remove public header from all messages, fix envelope sizes (#251)

* fix envelope sizes

* only send sender DH pub key for per-queue E2E with confirmation message

src/Simplex/Messaging/Encoding.hs

@@ -1,5 +1,6 @@
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TypeApplications #-}
@@ -66,6 +67,14 @@ instance Encoding ByteString where
   smpEncode s = B.cons (w2c len) s where len = fromIntegral $ B.length s
   smpP = A.take . fromIntegral . c2w =<< A.anyChar
 
+instance Encoding a => Encoding (Maybe a) where
+  smpEncode s = maybe "\0" (("\1" <>) . smpEncode) s
+  smpP =
+    smpP >>= \case
+      '\0' -> pure Nothing
+      '\1' -> Just <$> smpP
+      _ -> fail "invalid Maybe tag"
+
 newtype Tail = Tail {unTail :: ByteString}
 
 instance Encoding Tail where