTX_set_msg_callback(), SSL_CTX_set_msg_callback_arg(),
       SSL_set_msg_callback() and SSL_get_msg_callback_arg() were added in
       OpenSSL 0.9.7.

1.0.2k				  2017-01-26	   SSL_CTX_set_msg_callback(3)