SSL_COMP_ADD_COMPRESS... BSD Library Functions Manual SSL_COMP_ADD_COMPRESS...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 com‐
patible 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 con‐
nection 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:
0 The operation succeeded.
1 The operation failed. Check the error queue to find out the rea‐
son.
SEE ALSOssl(3)BSD April 20, 2024 BSD
