1SSL_CTX_set_msg_callback(3)         OpenSSL        SSL_CTX_set_msg_callback(3)
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NAME

6       SSL_CTX_set_msg_callback, SSL_CTX_set_msg_callback_arg,
7       SSL_set_msg_callback, SSL_get_msg_callback_arg - install callback for
8       observing protocol messages
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SYNOPSIS

11        #include <openssl/ssl.h>
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13        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));
14        void SSL_CTX_set_msg_callback_arg(SSL_CTX *ctx, void *arg);
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16        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));
17        void SSL_set_msg_callback_arg(SSL *ssl, void *arg);
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DESCRIPTION

20       SSL_CTX_set_msg_callback() or SSL_set_msg_callback() can be used to
21       define a message callback function cb for observing all SSL/TLS
22       protocol messages (such as handshake messages) that are received or
23       sent.  SSL_CTX_set_msg_callback_arg() and SSL_set_msg_callback_arg()
24       can be used to set argument arg to the callback function, which is
25       available for arbitrary application use.
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27       SSL_CTX_set_msg_callback() and SSL_CTX_set_msg_callback_arg() specify
28       default settings that will be copied to new SSL objects by SSL_new(3).
29       SSL_set_msg_callback() and SSL_set_msg_callback_arg() modify the actual
30       settings of an SSL object. Using a 0 pointer for cb disables the
31       message callback.
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33       When cb is called by the SSL/TLS library for a protocol message, the
34       function arguments have the following meaning:
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36       write_p
37           This flag is 0 when a protocol message has been received and 1 when
38           a protocol message has been sent.
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40       version
41           The protocol version according to which the protocol message is
42           interpreted by the library. Currently, this is one of SSL2_VERSION,
43           SSL3_VERSION and TLS1_VERSION (for SSL 2.0, SSL 3.0 and TLS 1.0,
44           respectively).
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46       content_type
47           In the case of SSL 2.0, this is always 0.  In the case of SSL 3.0
48           or TLS 1.0, this is one of the ContentType values defined in the
49           protocol specification (change_cipher_spec(20), alert(21),
50           handshake(22); but never application_data(23) because the callback
51           will only be called for protocol messages).
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53       buf, len
54           buf points to a buffer containing the protocol message, which
55           consists of len bytes. The buffer is no longer valid after the
56           callback function has returned.
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58       ssl The SSL object that received or sent the message.
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60       arg The user-defined argument optionally defined by
61           SSL_CTX_set_msg_callback_arg() or SSL_set_msg_callback_arg().
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NOTES

64       Protocol messages are passed to the callback function after decryption
65       and fragment collection where applicable. (Thus record boundaries are
66       not visible.)
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68       If processing a received protocol message results in an error, the
69       callback function may not be called.  For example, the callback
70       function will never see messages that are considered too large to be
71       processed.
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73       Due to automatic protocol version negotiation, version is not
74       necessarily the protocol version used by the sender of the message: If
75       a TLS 1.0 ClientHello message is received by an SSL 3.0-only server,
76       version will be SSL3_VERSION.
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SEE ALSO

79       ssl(3), SSL_new(3)
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HISTORY

82       SSL_CTX_set_msg_callback(), SSL_CTX_set_msg_callback_arg(),
83       SSL_set_msg_callback() and SSL_get_msg_callback_arg() were added in
84       OpenSSL 0.9.7.
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881.0.2o                            2020-01-28       SSL_CTX_set_msg_callback(3)
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