SSL_COMP_add_compression_method - handle SSL/TLS integrated compression methods
int SSL_COMP_add_compression_method(int id, COMP_METHOD *cm);
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
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
and (when especially enabled during
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.
may return the following values:
- The operation succeeded.
- The operation failed. Check the error queue to find out the