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 *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);
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 The buffer is no longer valid after the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.