Documentation on how to handle compression methods.

Hopefully it is clear enough, that it is currently not recommended.

1 files changed, 64 insertions, 0 deletions

diff --git a/doc/ssl/SSL_COMP_add_compression_method.pod b/doc/ssl/SSL_COMP_add_compression_method.pod
new file mode 100644
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+++ b/doc/ssl/SSL_COMP_add_compression_method.pod
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+=pod
+
+=head1 NAME
+
+SSL_COMP_add_compression_method - handle SSL/TLS integrated compression methods
+
+=head1 SYNOPSIS
+
+ #include <openssl/ssl.h>
+
+ int SSL_COMP_add_compression_method(int id, COMP_METHOD *cm);
+
+=head1 DESCRIPTION
+
+SSL_COMP_add_compression_method() adds the compression method B<cm> with
+the identifier B<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.
+
+=head1 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 B<COMP_rle()> and (when
+especially enabled during compilation) B<COMP_zlib()> available.
+
+=head1 RETURN VALUES
+
+SSL_COMP_add_compression_method() may return the following values:
+
+=over 4
+
+=item 1
+
+The operation succeeded.
+
+=item 0
+
+The operation failed. Check the error queue to find out the reason.
+
+=back
+
+=head1 SEE ALSO
+
+L<ssl(3)|ssl(3)>
+
+=cut