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SSL_COMP_add_compression_method(3) OpenSSL SSL_COMP_add_compression_method(3)
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SSL_COMP_get0_name, SSL_COMP_get_id, SSL_COMP_free_compression_methods
- handle SSL/TLS integrated compression methods
int SSL_COMP_add_compression_method(int id, COMP_METHOD *cm);
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):
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
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
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 2001-2021 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