1=pod 2 3=head1 NAME 4 5SSL_CTX_set_msg_callback, 6SSL_CTX_set_msg_callback_arg, 7SSL_set_msg_callback, 8SSL_set_msg_callback_arg, 9SSL_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 33SSL_CTX_set_msg_callback() or SSL_set_msg_callback() can be used to 34define a message callback function I<cb> for observing all SSL/TLS/QUIC 35protocol messages (such as handshake messages) that are received or 36sent, as well as other events that occur during processing. 37SSL_CTX_set_msg_callback_arg() and SSL_set_msg_callback_arg() 38can be used to set argument I<arg> to the callback function, which is 39available for arbitrary application use. 40 41SSL_CTX_set_msg_callback() and SSL_CTX_set_msg_callback_arg() specify 42default settings that will be copied to new B<SSL> objects by 43L<SSL_new(3)>. SSL_set_msg_callback() and 44SSL_set_msg_callback_arg() modify the actual settings of an B<SSL> 45object. Using a B<NULL> pointer for I<cb> disables the message callback. 46 47When I<cb> is called by the SSL/TLS/QUIC library the function arguments have the 48following meaning: 49 50=over 4 51 52=item I<write_p> 53 54This flag is B<0> when a protocol message has been received and B<1> 55when a protocol message has been sent. 56 57=item I<version> 58 59The protocol version according to which the protocol message is 60interpreted by the library such as B<TLS1_3_VERSION>, B<TLS1_2_VERSION>, 61B<OSSL_QUIC1_VERSION> etc. For the SSL3_RT_HEADER pseudo 62content type (see NOTES below) this value will be the decoded 63version/legacy_version field of the record header. 64 65=item I<content_type> 66 67This is one of the content type values defined in the protocol specification 68(B<SSL3_RT_CHANGE_CIPHER_SPEC>, B<SSL3_RT_ALERT>, B<SSL3_RT_HANDSHAKE>; but never 69B<SSL3_RT_APPLICATION_DATA> because the callback will only be called for protocol 70messages). Alternatively it may be a "pseudo" content type. These pseudo 71content types are used to signal some other event in the processing of data (see 72NOTES below). 73 74=item I<buf>, I<len> 75 76I<buf> points to a buffer containing the protocol message or other data (in the 77case of pseudo content types), which consists of I<len> bytes. The buffer is no 78longer valid after the callback function has returned. 79 80=item I<ssl> 81 82The B<SSL> object that received or sent the message. 83 84=item I<arg> 85 86The user-defined argument optionally defined by 87SSL_CTX_set_msg_callback_arg() or SSL_set_msg_callback_arg(). 88 89=back 90 91The SSL_trace() function can be used as a pre-written callback in a call to 92SSL_CTX_set_msg_callback() or SSL_set_msg_callback(). It requires a BIO to be 93set as the callback argument via SSL_CTX_set_msg_callback_arg() or 94SSL_set_msg_callback_arg(). Setting this callback will cause human readable 95diagostic tracing information about an SSL/TLS/QUIC connection to be written to 96the BIO. 97 98=head1 NOTES 99 100Protocol messages are passed to the callback function after decryption 101and fragment collection where applicable. (Thus record boundaries are 102not visible.) 103 104If processing a received protocol message results in an error, 105the callback function may not be called. For example, the callback 106function will never see messages that are considered too large to be 107processed. 108 109Due to automatic protocol version negotiation, I<version> is not 110necessarily the protocol version used by the sender of the message: If 111a TLS 1.0 ClientHello message is received by an SSL 3.0-only server, 112I<version> will be B<SSL3_VERSION>. 113 114Pseudo content type values may be sent at various points during the processing 115of data. The following pseudo content types are currently defined: 116 117=over 4 118 119=item B<SSL3_RT_HEADER> 120 121Used when a TLS record is sent or received. The B<buf> contains the record header 122bytes only. 123 124=item B<SSL3_RT_INNER_CONTENT_TYPE> 125 126Used when an encrypted TLSv1.3 record is sent or received. In encrypted TLSv1.3 127records the content type in the record header is always 128SSL3_RT_APPLICATION_DATA. The real content type for the record is contained in 129an "inner" content type. B<buf> contains the encoded "inner" content type byte. 130 131=item B<SSL3_RT_QUIC_DATAGRAM> 132 133Used when a QUIC datagram is sent or received. 134 135=item B<SSL3_RT_QUIC_PACKET> 136 137Used when a QUIC packet is sent or received. 138 139=item B<SSL3_RT_QUIC_FRAME_FULL> 140 141Used when a QUIC frame is sent or received. This is only used for non-crypto 142and stream data related frames. The full QUIC frame data is supplied. 143 144=item B<SSL3_RT_QUIC_FRAME_HEADER> 145 146Used when a QUIC stream data or crypto frame is sent or received. Only the QUIC 147frame header data is supplied. 148 149=item B<SSL3_RT_QUIC_FRAME_PADDING> 150 151Used when a sequence of one or more QUIC padding frames is sent or received. 152A padding frame consists of a single byte and it is common to have multiple 153such frames in a sequence. Rather than supplying each frame individually the 154callback will supply all the padding frames in one go via this pseudo content 155type. 156 157=back 158 159=head1 RETURN VALUES 160 161SSL_CTX_set_msg_callback(), SSL_CTX_set_msg_callback_arg(), SSL_set_msg_callback() 162and SSL_set_msg_callback_arg() do not return values. 163 164=head1 SEE ALSO 165 166L<ssl(7)>, L<SSL_new(3)> 167 168=head1 HISTORY 169 170The pseudo content type B<SSL3_RT_INNER_CONTENT_TYPE> was added in OpenSSL 1.1.1. 171 172The pseudo content types B<SSL3_RT_QUIC_DATAGRAM>, B<SSL3_RT_QUIC_PACKET>, 173B<SSL3_RT_QUIC_FRAME_FULL>, B<SSL3_RT_QUIC_FRAME_HEADER> and 174B<SSL3_RT_QUIC_FRAME_PADDING> were added in OpenSSL 3.2. 175 176In versions previous to OpenSSL 3.0 I<cb> was called with 0 as I<version> for 177the pseudo content type B<SSL3_RT_HEADER> for TLS records. 178 179In versions previous to OpenSSL 3.2 I<cb> was called with 0 as I<version> for 180the pseudo content type B<SSL3_RT_HEADER> for DTLS records. 181 182=head1 COPYRIGHT 183 184Copyright 2001-2023 The OpenSSL Project Authors. All Rights Reserved. 185 186Licensed under the Apache License 2.0 (the "License"). You may not use 187this file except in compliance with the License. You can obtain a copy 188in the file LICENSE in the source distribution or at 189L<https://www.openssl.org/source/license.html>. 190 191=cut 192