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SSL_COMP_add_compression_method(3)  OpenSSL SSL_COMP_add_compression_method(3)



NAME
       SSL_COMP_add_compression_method, SSL_COMP_get_compression_methods,
       SSL_COMP_get0_name, SSL_COMP_get_id, SSL_COMP_free_compression_methods
       - handle SSL/TLS integrated compression methods

LIBRARY
       libcrypto, -lcrypto

SYNOPSIS
        #include <openssl/ssl.h>

        int SSL_COMP_add_compression_method(int id, COMP_METHOD *cm);
        STACK_OF(SSL_COMP) *SSL_COMP_get_compression_methods(void);
        const char *SSL_COMP_get0_name(const SSL_COMP *comp);
        int SSL_COMP_get_id(const SSL_COMP *comp);

       The following function has been deprecated since OpenSSL 1.1.0, and can
       be hidden entirely by defining OPENSSL_API_COMPAT with a suitable
       version value, see openssl_user_macros(7):

        void SSL_COMP_free_compression_methods(void);

DESCRIPTION
       SSL_COMP_add_compression_method() adds the compression method cm with
       the identifier id to the list of available compression methods. This
       list is globally maintained for all SSL operations within this
       application.  It cannot be set for specific SSL_CTX or SSL objects.

       SSL_COMP_get_compression_methods() returns a stack of all of the
       available compression methods or NULL on error.

       SSL_COMP_get0_name() returns the name of the compression method comp.

       SSL_COMP_get_id() returns the id of the compression method comp.

       SSL_COMP_free_compression_methods() releases any resources acquired to
       maintain the internal table of compression methods.

NOTES
       The TLS standard (or SSLv3) allows the integration of compression
       methods into the communication. The TLS RFC does however not specify
       compression methods or their corresponding identifiers, so there is
       currently no compatible way to integrate compression with unknown
       peers. It is therefore currently not recommended to integrate
       compression into applications. Applications for non-public use may
       agree on certain compression methods. Using different compression
       methods with the same identifier will lead to connection failure.

       An OpenSSL client speaking a protocol that allows compression (SSLv3,
       TLSv1) will unconditionally send the list of all compression methods
       enabled with SSL_COMP_add_compression_method() to the server during the
       handshake.  Unlike the mechanisms to set a cipher list, there is no
       method available to restrict the list of compression method on a per
       connection basis.

       An OpenSSL server will match the identifiers listed by a client against
       its own compression methods and will unconditionally activate
       compression when a matching identifier is found. There is no way to
       restrict the list of compression methods supported on a per connection
       basis.

       If enabled during compilation, the OpenSSL library will have the
       COMP_zlib() compression method available.

RETURN VALUES
       SSL_COMP_add_compression_method() may return the following values:

       0   The operation succeeded.

       1   The operation failed. Check the error queue to find out the reason.

       SSL_COMP_get_compression_methods() returns the stack of compressions
       methods or NULL on error.

       SSL_COMP_get0_name() returns the name of the compression method or NULL
       on error.

       SSL_COMP_get_id() returns the name of the compression method or -1 on
       error.

SEE ALSO
       ssl(7)

HISTORY
       The SSL_COMP_free_compression_methods() function was deprecated in
       OpenSSL 1.1.0.  The SSL_COMP_get0_name() and SSL_comp_get_id()
       functions were added in OpenSSL 1.1.0d.

COPYRIGHT
       Copyright 2001-2021 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (the "License").  You may not use
       this file except in compliance with the License.  You can obtain a copy
       in the file LICENSE in the source distribution or at
       <https://www.openssl.org/source/license.html>.



3.0.12                            2023-05-07
                                            SSL_COMP_add_compression_method(3)