3 files changed, 21 insertions, 0 deletions

diff --git a/src/Data/Torrent.hs b/src/Data/Torrent.hs
index 7d3917f2..7833c261 100644
--- a/src/Data/Torrent.hs
+++ b/src/Data/Torrent.hs
@@ -140,6 +140,10 @@ instance Hashable InfoDict where
   hashWithSalt = Hashable.hashUsing idInfoHash
   {-# INLINE hashWithSalt #-}
 
+-- | Empty info dictionary with zero-length content.
+instance Default InfoDict where
+  def = infoDictionary def def False
+
 -- | Smart constructor: add a info hash to info dictionary.
 infoDictionary :: LayoutInfo -> PieceInfo -> Bool -> InfoDict
 infoDictionary li pinfo private = InfoDict ih li pinfo private
@@ -340,6 +344,10 @@ instance Pretty Torrent where
         "Publisher URL" <:>? ((text . show) <$> tPublisherURL) $$
         "Signature"     <:>? ((text . show) <$> tSignature)
 
+-- | No files, no trackers, no nodes, etc...
+instance Default Torrent where
+  def = nullTorrent def
+
 -- | A simple torrent contains only required fields.
 nullTorrent :: InfoDict -> Torrent
 nullTorrent info = Torrent
diff --git a/src/Data/Torrent/Layout.hs b/src/Data/Torrent/Layout.hs
index a4b55b3d..ef8d45eb 100644
--- a/src/Data/Torrent/Layout.hs
+++ b/src/Data/Torrent/Layout.hs
@@ -71,6 +71,7 @@ import Data.BEncode.Types
 import Data.ByteString as BS
 import Data.ByteString.Base16 as Base16
 import Data.ByteString.Char8 as BC
+import Data.Default
 import Data.Foldable as F
 import Data.List as L
 import Data.Text as T
@@ -222,6 +223,10 @@ instance NFData LayoutInfo where
   rnf SingleFile {..} = ()
   rnf MultiFile  {..} = rnf liFiles
 
+-- | Empty multifile layout.
+instance Default LayoutInfo where
+  def = MultiFile [] ""
+
 getLayoutInfo :: Get LayoutInfo
 getLayoutInfo = single <|> multi
   where
diff --git a/src/Data/Torrent/Piece.hs b/src/Data/Torrent/Piece.hs
index 74a2469a..03335819 100644
--- a/src/Data/Torrent/Piece.hs
+++ b/src/Data/Torrent/Piece.hs
@@ -56,6 +56,7 @@ import Data.Bits.Extras
 import           Data.ByteString as BS
 import qualified Data.ByteString.Lazy as BL
 import qualified Data.ByteString.Base64 as Base64
+import Data.Default
 import Data.Int
 import Data.Text.Encoding as T
 import Data.Typeable
@@ -170,6 +171,10 @@ instance FromJSON HashList where
   parseJSON = withText "HashArray" $
     either fail (return . HashList) . Base64.decode . T.encodeUtf8
 
+-- | Empty hash list.
+instance Default HashList where
+  def = HashList ""
+
 -- | Part of torrent file used for torrent content validation.
 data PieceInfo = PieceInfo
   { piPieceLength  :: {-# UNPACK #-} !PieceSize
@@ -189,6 +194,9 @@ makeLensesFor [("piPieceHashes", "pieceHashes")] ''PieceInfo
 
 instance NFData PieceInfo
 
+instance Default PieceInfo where
+  def = PieceInfo 1 def
+
 instance Lint PieceInfo where
   lint pinfo @ PieceInfo {..}
     | BS.length (unHashList piPieceHashes) `rem` hashsize == 0