git-annex/Utility/SimpleProtocol.hs
Joey Hess aa1ad0b7ca
remove redundant imports
Clean build under ghc 8.8.3, which seems to do better at finding cases
where two imports both provide the same symbol, and warns about one of
them.

This commit was sponsored by Ilya Shlyakhter on Patreon.
2020-06-22 11:05:34 -04:00

129 lines
3.4 KiB
Haskell

{- Simple line-based protocols.
-
- Copyright 2013-2016 Joey Hess <id@joeyh.name>
-
- License: BSD-2-clause
-}
{-# LANGUAGE FlexibleInstances #-}
{-# OPTIONS_GHC -fno-warn-orphans #-}
module Utility.SimpleProtocol (
Sendable(..),
Receivable(..),
parseMessage,
Serializable(..),
Parser,
parseFail,
parse0,
parse1,
parse2,
parse3,
dupIoHandles,
getProtocolLine,
) where
import Data.Char
import GHC.IO.Handle
import Common
-- Messages that can be sent.
class Sendable m where
formatMessage :: m -> [String]
-- Messages that can be received.
class Receivable m where
-- Passed the first word of the message, returns
-- a Parser that can be be fed the rest of the message to generate
-- the value.
parseCommand :: String -> Parser m
parseMessage :: (Receivable m) => String -> Maybe m
parseMessage s = parseCommand command rest
where
(command, rest) = splitWord s
class Serializable a where
serialize :: a -> String
deserialize :: String -> Maybe a
instance Serializable [Char] where
serialize = id
deserialize = Just
instance Serializable ExitCode where
serialize ExitSuccess = "0"
serialize (ExitFailure n) = show n
deserialize "0" = Just ExitSuccess
deserialize s = ExitFailure <$> readish s
{- Parsing the parameters of messages. Using the right parseN ensures
- that the string is split into exactly the requested number of words,
- which allows the last parameter of a message to contain arbitrary
- whitespace, etc, without needing any special quoting.
-}
type Parser a = String -> Maybe a
parseFail :: Parser a
parseFail _ = Nothing
parse0 :: a -> Parser a
parse0 mk "" = Just mk
parse0 _ _ = Nothing
parse1 :: Serializable p1 => (p1 -> a) -> Parser a
parse1 mk p1 = mk <$> deserialize p1
parse2 :: (Serializable p1, Serializable p2) => (p1 -> p2 -> a) -> Parser a
parse2 mk s = mk <$> deserialize p1 <*> deserialize p2
where
(p1, p2) = splitWord s
parse3 :: (Serializable p1, Serializable p2, Serializable p3) => (p1 -> p2 -> p3 -> a) -> Parser a
parse3 mk s = mk <$> deserialize p1 <*> deserialize p2 <*> deserialize p3
where
(p1, rest) = splitWord s
(p2, p3) = splitWord rest
splitWord :: String -> (String, String)
splitWord = separate isSpace
{- When a program speaks a simple protocol over stdio, any other output
- to stdout (or anything that attempts to read from stdin)
- will mess up the protocol. To avoid that, close stdin,
- and duplicate stderr to stdout. Return two new handles
- that are duplicates of the original (stdin, stdout). -}
dupIoHandles :: IO (Handle, Handle)
dupIoHandles = do
readh <- hDuplicate stdin
writeh <- hDuplicate stdout
nullh <- openFile devNull ReadMode
nullh `hDuplicateTo` stdin
stderr `hDuplicateTo` stdout
return (readh, writeh)
{- Reads a line, but to avoid super-long lines eating memory, returns
- Nothing if 32 kb have been read without seeing a '\n'
-
- If there is a '\r' before the '\n', it is removed, to support
- systems using "\r\n" at ends of lines
-
- This implementation is not super efficient, but as long as the Handle
- supports buffering, it avoids reading a character at a time at the
- syscall level.
-
- Throws isEOFError when no more input is available.
-}
getProtocolLine :: Handle -> IO (Maybe String)
getProtocolLine h = go (32768 :: Int) []
where
go 0 _ = return Nothing
go n l = do
c <- hGetChar h
if c == '\n'
then return $ Just $ reverse $
case l of
('\r':rest) -> rest
_ -> l
else go (n-1) (c:l)