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 The buffer is no longer valid after the callback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.
