SSL_COMP_add_compression_method(3)SSL_COMP_add_compression_method(3)NAMESSL_COMP_add_compression_method - Handle SSL/TLS integrated compression
methods
SYNOPSIS
#include <openssl/ssl.h>
int SSL_COMP_add_compression_method(
int id,
COMP_METHOD *cm );
DESCRIPTION
The SSL_COMP_add_compression_method() function 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.
NOTES
The TLS standard (or SSLv3) allows the integration of compression meth‐
ods into the communication. However, the TLS RFC does not specify com‐
pression methods or their corresponding identifiers, so there is no
compatible way to integrate compression with unknown peers. We do not
recommend integrating compression into applications. Applications for
non-public use may agree on certain compression methods. Using differ‐
ent compression methods with the same identifier will lead to connec‐
tion 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.
The OpenSSL library has the compression methods COMP_rle() and (when
especially enabled during compilation) COMP_zlib() available.
Once the identities of the compression methods for the TLS protocol
have been standardized, the compression API will most likely be
changed. We do not recommend using it in its current state.
RETURN VALUES
The following return values can occur: The operation failed. Check the
error queue to learn the reason. The operation succeeded.
SEE ALSO
Functions: ssl(3)SSL_COMP_add_compression_method(3)
