143 lines
4.7 KiB
Plaintext
143 lines
4.7 KiB
Plaintext
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=pod
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=head1 NAME
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SSL_CTX_set_msg_callback,
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SSL_CTX_set_msg_callback_arg,
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SSL_set_msg_callback,
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SSL_set_msg_callback_arg
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- install callback for observing protocol messages
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=head1 SYNOPSIS
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#include <openssl/ssl.h>
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void SSL_CTX_set_msg_callback(SSL_CTX *ctx,
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void (*cb)(int write_p, int version,
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int content_type, const void *buf,
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size_t len, SSL *ssl, void *arg));
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void SSL_CTX_set_msg_callback_arg(SSL_CTX *ctx, void *arg);
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void SSL_set_msg_callback(SSL *ssl,
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void (*cb)(int write_p, int version,
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int content_type, const void *buf,
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size_t len, SSL *ssl, void *arg));
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void SSL_set_msg_callback_arg(SSL *ssl, void *arg);
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=head1 DESCRIPTION
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SSL_CTX_set_msg_callback() or SSL_set_msg_callback() can be used to
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define a message callback function I<cb> for observing all SSL/TLS
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protocol messages (such as handshake messages) that are received or
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sent, as well as other events that occur during processing.
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SSL_CTX_set_msg_callback_arg() and SSL_set_msg_callback_arg()
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can be used to set argument I<arg> to the callback function, which is
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available for arbitrary application use.
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SSL_CTX_set_msg_callback() and SSL_CTX_set_msg_callback_arg() specify
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default settings that will be copied to new B<SSL> objects by
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L<SSL_new(3)>. SSL_set_msg_callback() and
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SSL_set_msg_callback_arg() modify the actual settings of an B<SSL>
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object. Using a B<NULL> pointer for I<cb> disables the message callback.
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When I<cb> is called by the SSL/TLS library the function arguments have the
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following meaning:
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=over 4
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=item I<write_p>
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This flag is B<0> when a protocol message has been received and B<1>
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when a protocol message has been sent.
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=item I<version>
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The protocol version according to which the protocol message is
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interpreted by the library such as B<TLS1_3_VERSION>, B<TLS1_2_VERSION> etc.
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This is set to 0 for the SSL3_RT_HEADER pseudo content type (see NOTES below).
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=item I<content_type>
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This is one of the content type values defined in the protocol specification
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(B<SSL3_RT_CHANGE_CIPHER_SPEC>, B<SSL3_RT_ALERT>, B<SSL3_RT_HANDSHAKE>; but never
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B<SSL3_RT_APPLICATION_DATA> because the callback will only be called for protocol
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messages). Alternatively it may be a "pseudo" content type. These pseudo
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content types are used to signal some other event in the processing of data (see
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NOTES below).
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=item I<buf>, I<len>
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I<buf> points to a buffer containing the protocol message or other data (in the
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case of pseudo content types), which consists of I<len> bytes. The buffer is no
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longer valid after the callback function has returned.
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=item I<ssl>
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The B<SSL> object that received or sent the message.
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=item I<arg>
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The user-defined argument optionally defined by
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SSL_CTX_set_msg_callback_arg() or SSL_set_msg_callback_arg().
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=back
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=head1 NOTES
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Protocol messages are passed to the callback function after decryption
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and fragment collection where applicable. (Thus record boundaries are
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not visible.)
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If processing a received protocol message results in an error,
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the callback function may not be called. For example, the callback
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function will never see messages that are considered too large to be
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processed.
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Due to automatic protocol version negotiation, I<version> is not
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necessarily the protocol version used by the sender of the message: If
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a TLS 1.0 ClientHello message is received by an SSL 3.0-only server,
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I<version> will be B<SSL3_VERSION>.
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Pseudo content type values may be sent at various points during the processing
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of data. The following pseudo content types are currently defined:
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=over 4
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=item B<SSL3_RT_HEADER>
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Used when a record is sent or received. The B<buf> contains the record header
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bytes only.
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=item B<SSL3_RT_INNER_CONTENT_TYPE>
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Used when an encrypted TLSv1.3 record is sent or received. In encrypted TLSv1.3
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records the content type in the record header is always
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SSL3_RT_APPLICATION_DATA. The real content type for the record is contained in
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an "inner" content type. B<buf> contains the encoded "inner" content type byte.
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=back
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=head1 RETURN VALUES
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SSL_CTX_set_msg_callback(), SSL_CTX_set_msg_callback_arg(), SSL_set_msg_callback()
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and SSL_set_msg_callback_arg() do not return values.
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=head1 SEE ALSO
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L<ssl(7)>, L<SSL_new(3)>
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=head1 HISTORY
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The pseudo content type B<SSL3_RT_INNER_CONTENT_TYPE> was added in OpenSSL 1.1.1.
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=head1 COPYRIGHT
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Copyright 2001-2018 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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