1 files changed, 9 insertions, 0 deletions

diff --git a/ToxCrypto.hs b/ToxCrypto.hs
index 98e02e91..cae7e251 100644
--- a/ToxCrypto.hs
+++ b/ToxCrypto.hs
@@ -17,6 +17,8 @@ module ToxCrypto
     , getRemainingEncrypted
     , putEncrypted
     , Auth
+    , Sized(..)
+    , Size(..)
     ) where
 
 import qualified Crypto.Cipher.Salsa    as Salsa
@@ -81,6 +83,13 @@ instance Sized a => Serialize (Encrypted a) where
             ConstSize n -> Encrypted <$> getBytes (16 + n) -- 16 extra for Poly1305 mac
     put = putEncrypted
 
+instance (Sized a, Sized b) => Sized (a,b) where
+    size = case (size :: Size a, size :: Size b) of
+        (ConstSize a , ConstSize b) -> ConstSize $ a + b
+        (VarSize f   , ConstSize b) -> VarSize $ \(a, _) -> f a + b
+        (ConstSize a , VarSize g)   -> VarSize $ \(_, b) -> a + g b
+        (VarSize f   , VarSize g)   -> VarSize $ \(a, b) -> f a + g b
+
 getRemainingEncrypted :: Get (Encrypted a)
 getRemainingEncrypted = Encrypted <$> (remaining >>= getBytes)