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  • Iustin Pop's avatar
    Enhance the error reporting for Rapi and Luxi · 117dc2d8
    Iustin Pop authored
    Currently the JSON conversion in Rapi and Luxi are giving something
    like:
      Error: failed to load data. Details:
      Unable to read Double
    
    This doesn't tell one where the error is (in a node specification? and
    which node? etc.). This patch annotates such messages with the owner
    node:
      Error: failed to load data. Details:
      Node 'node1' key 'mtotal': Unable to read Double
    
    For errors during parsing of the node/instance name (unlikely, but
    still), the output is:
      Error: failed to load data. Details:
      Parsing new node key 'name': Unable to read String
    117dc2d8
Utils.hs 5.75 KiB
{-| Utility functions -}

{-

Copyright (C) 2009 Google Inc.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301, USA.

-}

module Ganeti.HTools.Utils
    (
      debug
    , sepSplit
    , fst3
    , varianceCoeff
    , commaJoin
    , readEitherString
    , loadJSArray
    , fromObj
    , tryFromObj
    , fromJVal
    , asJSObject
    , asObjectList
    , fromJResult
    , tryRead
    , formatTable
    , annotateResult
    ) where

import Data.List
import Control.Monad
import qualified Text.JSON as J
import Text.Printf (printf)

import Debug.Trace

import Ganeti.HTools.Types

-- * Debug functions

-- | To be used only for debugging, breaks referential integrity.
debug :: Show a => a -> a
debug x = trace (show x) x

-- * Miscelaneous

-- | Comma-join a string list.
commaJoin :: [String] -> String
commaJoin = intercalate ","

-- | Split a string on a separator and return an array.
sepSplit :: Char -> String -> [String]
sepSplit sep s
    | x == "" && xs == [] = []
    | xs == []            = [x]
    | ys == []            = [x,""]
    | otherwise           = x:sepSplit sep ys
    where (x, xs) = break (== sep) s
          ys = drop 1 xs

-- | Simple version of 'fst' for a triple
fst3 :: (a, b, c) -> a
fst3 (a, _, _) = a

-- * Mathematical functions

-- Simple and slow statistical functions, please replace with better versions

-- | Mean value of a list.
meanValue :: Floating a => [a] -> a
meanValue lst = sum lst / fromIntegral (length lst)

-- | Standard deviation.
stdDev :: Floating a => [a] -> a
stdDev lst =
    let mv = meanValue lst
        av = foldl' (\accu em -> let d = em - mv in accu + d * d) 0.0 lst
        bv = sqrt (av / fromIntegral (length lst))
    in bv

-- | Coefficient of variation.
varianceCoeff :: Floating a => [a] -> a
varianceCoeff lst = stdDev lst / fromIntegral (length lst)

-- * JSON-related functions

-- | Converts a JSON Result into a monadic value.
fromJResult :: Monad m => J.Result a -> m a
fromJResult (J.Error x) = fail x
fromJResult (J.Ok x) = return x

-- | Tries to read a string from a JSON value.
--
-- In case the value was not a string, we fail the read (in the
-- context of the current monad.
readEitherString :: (Monad m) => J.JSValue -> m String
readEitherString v =
    case v of
      J.JSString s -> return $ J.fromJSString s
      _ -> fail "Wrong JSON type"

-- | Converts a JSON message into an array of JSON objects.
loadJSArray :: (Monad m) => String -> m [J.JSObject J.JSValue]
loadJSArray = fromJResult . J.decodeStrict

-- | Reads a the value of a key in a JSON object.
fromObj :: (J.JSON a, Monad m) => String -> [(String, J.JSValue)] -> m a
fromObj k o =
    case lookup k o of
      Nothing -> fail $ printf "key '%s' not found in %s" k (show o)
      Just val -> fromJResult $ J.readJSON val

-- | Annotate a Result with an ownership information
annotateResult :: String -> Result a -> Result a
annotateResult owner (Bad s) = Bad $ owner ++ ": " ++ s
annotateResult _ v = v

-- | Try to extract a key from a object with better error reporting
-- than fromObj
tryFromObj :: (J.JSON a) =>
              String -> [(String, J.JSValue)] -> String -> Result a
tryFromObj t o k = annotateResult (t ++ " key '" ++ k ++ "'") (fromObj k o)

-- | Small wrapper over readJSON.
fromJVal :: (Monad m, J.JSON a) => J.JSValue -> m a
fromJVal v =
    case J.readJSON v of
      J.Error s -> fail ("Cannot convert value " ++ show v ++ ", error: " ++ s)
      J.Ok x -> return x

-- | Converts a JSON value into a JSON object.
asJSObject :: (Monad m) => J.JSValue -> m (J.JSObject J.JSValue)
asJSObject (J.JSObject a) = return a
asJSObject _ = fail "not an object"

-- | Coneverts a list of JSON values into a list of JSON objects.
asObjectList :: (Monad m) => [J.JSValue] -> m [J.JSObject J.JSValue]
asObjectList = mapM asJSObject

-- * Parsing utility functions

-- | Parse results from readsPrec
parseChoices :: (Monad m, Read a) => String -> String -> [(a, String)] -> m a
parseChoices _ _ ((v, ""):[]) = return v
parseChoices name s ((_, e):[]) =
    fail $ name ++ ": leftover characters when parsing '"
           ++ s ++ "': '" ++ e ++ "'"
parseChoices name s _ = fail $ name ++ ": cannot parse string '" ++ s ++ "'"

-- | Safe 'read' function returning data encapsulated in a Result.
tryRead :: (Monad m, Read a) => String -> String -> m a
tryRead name s = parseChoices name s $ reads s

-- | Format a table of strings to maintain consistent length
formatTable :: [[String]] -> [Bool] -> [[String]]
formatTable vals numpos =
    let vtrans = transpose vals  -- transpose, so that we work on rows
                                 -- rather than columns
        mlens = map (maximum . map length) vtrans
        expnd = map (\(flds, isnum, ml) ->
                         map (\val ->
                                  let delta = ml - length val
                                      filler = replicate delta ' '
                                  in if delta > 0
                                     then if isnum
                                          then filler ++ val
                                          else val ++ filler
                                     else val
                             ) flds
                    ) (zip3 vtrans numpos mlens)
   in transpose expnd