Making getAddrInfo polymorphic

Network/Socket.hs

@@ -33,6 +33,7 @@
 -- > import qualified Control.Exception as E
 -- > import Control.Monad (unless, forever, void)
 -- > import qualified Data.ByteString as S
+-- > import qualified Data.List.NonEmpty as NE
 -- > import Network.Socket
 -- > import Network.Socket.ByteString (recv, sendAll)
 -- >
@@ -56,7 +57,7 @@
 -- >                 addrFlags = [AI_PASSIVE]
 -- >               , addrSocketType = Stream
 -- >               }
--- >         head <$> getAddrInfo (Just hints) mhost (Just port)
+-- >         NE.head <$> getAddrInfoNE (Just hints) mhost (Just port)
 -- >     open addr = E.bracketOnError (openSocket addr) close $ \sock -> do
 -- >         setSocketOption sock ReuseAddr 1
 -- >         withFdSocket sock setCloseOnExecIfNeeded
@@ -77,6 +78,7 @@
 -- >
 -- > import qualified Control.Exception as E
 -- > import qualified Data.ByteString.Char8 as C
+-- > import qualified Data.List.NonEmpty as NE
 -- > import Network.Socket
 -- > import Network.Socket.ByteString (recv, sendAll)
 -- >
@@ -95,7 +97,7 @@
 -- >   where
 -- >     resolve = do
 -- >         let hints = defaultHints { addrSocketType = Stream }
--- >         head <$> getAddrInfo (Just hints) (Just host) (Just port)
+-- >         NE.head <$> getAddrInfoNE (Just hints) (Just host) (Just port)
 -- >     open addr = E.bracketOnError (openSocket addr) close $ \sock -> do
 -- >         connect sock $ addrAddress addr
 -- >         return sock
@@ -111,6 +113,7 @@ module Network.Socket (
 
     -- * Address information
     getAddrInfo,
+    getAddrInfoNE,
 
     -- ** Types
     HostName,

Network/Socket/Info.hsc

@@ -7,6 +7,7 @@
 
 module Network.Socket.Info where
 
+import qualified Data.List.NonEmpty as NE
 import Foreign.Marshal.Alloc (alloca, allocaBytes)
 import Foreign.Marshal.Utils (maybeWith, with)
 import GHC.IO.Exception (IOErrorType(NoSuchThing))
@@ -290,6 +291,15 @@ getAddrInfo hints node service = alloc getaddrinfo
     filteredHints = hints
 #endif
 
+getAddrInfoNE
+    :: Maybe AddrInfo
+    -> Maybe HostName
+    -> Maybe ServiceName
+    -> IO (NE.NonEmpty AddrInfo)
+getAddrInfoNE hints node service =
+    -- getAddrInfo never returns an empty list.
+    NE.fromList <$> getAddrInfo hints node service
+
 followAddrInfo :: Ptr AddrInfo -> IO [AddrInfo]
 followAddrInfo ptr_ai
     | ptr_ai == nullPtr = return []

examples/EchoClient.hs

@@ -5,6 +5,7 @@ module Main (main) where
 
 import qualified Control.Exception as E
 import qualified Data.ByteString.Char8 as C
+import qualified Data.List.NonEmpty as NE
 import Network.Socket
 import Network.Socket.ByteString (recv, sendAll)
 
@@ -23,7 +24,7 @@ runTCPClient host port client = withSocketsDo $ do
   where
     resolve = do
         let hints = defaultHints{addrSocketType = Stream}
-        head <$> getAddrInfo (Just hints) (Just host) (Just port)
+        NE.head <$> getAddrInfoNE (Just hints) (Just host) (Just port)
     open addr = E.bracketOnError (openSocket addr) close $ \sock -> do
         connect sock $ addrAddress addr
         return sock

examples/EchoServer.hs

@@ -5,6 +5,7 @@ import Control.Concurrent (forkFinally)
 import qualified Control.Exception as E
 import Control.Monad (forever, unless, void)
 import qualified Data.ByteString as S
+import qualified Data.List.NonEmpty as NE
 import Network.Socket
 import Network.Socket.ByteString (recv, sendAll)
 
@@ -29,7 +30,7 @@ runTCPServer mhost port server = withSocketsDo $ do
                     { addrFlags = [AI_PASSIVE]
                     , addrSocketType = Stream
                     }
-        head <$> getAddrInfo (Just hints) mhost (Just port)
+        NE.head <$> getAddrInfoNE (Just hints) mhost (Just port)
     open addr = E.bracketOnError (openSocket addr) close $ \sock -> do
         setSocketOption sock ReuseAddr 1
         withFdSocket sock setCloseOnExecIfNeeded

tests/Network/Test/Common.hs

@@ -35,10 +35,11 @@
 import Control.Monad
 import Data.ByteString (ByteString)
 import qualified Data.ByteString.Lazy as L
+import qualified Data.List.NonEmpty as NE
 import Network.Socket
 import System.Directory
 import System.Timeout (timeout)
 import Test.Hspec
 
 serverAddr :: String
 serverAddr = "127.0.0.1"
@@ -244,7 +245,7 @@
 
 resolveClient :: SocketType -> HostName -> PortNumber -> IO AddrInfo
 resolveClient socketType host port =
-    head <$> getAddrInfo (Just hints) (Just host) (Just $ show port)
+    NE.head <$> getAddrInfoNE (Just hints) (Just host) (Just $ show port)
   where
     hints = defaultHints {
         addrSocketType = socketType
@@ -253,7 +254,7 @@
 
 resolveServer :: SocketType -> HostName -> IO AddrInfo
 resolveServer socketType host =
-    head <$> getAddrInfo (Just hints) (Just host) Nothing
+    NE.head <$> getAddrInfoNE (Just hints) (Just host) Nothing
   where
     hints = defaultHints {
         addrSocketType = socketType