Text loader: split parsing from loadData

This change, which will be followed by similar changes in the other
loaders, splits the parsing of the data from the actual loading from
disk. Since the parsing doesn't usually involve IO actions, we will be
able to better test the parsing. The loading becomes a smaller part of
the code and thus inability to test it has a smaller impact.

Ganeti/HTools/Text.hs

@@ -29,6 +29,7 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 module Ganeti.HTools.Text
     (
       loadData
+    , parseData
     , loadInst
     , loadNode
     , serializeInstances
@@ -136,19 +137,27 @@ loadTabular lines_data convert_fn = do
   kerows <- mapM convert_fn rows
   return $ assignIndices kerows
 
+-- | Load the cluser data from disk.
+readData :: String -- ^ Path to the text file
+         -> IO String
+readData = readFile
+
 -- | Builds the cluster data from text input.
-loadData :: String -- ^ Path to the text file
-         -> IO (Result (Node.AssocList, Instance.AssocList, [String]))
-loadData afile = do -- IO monad
-  fdata <- readFile afile
+parseData :: String -- ^ Text data
+          -> Result (Node.AssocList, Instance.AssocList, [String])
+parseData fdata = do
   let flines = lines fdata
       (nlines, ilines) = break null flines
-  return $ do
-    ifixed <- case ilines of
-                [] -> Bad "Invalid format of the input file (no instance data)"
-                _:xs -> Ok xs
-    {- node file: name t_mem n_mem f_mem t_disk f_disk -}
-    (ktn, nl) <- loadTabular nlines loadNode
-    {- instance file: name mem disk status pnode snode -}
-    (_, il) <- loadTabular ifixed (loadInst ktn)
-    return (nl, il, [])
+  ifixed <- case ilines of
+    [] -> Bad "Invalid format of the input file (no instance data)"
+    _:xs -> Ok xs
+  {- node file: name t_mem n_mem f_mem t_disk f_disk -}
+  (ktn, nl) <- loadTabular nlines loadNode
+  {- instance file: name mem disk status pnode snode -}
+  (_, il) <- loadTabular ifixed (loadInst ktn)
+  return (nl, il, [])
+
+-- | Top level function for data loading
+loadData :: String -- ^ Path to the text file
+         -> IO (Result (Node.AssocList, Instance.AssocList, [String]))
+loadData afile = readData afile >>= return . parseData