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     SSL_CTX_set_msg_callback(3)ug/2002 (0.9.7e)TX_set_msg_callback(3)


     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.


     Page 2                                         (printed 10/20/05)