1 files changed, 24 insertions, 0 deletions

diff --git a/src/Data/Torrent/InfoHash.hs b/src/Data/Torrent/InfoHash.hs
index 448e9a5a..b2ca44ee 100644
--- a/src/Data/Torrent/InfoHash.hs
+++ b/src/Data/Torrent/InfoHash.hs
@@ -1,5 +1,6 @@
 module Data.Torrent.InfoHash
        ( InfoHash (getInfoHash)
+       , addHashToURI
 
          -- ^ Construction
        , hash, hashlazy
@@ -10,6 +11,8 @@ module Data.Torrent.InfoHash
 
 import Control.Applicative
 import Data.Foldable
+import Data.List as L
+import Data.Char
 import           Data.ByteString (ByteString)
 import qualified Data.ByteString as B
 import qualified Data.ByteString.Char8 as BC
@@ -18,6 +21,9 @@ import qualified Data.ByteString.Builder.Prim as B
 import qualified Data.ByteString.Lazy as Lazy
 import Data.Serialize
 import qualified Crypto.Hash.SHA1 as C
+import Network.URI
+import Numeric
+
 
 -- | Exactly 20 bytes long SHA1 hash.
 newtype InfoHash = InfoHash { getInfoHash :: ByteString }
@@ -39,3 +45,21 @@ hashlazy = InfoHash . C.hashlazy
 ppHex :: InfoHash -> ByteString
 ppHex = Lazy.toStrict . B.toLazyByteString .
         foldMap (B.primFixed B.word8HexFixed) . B.unpack . getInfoHash
+
+addHashToURI :: URI -> InfoHash -> URI
+addHashToURI uri s = uri {
+    uriQuery = uriQuery uri ++ mkPref (uriQuery uri) ++
+               "info_hash=" ++ rfc1738Encode (BC.unpack (getInfoHash s))
+  }
+  where
+    mkPref [] = "?"
+    mkPref ('?' : _) = "&"
+    mkPref _ = error "addHashToURI"
+
+    rfc1738Encode = L.concatMap (\c -> if unreservedS c then [c] else encodeHex c)
+      where
+        unreservedS = (`L.elem` chars)
+        chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_./"
+        encodeHex c = '%' : pHex c
+        pHex c = let p = (showHex . ord $ c) ""
+                 in if L.length p == 1 then '0' : p else p