doc/man3/SSL_CTX_set_msg_callback.pod

   1 =pod
   2
   3 =head1 NAME
   4
   5 SSL_CTX_set_msg_callback,
   6 SSL_CTX_set_msg_callback_arg,
   7 SSL_set_msg_callback,
   8 SSL_set_msg_callback_arg,
   9 SSL_trace
  10 - install callback for observing protocol messages
  11
  12 =head1 SYNOPSIS
  13
  14  #include <openssl/ssl.h>
  15
  16  void SSL_CTX_set_msg_callback(SSL_CTX *ctx,
  17                                void (*cb)(int write_p, int version,
  18                                           int content_type, const void *buf,
  19                                           size_t len, SSL *ssl, void *arg));
  20  void SSL_CTX_set_msg_callback_arg(SSL_CTX *ctx, void *arg);
  21
  22  void SSL_set_msg_callback(SSL *ssl,
  23                            void (*cb)(int write_p, int version,
  24                                       int content_type, const void *buf,
  25                                       size_t len, SSL *ssl, void *arg));
  26  void SSL_set_msg_callback_arg(SSL *ssl, void *arg);
  27
  28  void SSL_trace(int write_p, int version, int content_type,
  29                 const void *buf, size_t len, SSL *ssl, void *arg);
  30
  31 =head1 DESCRIPTION
  32
  33 SSL_CTX_set_msg_callback() or SSL_set_msg_callback() can be used to
  34 define a message callback function I<cb> for observing all SSL/TLS/QUIC
  35 protocol messages (such as handshake messages) that are received or
  36 sent, as well as other events that occur during processing.
  37 SSL_CTX_set_msg_callback_arg() and SSL_set_msg_callback_arg()
  38 can be used to set argument I<arg> to the callback function, which is
  39 available for arbitrary application use.
  40
  41 SSL_CTX_set_msg_callback() and SSL_CTX_set_msg_callback_arg() specify
  42 default settings that will be copied to new B<SSL> objects by
  43 L<SSL_new(3)>. SSL_set_msg_callback() and
  44 SSL_set_msg_callback_arg() modify the actual settings of an B<SSL>
  45 object. Using a B<NULL> pointer for I<cb> disables the message callback.
  46
  47 When I<cb> is called by the SSL/TLS/QUIC library the function arguments have the
  48 following meaning:
  49
  50 =over 4
  51
  52 =item I<write_p>
  53
  54 This flag is B<0> when a protocol message has been received and B<1>
  55 when a protocol message has been sent.
  56
  57 =item I<version>
  58
  59 The protocol version according to which the protocol message is
  60 interpreted by the library such as B<TLS1_3_VERSION>, B<TLS1_2_VERSION>,
  61 B<OSSL_QUIC1_VERSION> etc. This is set to 0 for the SSL3_RT_HEADER pseudo
  62 content type (see NOTES below).
  63
  64 =item I<content_type>
  65
  66 This is one of the content type values defined in the protocol specification
  67 (B<SSL3_RT_CHANGE_CIPHER_SPEC>, B<SSL3_RT_ALERT>, B<SSL3_RT_HANDSHAKE>; but never
  68 B<SSL3_RT_APPLICATION_DATA> because the callback will only be called for protocol
  69 messages). Alternatively it may be a "pseudo" content type. These pseudo
  70 content types are used to signal some other event in the processing of data (see
  71 NOTES below).
  72
  73 =item I<buf>, I<len>
  74
  75 I<buf> points to a buffer containing the protocol message or other data (in the
  76 case of pseudo content types), which consists of I<len> bytes. The buffer is no
  77 longer valid after the callback function has returned.
  78
  79 =item I<ssl>
  80
  81 The B<SSL> object that received or sent the message.
  82
  83 =item I<arg>
  84
  85 The user-defined argument optionally defined by
  86 SSL_CTX_set_msg_callback_arg() or SSL_set_msg_callback_arg().
  87
  88 =back
  89
  90 The SSL_trace() function can be used as a pre-written callback in a call to
  91 SSL_CTX_set_msg_callback() or SSL_set_msg_callback(). It requires a BIO to be
  92 set as the callback argument via SSL_CTX_set_msg_callback_arg() or
  93 SSL_set_msg_callback_arg(). Setting this callback will cause human readable
  94 diagostic tracing information about an SSL/TLS/QUIC connection to be written to
  95 the BIO.
  96
  97 =head1 NOTES
  98
  99 Protocol messages are passed to the callback function after decryption
 100 and fragment collection where applicable. (Thus record boundaries are
 101 not visible.)
 102
 103 If processing a received protocol message results in an error,
 104 the callback function may not be called.  For example, the callback
 105 function will never see messages that are considered too large to be
 106 processed.
 107
 108 Due to automatic protocol version negotiation, I<version> is not
 109 necessarily the protocol version used by the sender of the message: If
 110 a TLS 1.0 ClientHello message is received by an SSL 3.0-only server,
 111 I<version> will be B<SSL3_VERSION>.
 112
 113 Pseudo content type values may be sent at various points during the processing
 114 of data. The following pseudo content types are currently defined:
 115
 116 =over 4
 117
 118 =item B<SSL3_RT_HEADER>
 119
 120 Used when a TLS record is sent or received. The B<buf> contains the record header
 121 bytes only.
 122
 123 =item B<SSL3_RT_INNER_CONTENT_TYPE>
 124
 125 Used when an encrypted TLSv1.3 record is sent or received. In encrypted TLSv1.3
 126 records the content type in the record header is always
 127 SSL3_RT_APPLICATION_DATA. The real content type for the record is contained in
 128 an "inner" content type. B<buf> contains the encoded "inner" content type byte.
 129
 130 =item B<SSL3_RT_QUIC_DATAGRAM>
 131
 132 Used when a QUIC datagram is sent or received.
 133
 134 =item B<SSL3_RT_QUIC_PACKET>
 135
 136 Used when a QUIC packet is sent or received.
 137
 138 =item B<SSL3_RT_QUIC_FRAME_FULL>
 139
 140 Used when a QUIC frame is sent or received. This is only used for non-crypto
 141 and stream data related frames. The full QUIC frame data is supplied.
 142
 143 =item B<SSL3_RT_QUIC_FRAME_HEADER>
 144
 145 Used when a QUIC stream data or crypto frame is sent or received. Only the QUIC
 146 frame header data is supplied.
 147
 148 =item B<SSL3_RT_QUIC_FRAME_PADDING>
 149
 150 Used when a sequence of one or more QUIC padding frames is sent or received.
 151 A padding frame consists of a single byte and it is common to have multiple
 152 such frames in a sequence. Rather than supplying each frame individually the
 153 callback will supply all the padding frames in one go via this pseudo content
 154 type.
 155
 156 =back
 157
 158 =head1 RETURN VALUES
 159
 160 SSL_CTX_set_msg_callback(), SSL_CTX_set_msg_callback_arg(), SSL_set_msg_callback()
 161 and SSL_set_msg_callback_arg() do not return values.
 162
 163 =head1 SEE ALSO
 164
 165 L<ssl(7)>, L<SSL_new(3)>
 166
 167 =head1 HISTORY
 168
 169 The pseudo content type B<SSL3_RT_INNER_CONTENT_TYPE> was added in OpenSSL 1.1.1.
 170
 171 The pseudo content types B<SSL3_RT_QUIC_DATAGRAM>, B<SSL3_RT_QUIC_PACKET>,
 172 B<SSL3_RT_QUIC_FRAME_FULL>, B<SSL3_RT_QUIC_FRAME_HEADER> and
 173 B<SSL3_RT_QUIC_FRAME_PADDING> were added in OpenSSL 3.2.
 174
 175 =head1 COPYRIGHT
 176
 177 Copyright 2001-2023 The OpenSSL Project Authors. All Rights Reserved.
 178
 179 Licensed under the Apache License 2.0 (the "License").  You may not use
 180 this file except in compliance with the License.  You can obtain a copy
 181 in the file LICENSE in the source distribution or at
 182 L<https://www.openssl.org/source/license.html>.
 183
 184 =cut