SSL_COMP_add_compression_method — handle SSL/TLS integrated compression methods
SSL_COMP_add_compression_method(int id, COMP_METHOD *cm);
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.
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
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. Using it in the current state is not recommended.
SSL_COMP_add_compression_method() may return the following
The operation succeeded.
The operation failed. Check the error queue to find out the