SSL_SESSION_get_compress_id - get details about the compression associated with a session

       Copyright 2017 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>.

3.5.0                                              2025-06-04                  SSL_SESSION_GET_COMPRESS_ID(3SSL)

       If compression has been negotiated for an ssl session then SSL_SESSION_get_compress_id() will return the
       id for the compression method or 0 otherwise. The only built-in supported compression method is zlib
       which has an id of 1.

       SSL_SESSION_get_compress_id - get details about the compression associated with a session

SSL_SESSION_get_compress_id() returns the id of the compression method or 0 if none.

ssl(7)

        #include <openssl/ssl.h>

        unsigned int SSL_SESSION_get_compress_id(const SSL_SESSION *s);