added notes about building with DTLS support

Author: mcr

DTLS.md

@@ -0,0 +1,43 @@
+
+In order to get DTLS to work, you need a patched copy of Openssl.
+Get it here:
+   https://github.com/mcr/openssl/tree/dtls-listen-refactor
+
+build and install it.  You might want to compile without DSO support, as that will
+make it easier for the ruby-openssl module to link in the right code. To do
+that you can do:
+     ./Configure no-shared --prefix=/sandel/3rd/openssl --debug linux-x86_64
+
+(--debug being optional)
+
+The resulting openssl.so will be significantly bigger, btw:
+    %size tmp/x86_64-linux/openssl/2.4.1/openssl.so
+       text    data     bss     dec     hex filename
+    3889567  261788   16856 4168211  3f9a13 tmp/x86_64-linux/openssl/2.4.1/openssl.so
+
+
+Pick a --prefix which is not on your regular paths.  Probably gem can be
+persuaded to do all of this, but hopefully the code will upstreamed sooner
+and the problem will go away.
+
+If DTLSv1_accept() is not available, then the DTLS support will not include
+server side code, only client side code.  No patches are necessary to make
+client-side DTLS work.  To be sure that the patch has been found is enabled
+check for:
+
+    checking for DTLSv1_accept()... yes
+
+
+Then build with:
+
+    rake compile -- --with-openssl-dir=/sandel/3rd/openssl
+
+I don't know how to add the extra arguments required to your Gemfile so that
+it will be built properly during bundle processing. I'm sure that there is a way,
+patches welcome. I do:
+    gem build openssl
+    gem install ./openssl-2.2.0.pre.mcr1.gem
+
+BTW: the pull request is at:
+    https://github.com/openssl/openssl/pull/5024
+and comments would be welcome.