1SSL_CTX_SET_MSG_CALLBACK(3) OpenSSL SSL_CTX_SET_MSG_CALLBACK(3)
2
6 SSL_CTX_set_msg_callback, SSL_CTX_set_msg_callback_arg,
7 SSL_set_msg_callback, SSL_set_msg_callback_arg - install callback for
8 observing protocol messages
9
11 #include <openssl/ssl.h>
12 void SSL_CTX_set_msg_callback(SSL_CTX *ctx,
14 void (*cb)(int write_p, int version,
15 int content_type, const void *buf,
16 size_t len, SSL *ssl, void *arg));
17 void SSL_CTX_set_msg_callback_arg(SSL_CTX *ctx, void *arg);
18 void SSL_set_msg_callback(SSL *ssl,
20 void (*cb)(int write_p, int version,
21 int content_type, const void *buf,
22 size_t len, SSL *ssl, void *arg));
23 void SSL_set_msg_callback_arg(SSL *ssl, void *arg);
24
26 SSL_CTX_set_msg_callback() or SSL_set_msg_callback() can be used to
27 define a message callback function cb for observing all SSL/TLS
28 protocol messages (such as handshake messages) that are received or
29 sent, as well as other events that occur during processing.
30 SSL_CTX_set_msg_callback_arg() and SSL_set_msg_callback_arg() can be
31 used to set argument arg to the callback function, which is available
32 for arbitrary application use.
33 SSL_CTX_set_msg_callback() and SSL_CTX_set_msg_callback_arg() specify
35 default settings that will be copied to new SSL objects by SSL_new(3).
36 SSL_set_msg_callback() and SSL_set_msg_callback_arg() modify the actual
37 settings of an SSL object. Using a NULL pointer for cb disables the
38 message callback.
39 When cb is called by the SSL/TLS library the function arguments have
41 the following meaning:
42 write_p
44 This flag is 0 when a protocol message has been received and 1 when
45 a protocol message has been sent.
46 version
48 The protocol version according to which the protocol message is
49 interpreted by the library such as TLS1_3_VERSION, TLS1_2_VERSION
50 etc. This is set to 0 for the SSL3_RT_HEADER pseudo content type
51 (see NOTES below).
52 content_type
54 This is one of the content type values defined in the protocol
55 specification (SSL3_RT_CHANGE_CIPHER_SPEC, SSL3_RT_ALERT,
56 SSL3_RT_HANDSHAKE; but never SSL3_RT_APPLICATION_DATA because the
57 callback will only be called for protocol messages). Alternatively
58 it may be a "pseudo" content type. These pseudo content types are
59 used to signal some other event in the processing of data (see
60 NOTES below).
61 buf, len
63 buf points to a buffer containing the protocol message or other
64 data (in the case of pseudo content types), which consists of len
65 bytes. The buffer is no longer valid after the callback function
66 has returned.
67 ssl The SSL object that received or sent the message.
69 arg The user-defined argument optionally defined by
71 SSL_CTX_set_msg_callback_arg() or SSL_set_msg_callback_arg().
72
74 Protocol messages are passed to the callback function after decryption
75 and fragment collection where applicable. (Thus record boundaries are
76 not visible.)
77 If processing a received protocol message results in an error, the
79 callback function may not be called. For example, the callback
80 function will never see messages that are considered too large to be
81 processed.
82 Due to automatic protocol version negotiation, version is not
84 necessarily the protocol version used by the sender of the message: If
85 a TLS 1.0 ClientHello message is received by an SSL 3.0-only server,
86 version will be SSL3_VERSION.
87 Pseudo content type values may be sent at various points during the
89 processing of data. The following pseudo content types are currently
90 defined:
91 SSL3_RT_HEADER
93 Used when a record is sent or received. The buf contains the record
94 header bytes only.
95 SSL3_RT_INNER_CONTENT_TYPE
97 Used when an encrypted TLSv1.3 record is sent or received. In
98 encrypted TLSv1.3 records the content type in the record header is
99 always SSL3_RT_APPLICATION_DATA. The real content type for the
100 record is contained in an "inner" content type. buf contains the
101 encoded "inner" content type byte.
102
104 SSL_CTX_set_msg_callback(), SSL_CTX_set_msg_callback_arg(),
105 SSL_set_msg_callback() and SSL_set_msg_callback_arg() do not return
106 values.
107
109 ssl(7), SSL_new(3)
110
112 The pseudo content type SSL3_RT_INNER_CONTENT_TYPE was added in OpenSSL
113 1.1.1.
114
116 Copyright 2001-2018 The OpenSSL Project Authors. All Rights Reserved.
117 Licensed under the OpenSSL license (the "License"). You may not use
119 this file except in compliance with the License. You can obtain a copy
120 in the file LICENSE in the source distribution or at
121 <https://www.openssl.org/source/license.html>.
1221.1.1q 2022-07-21 SSL_CTX_SET_MSG_CALLBACK(3)