SSL_COMP_add_compression_methOpSSL_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);
DESCRIPTIONSSL_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.
NOTES
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
basis.
The OpenSSL library has the compression methods COMP_rle()
and (when especially enabled during compilation)
COMP_zlib() 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 VALUESSSL_COMP_add_compression_method() may return the following
values:
1 The operation succeeded.
0 The operation failed. Check the error queue to find
out the reason.
SEE ALSOssl(3)23/Aug/2001 0SSL_COMP_add_compression_method(3)
