root / src / Ganeti / Utils.hs @ 72747d91
History | View | Annotate | Download (12.7 kB)
1 |
{-| Utility functions. -} |
---|---|
2 |
|
3 |
{- |
4 |
|
5 |
Copyright (C) 2009, 2010, 2011, 2012, 2013 Google Inc. |
6 |
|
7 |
This program is free software; you can redistribute it and/or modify |
8 |
it under the terms of the GNU General Public License as published by |
9 |
the Free Software Foundation; either version 2 of the License, or |
10 |
(at your option) any later version. |
11 |
|
12 |
This program is distributed in the hope that it will be useful, but |
13 |
WITHOUT ANY WARRANTY; without even the implied warranty of |
14 |
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
15 |
General Public License for more details. |
16 |
|
17 |
You should have received a copy of the GNU General Public License |
18 |
along with this program; if not, write to the Free Software |
19 |
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA |
20 |
02110-1301, USA. |
21 |
|
22 |
-} |
23 |
|
24 |
module Ganeti.Utils |
25 |
( debug |
26 |
, debugFn |
27 |
, debugXy |
28 |
, sepSplit |
29 |
, stdDev |
30 |
, if' |
31 |
, select |
32 |
, applyIf |
33 |
, commaJoin |
34 |
, ensureQuoted |
35 |
, tryRead |
36 |
, formatTable |
37 |
, printTable |
38 |
, parseUnit |
39 |
, plural |
40 |
, niceSort |
41 |
, niceSortKey |
42 |
, exitIfBad |
43 |
, exitErr |
44 |
, exitWhen |
45 |
, exitUnless |
46 |
, rStripSpace |
47 |
, newUUID |
48 |
, getCurrentTime |
49 |
, getCurrentTimeUSec |
50 |
, clockTimeToString |
51 |
, chompPrefix |
52 |
, wrap |
53 |
, trim |
54 |
, defaultHead |
55 |
, exitIfEmpty |
56 |
) where |
57 |
|
58 |
import Data.Char (toUpper, isAlphaNum, isDigit, isSpace) |
59 |
import Data.Function (on) |
60 |
import Data.List |
61 |
|
62 |
import Debug.Trace |
63 |
|
64 |
import Ganeti.BasicTypes |
65 |
import qualified Ganeti.Constants as C |
66 |
import System.IO |
67 |
import System.Exit |
68 |
import System.Time |
69 |
|
70 |
-- * Debug functions |
71 |
|
72 |
-- | To be used only for debugging, breaks referential integrity. |
73 |
debug :: Show a => a -> a |
74 |
debug x = trace (show x) x |
75 |
|
76 |
-- | Displays a modified form of the second parameter before returning |
77 |
-- it. |
78 |
debugFn :: Show b => (a -> b) -> a -> a |
79 |
debugFn fn x = debug (fn x) `seq` x |
80 |
|
81 |
-- | Show the first parameter before returning the second one. |
82 |
debugXy :: Show a => a -> b -> b |
83 |
debugXy = seq . debug |
84 |
|
85 |
-- * Miscellaneous |
86 |
|
87 |
-- | Apply the function if condition holds, otherwise use default value. |
88 |
applyIf :: Bool -> (a -> a) -> a -> a |
89 |
applyIf b f x = if b then f x else x |
90 |
|
91 |
-- | Comma-join a string list. |
92 |
commaJoin :: [String] -> String |
93 |
commaJoin = intercalate "," |
94 |
|
95 |
-- | Split a list on a separator and return an array. |
96 |
sepSplit :: Eq a => a -> [a] -> [[a]] |
97 |
sepSplit sep s |
98 |
| null s = [] |
99 |
| null xs = [x] |
100 |
| null ys = [x,[]] |
101 |
| otherwise = x:sepSplit sep ys |
102 |
where (x, xs) = break (== sep) s |
103 |
ys = drop 1 xs |
104 |
|
105 |
-- | Simple pluralize helper |
106 |
plural :: Int -> String -> String -> String |
107 |
plural 1 s _ = s |
108 |
plural _ _ p = p |
109 |
|
110 |
-- | Ensure a value is quoted if needed. |
111 |
ensureQuoted :: String -> String |
112 |
ensureQuoted v = if not (all (\c -> isAlphaNum c || c == '.') v) |
113 |
then '\'':v ++ "'" |
114 |
else v |
115 |
|
116 |
-- * Mathematical functions |
117 |
|
118 |
-- Simple and slow statistical functions, please replace with better |
119 |
-- versions |
120 |
|
121 |
-- | Standard deviation function. |
122 |
stdDev :: [Double] -> Double |
123 |
stdDev lst = |
124 |
-- first, calculate the list length and sum lst in a single step, |
125 |
-- for performance reasons |
126 |
let (ll', sx) = foldl' (\(rl, rs) e -> |
127 |
let rl' = rl + 1 |
128 |
rs' = rs + e |
129 |
in rl' `seq` rs' `seq` (rl', rs')) (0::Int, 0) lst |
130 |
ll = fromIntegral ll'::Double |
131 |
mv = sx / ll |
132 |
av = foldl' (\accu em -> let d = em - mv in accu + d * d) 0.0 lst |
133 |
in sqrt (av / ll) -- stddev |
134 |
|
135 |
-- * Logical functions |
136 |
|
137 |
-- Avoid syntactic sugar and enhance readability. These functions are proposed |
138 |
-- by some for inclusion in the Prelude, and at the moment they are present |
139 |
-- (with various definitions) in the utility-ht package. Some rationale and |
140 |
-- discussion is available at <http://www.haskell.org/haskellwiki/If-then-else> |
141 |
|
142 |
-- | \"if\" as a function, rather than as syntactic sugar. |
143 |
if' :: Bool -- ^ condition |
144 |
-> a -- ^ \"then\" result |
145 |
-> a -- ^ \"else\" result |
146 |
-> a -- ^ \"then\" or "else" result depending on the condition |
147 |
if' True x _ = x |
148 |
if' _ _ y = y |
149 |
|
150 |
-- * Parsing utility functions |
151 |
|
152 |
-- | Parse results from readsPrec. |
153 |
parseChoices :: (Monad m, Read a) => String -> String -> [(a, String)] -> m a |
154 |
parseChoices _ _ ((v, ""):[]) = return v |
155 |
parseChoices name s ((_, e):[]) = |
156 |
fail $ name ++ ": leftover characters when parsing '" |
157 |
++ s ++ "': '" ++ e ++ "'" |
158 |
parseChoices name s _ = fail $ name ++ ": cannot parse string '" ++ s ++ "'" |
159 |
|
160 |
-- | Safe 'read' function returning data encapsulated in a Result. |
161 |
tryRead :: (Monad m, Read a) => String -> String -> m a |
162 |
tryRead name s = parseChoices name s $ reads s |
163 |
|
164 |
-- | Format a table of strings to maintain consistent length. |
165 |
formatTable :: [[String]] -> [Bool] -> [[String]] |
166 |
formatTable vals numpos = |
167 |
let vtrans = transpose vals -- transpose, so that we work on rows |
168 |
-- rather than columns |
169 |
mlens = map (maximum . map length) vtrans |
170 |
expnd = map (\(flds, isnum, ml) -> |
171 |
map (\val -> |
172 |
let delta = ml - length val |
173 |
filler = replicate delta ' ' |
174 |
in if delta > 0 |
175 |
then if isnum |
176 |
then filler ++ val |
177 |
else val ++ filler |
178 |
else val |
179 |
) flds |
180 |
) (zip3 vtrans numpos mlens) |
181 |
in transpose expnd |
182 |
|
183 |
-- | Constructs a printable table from given header and rows |
184 |
printTable :: String -> [String] -> [[String]] -> [Bool] -> String |
185 |
printTable lp header rows isnum = |
186 |
unlines . map ((++) lp . (:) ' ' . unwords) $ |
187 |
formatTable (header:rows) isnum |
188 |
|
189 |
-- | Converts a unit (e.g. m or GB) into a scaling factor. |
190 |
parseUnitValue :: (Monad m) => String -> m Rational |
191 |
parseUnitValue unit |
192 |
-- binary conversions first |
193 |
| null unit = return 1 |
194 |
| unit == "m" || upper == "MIB" = return 1 |
195 |
| unit == "g" || upper == "GIB" = return kbBinary |
196 |
| unit == "t" || upper == "TIB" = return $ kbBinary * kbBinary |
197 |
-- SI conversions |
198 |
| unit == "M" || upper == "MB" = return mbFactor |
199 |
| unit == "G" || upper == "GB" = return $ mbFactor * kbDecimal |
200 |
| unit == "T" || upper == "TB" = return $ mbFactor * kbDecimal * kbDecimal |
201 |
| otherwise = fail $ "Unknown unit '" ++ unit ++ "'" |
202 |
where upper = map toUpper unit |
203 |
kbBinary = 1024 :: Rational |
204 |
kbDecimal = 1000 :: Rational |
205 |
decToBin = kbDecimal / kbBinary -- factor for 1K conversion |
206 |
mbFactor = decToBin * decToBin -- twice the factor for just 1K |
207 |
|
208 |
-- | Tries to extract number and scale from the given string. |
209 |
-- |
210 |
-- Input must be in the format NUMBER+ SPACE* [UNIT]. If no unit is |
211 |
-- specified, it defaults to MiB. Return value is always an integral |
212 |
-- value in MiB. |
213 |
parseUnit :: (Monad m, Integral a, Read a) => String -> m a |
214 |
parseUnit str = |
215 |
-- TODO: enhance this by splitting the unit parsing code out and |
216 |
-- accepting floating-point numbers |
217 |
case (reads str::[(Int, String)]) of |
218 |
[(v, suffix)] -> |
219 |
let unit = dropWhile (== ' ') suffix |
220 |
in do |
221 |
scaling <- parseUnitValue unit |
222 |
return $ truncate (fromIntegral v * scaling) |
223 |
_ -> fail $ "Can't parse string '" ++ str ++ "'" |
224 |
|
225 |
-- | Unwraps a 'Result', exiting the program if it is a 'Bad' value, |
226 |
-- otherwise returning the actual contained value. |
227 |
exitIfBad :: String -> Result a -> IO a |
228 |
exitIfBad msg (Bad s) = exitErr (msg ++ ": " ++ s) |
229 |
exitIfBad _ (Ok v) = return v |
230 |
|
231 |
-- | Exits immediately with an error message. |
232 |
exitErr :: String -> IO a |
233 |
exitErr errmsg = do |
234 |
hPutStrLn stderr $ "Error: " ++ errmsg |
235 |
exitWith (ExitFailure 1) |
236 |
|
237 |
-- | Exits with an error message if the given boolean condition if true. |
238 |
exitWhen :: Bool -> String -> IO () |
239 |
exitWhen True msg = exitErr msg |
240 |
exitWhen False _ = return () |
241 |
|
242 |
-- | Exits with an error message /unless/ the given boolean condition |
243 |
-- if true, the opposite of 'exitWhen'. |
244 |
exitUnless :: Bool -> String -> IO () |
245 |
exitUnless cond = exitWhen (not cond) |
246 |
|
247 |
-- | Helper for 'niceSort'. Computes the key element for a given string. |
248 |
extractKey :: [Either Integer String] -- ^ Current (partial) key, reversed |
249 |
-> String -- ^ Remaining string |
250 |
-> ([Either Integer String], String) |
251 |
extractKey ek [] = (reverse ek, []) |
252 |
extractKey ek xs@(x:_) = |
253 |
let (span_fn, conv_fn) = if isDigit x |
254 |
then (isDigit, Left . read) |
255 |
else (not . isDigit, Right) |
256 |
(k, rest) = span span_fn xs |
257 |
in extractKey (conv_fn k:ek) rest |
258 |
|
259 |
{-| Sort a list of strings based on digit and non-digit groupings. |
260 |
|
261 |
Given a list of names @['a1', 'a10', 'a11', 'a2']@ this function |
262 |
will sort the list in the logical order @['a1', 'a2', 'a10', 'a11']@. |
263 |
|
264 |
The sort algorithm breaks each name in groups of either only-digits or |
265 |
no-digits, and sorts based on each group. |
266 |
|
267 |
Internally, this is not implemented via regexes (like the Python |
268 |
version), but via actual splitting of the string in sequences of |
269 |
either digits or everything else, and converting the digit sequences |
270 |
in /Left Integer/ and the non-digit ones in /Right String/, at which |
271 |
point sorting becomes trivial due to the built-in 'Either' ordering; |
272 |
we only need one extra step of dropping the key at the end. |
273 |
|
274 |
-} |
275 |
niceSort :: [String] -> [String] |
276 |
niceSort = niceSortKey id |
277 |
|
278 |
-- | Key-version of 'niceSort'. We use 'sortBy' and @compare `on` fst@ |
279 |
-- since we don't want to add an ordering constraint on the /a/ type, |
280 |
-- hence the need to only compare the first element of the /(key, a)/ |
281 |
-- tuple. |
282 |
niceSortKey :: (a -> String) -> [a] -> [a] |
283 |
niceSortKey keyfn = |
284 |
map snd . sortBy (compare `on` fst) . |
285 |
map (\s -> (fst . extractKey [] $ keyfn s, s)) |
286 |
|
287 |
-- | Strip space characthers (including newline). As this is |
288 |
-- expensive, should only be run on small strings. |
289 |
rStripSpace :: String -> String |
290 |
rStripSpace = reverse . dropWhile isSpace . reverse |
291 |
|
292 |
-- | Returns a random UUID. |
293 |
-- This is a Linux-specific method as it uses the /proc filesystem. |
294 |
newUUID :: IO String |
295 |
newUUID = do |
296 |
contents <- readFile C.randomUuidFile |
297 |
return $! rStripSpace $ take 128 contents |
298 |
|
299 |
-- | Returns the current time as an 'Integer' representing the number |
300 |
-- of seconds from the Unix epoch. |
301 |
getCurrentTime :: IO Integer |
302 |
getCurrentTime = do |
303 |
TOD ctime _ <- getClockTime |
304 |
return ctime |
305 |
|
306 |
-- | Returns the current time as an 'Integer' representing the number |
307 |
-- of microseconds from the Unix epoch (hence the need for 'Integer'). |
308 |
getCurrentTimeUSec :: IO Integer |
309 |
getCurrentTimeUSec = do |
310 |
TOD ctime pico <- getClockTime |
311 |
-- pico: 10^-12, micro: 10^-6, so we have to shift seconds left and |
312 |
-- picoseconds right |
313 |
return $ ctime * 1000000 + pico `div` 1000000 |
314 |
|
315 |
-- | Convert a ClockTime into a (seconds-only) timestamp. |
316 |
clockTimeToString :: ClockTime -> String |
317 |
clockTimeToString (TOD t _) = show t |
318 |
|
319 |
{-| Strip a prefix from a string, allowing the last character of the prefix |
320 |
(which is assumed to be a separator) to be absent from the string if the string |
321 |
terminates there. |
322 |
|
323 |
>>> chompPrefix "foo:bar:" "a:b:c" |
324 |
Nothing |
325 |
|
326 |
>>> chompPrefix "foo:bar:" "foo:bar:baz" |
327 |
Just "baz" |
328 |
|
329 |
>>> chompPrefix "foo:bar:" "foo:bar:" |
330 |
Just "" |
331 |
|
332 |
>>> chompPrefix "foo:bar:" "foo:bar" |
333 |
Just "" |
334 |
|
335 |
>>> chompPrefix "foo:bar:" "foo:barbaz" |
336 |
Nothing |
337 |
-} |
338 |
chompPrefix :: String -> String -> Maybe String |
339 |
chompPrefix pfx str = |
340 |
if pfx `isPrefixOf` str || str == init pfx |
341 |
then Just $ drop (length pfx) str |
342 |
else Nothing |
343 |
|
344 |
-- | Breaks a string in lines with length \<= maxWidth. |
345 |
-- |
346 |
-- NOTE: The split is OK if: |
347 |
-- |
348 |
-- * It doesn't break a word, i.e. the next line begins with space |
349 |
-- (@isSpace . head $ rest@) or the current line ends with space |
350 |
-- (@null revExtra@); |
351 |
-- |
352 |
-- * It breaks a very big word that doesn't fit anyway (@null revLine@). |
353 |
wrap :: Int -- ^ maxWidth |
354 |
-> String -- ^ string that needs wrapping |
355 |
-> [String] -- ^ string \"broken\" in lines |
356 |
wrap maxWidth = filter (not . null) . map trim . wrap0 |
357 |
where wrap0 :: String -> [String] |
358 |
wrap0 text |
359 |
| length text <= maxWidth = [text] |
360 |
| isSplitOK = line : wrap0 rest |
361 |
| otherwise = line' : wrap0 rest' |
362 |
where (line, rest) = splitAt maxWidth text |
363 |
(revExtra, revLine) = break isSpace . reverse $ line |
364 |
(line', rest') = (reverse revLine, reverse revExtra ++ rest) |
365 |
isSplitOK = |
366 |
null revLine || null revExtra || startsWithSpace rest |
367 |
startsWithSpace (x:_) = isSpace x |
368 |
startsWithSpace _ = False |
369 |
|
370 |
-- | Removes surrounding whitespace. Should only be used in small |
371 |
-- strings. |
372 |
trim :: String -> String |
373 |
trim = reverse . dropWhile isSpace . reverse . dropWhile isSpace |
374 |
|
375 |
-- | A safer head version, with a default value. |
376 |
defaultHead :: a -> [a] -> a |
377 |
defaultHead def [] = def |
378 |
defaultHead _ (x:_) = x |
379 |
|
380 |
-- | A 'head' version in the I/O monad, for validating parameters |
381 |
-- without which we cannot continue. |
382 |
exitIfEmpty :: String -> [a] -> IO a |
383 |
exitIfEmpty _ (x:_) = return x |
384 |
exitIfEmpty s [] = exitErr s |