1SSL_COMP_ADD_COMPRESSION_METHOD(3)  OpenSSL SSL_COMP_ADD_COMPRESSION_METHOD(3)
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NAME

6       SSL_COMP_add_compression_method, SSL_COMP_get_compression_methods,
7       SSL_COMP_get0_name, SSL_COMP_get_id, SSL_COMP_free_compression_methods
8       - handle SSL/TLS integrated compression methods
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SYNOPSIS

11        #include <openssl/ssl.h>
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13        int SSL_COMP_add_compression_method(int id, COMP_METHOD *cm);
14        STACK_OF(SSL_COMP) *SSL_COMP_get_compression_methods(void);
15        const char *SSL_COMP_get0_name(const SSL_COMP *comp);
16        int SSL_COMP_get_id(const SSL_COMP *comp);
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18       Deprecated:
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20        #if OPENSSL_API_COMPAT < 0x10100000L
21        void SSL_COMP_free_compression_methods(void)
22        #endif
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DESCRIPTION

25       SSL_COMP_add_compression_method() adds the compression method cm with
26       the identifier id to the list of available compression methods. This
27       list is globally maintained for all SSL operations within this
28       application.  It cannot be set for specific SSL_CTX or SSL objects.
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30       SSL_COMP_get_compression_methods() returns a stack of all of the
31       available compression methods or NULL on error.
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33       SSL_COMP_get0_name() returns the name of the compression method comp.
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35       SSL_COMP_get_id() returns the id of the compression method comp.
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37       SSL_COMP_free_compression_methods() releases any resources acquired to
38       maintain the internal table of compression methods.
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NOTES

41       The TLS standard (or SSLv3) allows the integration of compression
42       methods into the communication. The TLS RFC does however not specify
43       compression methods or their corresponding identifiers, so there is
44       currently no compatible way to integrate compression with unknown
45       peers. It is therefore currently not recommended to integrate
46       compression into applications. Applications for non-public use may
47       agree on certain compression methods. Using different compression
48       methods with the same identifier will lead to connection failure.
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50       An OpenSSL client speaking a protocol that allows compression (SSLv3,
51       TLSv1) will unconditionally send the list of all compression methods
52       enabled with SSL_COMP_add_compression_method() to the server during the
53       handshake.  Unlike the mechanisms to set a cipher list, there is no
54       method available to restrict the list of compression method on a per
55       connection basis.
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57       An OpenSSL server will match the identifiers listed by a client against
58       its own compression methods and will unconditionally activate
59       compression when a matching identifier is found. There is no way to
60       restrict the list of compression methods supported on a per connection
61       basis.
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63       If enabled during compilation, the OpenSSL library will have the
64       COMP_zlib() compression method available.
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RETURN VALUES

67       SSL_COMP_add_compression_method() may return the following values:
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69       0   The operation succeeded.
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71       1   The operation failed. Check the error queue to find out the reason.
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73       SSL_COMP_get_compression_methods() returns the stack of compressions
74       methods or NULL on error.
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76       SSL_COMP_get0_name() returns the name of the compression method or NULL
77       on error.
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79       SSL_COMP_get_id() returns the name of the compression method or -1 on
80       error.
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SEE ALSO

83       ssl(7)
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HISTORY

86       The SSL_COMP_free_compression_methods() function was deprecated in
87       OpenSSL 1.1.0.  The SSL_COMP_get0_name() and SSL_comp_get_id()
88       functions were added in OpenSSL 1.1.0d.
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91       Copyright 2001-2016 The OpenSSL Project Authors. All Rights Reserved.
92
93       Licensed under the OpenSSL license (the "License").  You may not use
94       this file except in compliance with the License.  You can obtain a copy
95       in the file LICENSE in the source distribution or at
96       <https://www.openssl.org/source/license.html>.
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1001.1.1i                            2021-01-26SSL_COMP_ADD_COMPRESSION_METHOD(3)
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