NAME    [Toc]    [Back]

       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    [Toc]    [Back]

        #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    [Toc]    [Back]

       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_call-
       back_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_call-
       back_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_call-
           back_arg().

NOTES    [Toc]    [Back]

       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    [Toc]    [Back]

       ssl(3), SSL_new(3)

HISTORY    [Toc]    [Back]

       SSL_CTX_set_msg_callback(), SSL_CTX_set_msg_call-
       back_arg(), SSL_set_msg_callback() and SSL_get_msg_call-
       back_arg() were added in OpenSSL 0.9.7.


OpenBSD 3.6                 2002-09-14                          2