/usr/man/cat.3/SSL_COMP_add_compression_method.3.Z

NAME

       SSL_COMP_add_compression_method, SSL_COMP_free_compression_methods -
       handle SSL/TLS integrated compression methods

SYNOPSIS

        #include <openssl/ssl.h>

        int SSL_COMP_add_compression_method(int id, COMP_METHOD *cm);

        +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 applica-
       tion.  It cannot be set for specific SSL_CTX or SSL objects.

       SSL_COMP_free_compression_methods() frees the internal table of com-
       pression methods that were built internally, and possibly augmented by
       adding SSL_COMP_add_compression_method().

NOTES

       The TLS standard (or SSLv3) allows the integration of compression meth-
       ods into the communication. The TLS RFC does however not specify com-
       pression methods or their corresponding identifiers, so there is cur-
       rently 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 com-
       pression 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 compres-
       sion 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.

WARNINGS

       Once the identities of the compression methods for the TLS protocol
       have been standardized, the compression API will most likely be
       changed. Using it in the current state is not recommended.

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.

SEE ALSO

       ssl(3)

1.0.2t                            2019-09-10SSL_COMP_add_compression_method(3)
See also SSL_COMP_free_compression_methods(3)