diff --git a/LICENSE b/LICENSE
new file mode 100644
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,29 @@
+Copyright (c) 2013, IIJ Innovation Institute Inc.
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions
+are met:
+
+  * Redistributions of source code must retain the above copyright
+    notice, this list of conditions and the following disclaimer.
+  * Redistributions in binary form must reproduce the above copyright
+    notice, this list of conditions and the following disclaimer in
+    the documentation and/or other materials provided with the
+    distribution.
+  * Neither the name of the copyright holders nor the names of its
+    contributors may be used to endorse or promote products derived
+    from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGE.
diff --git a/Network/SockAddr.hs b/Network/SockAddr.hs
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--- /dev/null
+++ b/Network/SockAddr.hs
@@ -0,0 +1,76 @@
+-- | Converting an address in 'SockAddr'.
+
+module Network.SockAddr (
+    showSockAddr
+  , showSockAddrBS
+  ) where
+
+import Data.Bits (shift, (.&.))
+import Data.ByteString (ByteString)
+import qualified Data.ByteString.Char8 as BS (pack)
+import Network.Socket (SockAddr(..), HostAddress, HostAddress6)
+import System.ByteOrder
+import Text.Printf
+
+isReversed :: Bool
+isReversed = byteOrder == LittleEndian
+
+----------------------------------------------------------------
+
+-- | Convert 'SockAddr' to 'String'. If the address is
+--   an IPv4-embedded IPv6 address, the IPv4 is extracted.
+--
+-- >>> import Network.Socket
+-- >>> as <- getAddrInfo (Just defaultHints) (Just "example.org") (Just "http")
+-- >>> map (showSockAddr.addrAddress) as
+-- ["93.184.216.119","93.184.216.119","2606:2800:220:6d:26bf:1447:1097:aa7","2606:2800:220:6d:26bf:1447:1097:aa7"]
+showSockAddr :: SockAddr -> String
+showSockAddr (SockAddrInet _ addr4)                       = showIPv4 addr4 isReversed
+showSockAddr (SockAddrInet6 _ _ (0,0,0x0000ffff,addr4) _) = showIPv4 addr4 False
+showSockAddr (SockAddrInet6 _ _ (0,0,0,1) _)              = "::1"
+showSockAddr (SockAddrInet6 _ _ addr6 _)                  = showIPv6 addr6
+showSockAddr _                                            = "unknownSocket"
+
+----------------------------------------------------------------
+
+-- HostAddress is network byte order.
+showIPv4 :: HostAddress -> Bool-> String
+showIPv4 w32 reversed
+  | reversed  = show b1 ++ "." ++ show b2 ++ "." ++ show b3 ++ "." ++ show b4
+  | otherwise = show b4 ++ "." ++ show b3 ++ "." ++ show b2 ++ "." ++ show b1
+  where
+    t1 = w32
+    t2 = shift t1 (-8)
+    t3 = shift t2 (-8)
+    t4 = shift t3 (-8)
+    b1 = t1 .&. 0x000000ff
+    b2 = t2 .&. 0x000000ff
+    b3 = t3 .&. 0x000000ff
+    b4 = t4 .&. 0x000000ff
+
+-- HostAddress6 is host byte order.
+showIPv6 :: HostAddress6 -> String
+showIPv6 (w1,w2,w3,w4) =
+    printf "%x:%x:%x:%x:%x:%x:%x:%x" s1 s2 s3 s4 s5 s6 s7 s8
+  where
+    (s1,s2) = split16 w1
+    (s3,s4) = split16 w2
+    (s5,s6) = split16 w3
+    (s7,s8) = split16 w4
+    split16 w = (h1,h2)
+      where
+        h1 = shift w (-16) .&. 0x0000ffff
+        h2 = w .&. 0x0000ffff
+
+----------------------------------------------------------------
+
+-- | Convert 'SockAddr' to 'ByteString'. If the address is
+--   an IPv4-embedded IPv6 address, the IPv4 is extracted.
+--
+-- >>> import Network.Socket
+-- >>> as <- getAddrInfo (Just defaultHints) (Just "localhost") (Just "http")
+-- >>> map (showSockAddrBS.addrAddress) as
+-- ["127.0.0.1","::1","fe80:0:0:0:0:0:0:1"]
+
+showSockAddrBS :: SockAddr -> ByteString
+showSockAddrBS = BS.pack . showSockAddr
diff --git a/Setup.hs b/Setup.hs
new file mode 100644
--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/sockaddr.cabal b/sockaddr.cabal
new file mode 100644
--- /dev/null
+++ b/sockaddr.cabal
@@ -0,0 +1,24 @@
+Name:                   sockaddr
+Version:                0.0.0
+Author:                 Kazu Yamamoto <kazu@iij.ad.jp>
+Maintainer:             Kazu Yamamoto <kazu@iij.ad.jp>
+License:                BSD3
+License-File:           LICENSE
+Synopsis:               Printing SockAddr
+Description:            Printing SockAddr
+Category:               Network
+Cabal-Version:          >= 1.10
+Build-Type:             Simple
+
+Library
+  Default-Language:     Haskell2010
+  GHC-Options:          -Wall
+  Exposed-Modules:      Network.SockAddr
+  Build-Depends:        base >= 4 && < 5
+                      , byteorder
+                      , bytestring
+                      , network
+
+Source-Repository head
+  Type:                 git
+  Location:             git://github.com/kazu-yamamoto/sockaddr