FEAT: Added Server Name Indication extension into TLS scheme

More details: https://tools.ietf.org/html/rfc6066#section-3

   TLS does not provide a mechanism for a client to tell a server the
   name of the server it is contacting.  It may be desirable for clients
   to provide this information to facilitate secure connections to
   servers that host multiple 'virtual' servers at a single underlying
   network address.

   In order to provide any of the server names, clients MAY include an
   extension of type "server_name" in the (extended) client hello.

Author: Oldes

src/mezz/prot-tls.r

@@ -408,11 +408,31 @@ client-hello: function [
 ] [
 	change-state ctx 'CLIENT_HELLO
 	with ctx [
-		;initialize checksum port(s)
+
+		extensions: make binary! 16
+
+		;- Server Name Indication (extension)
+		;  https://tools.ietf.org/html/rfc6066#section-3
+		if all [
+			ctx/connection
+			host-name: ctx/connection/spec/host
+		][
+			host-name: to binary! host-name
+			length-name: length? host-name
+
+			binary/write extensions compose [
+				UI16  0                ; extension type (server_name=0)
+				UI16 (5 + length-name) 
+				UI16 (3 + length-name)
+				UI8   0
+				UI16  :length-name
+				BYTES :host-name
+			]
+		]
 
 		;precomputing the extension's lengths so I can write them in one WRITE call
 		length-signatures:  2 + length? supported-signature-algorithms
-		length-extensions:  4 + length-signatures
+		length-extensions:  4 + length-signatures + length? extensions
 		length-message:    41 + length-extensions + length? suported-cipher-suites
 		length-record:      4 + length-message
 
@@ -434,6 +454,7 @@ client-hello: function [
 			UI16      13                  ; extension type: signature-algorithms
 			UI16      :length-signatures  ; note: there is another length following
 			UI16BYTES :supported-signature-algorithms
+			BYTES     :extensions
 		]
 
 		out/buffer: head out/buffer
@@ -1376,7 +1397,7 @@ TLS-read-handshake-message: function [
 									signature: decode 'der signature
 								]
 								;note tls1.3 is different a little bit here!
-								message-hash <> signature/sequence/octet_string
+								(probe message-hash) <> probe signature/sequence/octet_string
 							][
 								log-error "Failed to validate signature"
 								if error? err [print err]