NAME

       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

SYNOPSIS

        #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_CTX *ctx, 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_CTX *ctx, void *arg);

DESCRIPTION

       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:

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

       version
           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, respectively).

       content_type
           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 The buffer is no
           longer valid after the callback function has returned.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().

NOTES

       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 processed.

       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.

SEE ALSO

       ssl(3), SSL_new(3)

HISTORY

       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.

1.0.1f                                             2014-01-06                     SSL_CTX_set_msg_callback(3SSL)