From 336736ef35471888c266336ac2fb17e740979955 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Lutz=20J=C3=A4nicke?= <jaenicke@openssl.org>
Date: Tue, 21 Aug 2001 13:02:58 +0000
Subject: [PATCH] Documentation on how to handle compression methods. Hopefully
 it is clear enough, that it is currently not recommended.

---
 doc/ssl/SSL_COMP_add_compression_method.pod | 64 +++++++++++++++++++++
 doc/ssl/ssl.pod                             |  1 +
 2 files changed, 65 insertions(+)
 create mode 100644 doc/ssl/SSL_COMP_add_compression_method.pod

diff --git a/doc/ssl/SSL_COMP_add_compression_method.pod b/doc/ssl/SSL_COMP_add_compression_method.pod
new file mode 100644
index 0000000000..9e970044a6
--- /dev/null
+++ b/doc/ssl/SSL_COMP_add_compression_method.pod
@@ -0,0 +1,64 @@
+=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
diff --git a/doc/ssl/ssl.pod b/doc/ssl/ssl.pod
index bee252aa8b..cb4260ee80 100644
--- a/doc/ssl/ssl.pod
+++ b/doc/ssl/ssl.pod
@@ -650,6 +650,7 @@ L<openssl(1)|openssl(1)>, L<crypto(3)|crypto(3)>,
 L<SSL_accept(3)|SSL_accept(3)>, L<SSL_clear(3)|SSL_clear(3)>,
 L<SSL_connect(3)|SSL_connect(3)>,
 L<SSL_CIPHER_get_name(3)|SSL_CIPHER_get_name(3)>,
+L<SSL_COMP_add_compression_method(3)|SSL_COMP_add_compression_method(3)>,
 L<SSL_CTX_add_extra_chain_cert(3)|SSL_CTX_add_extra_chain_cert(3)>,
 L<SSL_CTX_add_session(3)|SSL_CTX_add_session(3)>,
 L<SSL_CTX_flush_sessions(3)|SSL_CTX_flush_sessions(3)>,
-- 
2.25.1