90 lines
2.3 KiB
Haskell
90 lines
2.3 KiB
Haskell
{- Simple line-based protocols.
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-
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- Copyright 2013-2014 Joey Hess <id@joeyh.name>
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-
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- License: BSD-2-clause
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-}
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module Utility.SimpleProtocol (
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Sendable(..),
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Receivable(..),
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parseMessage,
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Serializable(..),
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Parser,
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parseFail,
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parse0,
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parse1,
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parse2,
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parse3,
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dupIoHandles,
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) where
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import Data.Char
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import GHC.IO.Handle
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import Common
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-- Messages that can be sent.
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class Sendable m where
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formatMessage :: m -> [String]
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-- Messages that can be received.
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class Receivable m where
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-- Passed the first word of the message, returns
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-- a Parser that can be be fed the rest of the message to generate
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-- the value.
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parseCommand :: String -> Parser m
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parseMessage :: (Receivable m) => String -> Maybe m
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parseMessage s = parseCommand command rest
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where
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(command, rest) = splitWord s
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class Serializable a where
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serialize :: a -> String
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deserialize :: String -> Maybe a
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{- Parsing the parameters of messages. Using the right parseN ensures
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- that the string is split into exactly the requested number of words,
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- which allows the last parameter of a message to contain arbitrary
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- whitespace, etc, without needing any special quoting.
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-}
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type Parser a = String -> Maybe a
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parseFail :: Parser a
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parseFail _ = Nothing
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parse0 :: a -> Parser a
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parse0 mk "" = Just mk
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parse0 _ _ = Nothing
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parse1 :: Serializable p1 => (p1 -> a) -> Parser a
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parse1 mk p1 = mk <$> deserialize p1
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parse2 :: (Serializable p1, Serializable p2) => (p1 -> p2 -> a) -> Parser a
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parse2 mk s = mk <$> deserialize p1 <*> deserialize p2
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where
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(p1, p2) = splitWord s
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parse3 :: (Serializable p1, Serializable p2, Serializable p3) => (p1 -> p2 -> p3 -> a) -> Parser a
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parse3 mk s = mk <$> deserialize p1 <*> deserialize p2 <*> deserialize p3
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where
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(p1, rest) = splitWord s
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(p2, p3) = splitWord rest
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splitWord :: String -> (String, String)
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splitWord = separate isSpace
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{- When a program speaks a simple protocol over stdio, any other output
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- to stdout (or anything that attempts to read from stdin)
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- will mess up the protocol. To avoid that, close stdin,
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- and duplicate stderr to stdout. Return two new handles
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- that are duplicates of the original (stdin, stdout). -}
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dupIoHandles :: IO (Handle, Handle)
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dupIoHandles = do
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readh <- hDuplicate stdin
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writeh <- hDuplicate stdout
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nullh <- openFile devNull ReadMode
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nullh `hDuplicateTo` stdin
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stderr `hDuplicateTo` stdout
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return (readh, writeh)
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