src/Ganeti/Hypervisor/Xen/XmParser.hs

{-# LANGUAGE OverloadedStrings #-}
{-| Parser for the output of the @xm list --long@ command of Xen

-}
{-

Copyright (C) 2013 Google Inc.
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PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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-}
module Ganeti.Hypervisor.Xen.XmParser
  ( xmListParser
  , lispConfigParser
  , xmUptimeParser
  , uptimeLineParser
  ) where

import Control.Applicative
import Control.Monad
import qualified Data.Attoparsec.Combinator as AC
import qualified Data.Attoparsec.Text as A
import Data.Attoparsec.Text (Parser)
import Data.Char
import Data.List
import Data.Text (unpack)
import qualified Data.Map as Map

import Ganeti.BasicTypes
import Ganeti.Hypervisor.Xen.Types

-- | A parser for parsing generic config files written in the (LISP-like)
-- format that is the output of the @xm list --long@ command.
-- This parser only takes care of the syntactic parse, but does not care
-- about the semantics.
-- Note: parsing the double requires checking for the next character in order
-- to prevent string like "9a" to be recognized as the number 9.
lispConfigParser :: Parser LispConfig
lispConfigParser =
  A.skipSpace *>
    (   listConfigP
    <|> doubleP
    <|> stringP
    )
  <* A.skipSpace
    where listConfigP = LCList <$> (A.char '(' *> liftA2 (++)
            (many middleP)
            (((:[]) <$> finalP) <|> (rparen *> pure [])))
          doubleP = LCDouble <$> A.rational <* A.skipSpace <* A.endOfInput
          innerDoubleP = LCDouble <$> A.rational
          stringP = LCString . unpack <$> A.takeWhile1 (not . (\c -> isSpace c
            || c `elem` "()"))
          wspace = AC.many1 A.space
          rparen = A.skipSpace *> A.char ')'
          finalP =   listConfigP <* rparen
                 <|> innerDoubleP <* rparen
                 <|> stringP <* rparen
          middleP =   listConfigP <* wspace
                  <|> innerDoubleP <* wspace
                  <|> stringP <* wspace


-- | Find a configuration having the given string as its first element,
-- from a list of configurations.
findConf :: String -> [LispConfig] -> Result LispConfig
findConf key configs =
  case find (isNamed key) configs of
    (Just c) -> Ok c
    _ -> Bad "Configuration not found"

-- | Get the value of of a configuration having the given string as its
-- first element.
-- The value is the content of the configuration, discarding the name itself.
getValue :: (FromLispConfig a) => String -> [LispConfig] -> Result a
getValue key configs = findConf key configs >>= fromLispConfig

-- | Extract the values of a configuration containing a list of them.
extractValues :: LispConfig -> Result [LispConfig]
extractValues c = tail `fmap` fromLispConfig c

-- | Verify whether the given configuration has a certain name or not.fmap
-- The name of a configuration is its first parameter, if it is a string.
isNamed :: String -> LispConfig -> Bool
isNamed key (LCList (LCString x:_)) = x == key
isNamed _ _ = False

-- | Parser for recognising the current state of a Xen domain.
parseState :: String -> ActualState
parseState s =
  case s of
    "r-----" -> ActualRunning
    "-b----" -> ActualBlocked
    "--p---" -> ActualPaused
    "---s--" -> ActualShutdown
    "----c-" -> ActualCrashed
    "-----d" -> ActualDying
    _ -> ActualUnknown

-- | Extract the configuration data of a Xen domain from a generic LispConfig
-- data structure. Fail if the LispConfig does not represent a domain.
getDomainConfig :: LispConfig -> Result Domain
getDomainConfig configData = do
  domainConf <-
    if isNamed "domain" configData
      then extractValues configData
      else Bad $ "Not a domain configuration: " ++ show configData
  domid <- getValue "domid" domainConf
  name <- getValue "name" domainConf
  cpuTime <- getValue "cpu_time" domainConf
  state <- getValue "state" domainConf
  let actualState = parseState state
  return $ Domain domid name cpuTime actualState Nothing

-- | A parser for parsing the output of the @xm list --long@ command.
-- It adds the semantic layer on top of lispConfigParser.
-- It returns a map of domains, with their name as the key.
-- FIXME: This is efficient under the assumption that only a few fields of the
-- domain configuration are actually needed. If many of them are required, a
-- parser able to directly extract the domain config would actually be better.
xmListParser :: Parser (Map.Map String Domain)
xmListParser = do
  configs <- lispConfigParser `AC.manyTill` A.endOfInput
  let domains = map getDomainConfig configs
      foldResult m (Ok val) = Ok $ Map.insert (domName val) val m
      foldResult _ (Bad msg) = Bad msg
  case foldM foldResult Map.empty domains of
    Ok d -> return d
    Bad msg -> fail msg

-- | A parser for parsing the output of the @xm uptime@ command.
xmUptimeParser :: Parser (Map.Map Int UptimeInfo)
xmUptimeParser = do
  _ <- headerParser
  uptimes <- uptimeLineParser `AC.manyTill` A.endOfInput
  return $ Map.fromList [(uInfoID u, u) | u <- uptimes]
    where headerParser = A.string "Name" <* A.skipSpace <* A.string "ID"
            <* A.skipSpace <* A.string "Uptime" <* A.skipSpace

-- | A helper for parsing a single line of the @xm uptime@ output.
uptimeLineParser :: Parser UptimeInfo
uptimeLineParser = do
  name <- A.takeTill isSpace <* A.skipSpace
  idNum <- A.decimal <* A.skipSpace
  uptime <- A.takeTill (`elem` "\n\r") <* A.skipSpace
  return . UptimeInfo (unpack name) idNum $ unpack uptime