Updated: 2022/Sep/29

Please read Privacy Policy. It's for your privacy.

SSL_COMP_add_compression_method(3)  OpenSSL SSL_COMP_add_compression_method(3)

       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

       libcrypto, -lcrypto

        #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);


        #if OPENSSL_API_COMPAT < 0x10100000L
        void SSL_COMP_free_compression_methods(void)

       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.

       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

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

       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


       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 2001-2016 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (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

1.1.1i                            2019-03-12