NixConf.hs

{-# LANGUAGE DeriveFunctor #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}

{- (Very limited) parser, rendered and modifier of nix.conf

Supports subset of nix.conf given Nix 2.0 or Nix 1.0

When reading config files, it normalizes Nix 1.0/2.0 names to unified naming,
then when it writes the config back, it uses naming depending what given Nix
version considers as recommended.

-}
module Cachix.Client.NixConf
  ( NixConf,
    NixConfG (..),
    NixConfLine (..),
    NixConfLoc (..),
    render,
    add,
    read,
    update,
    write,
    getFilename,
    parser,
    parse,
    readLines,
    writeLines,
    isTrustedUsers,
    defaultPublicURI,
    defaultSigningKey,
    setNetRC
    )
where

import Cachix.Api (BinaryCache (..))
import Data.Char (isSpace)
import Data.List (nub)
import qualified Data.Text as T
import Protolude
import System.Directory
  ( XdgDirectory (..),
    createDirectoryIfMissing,
    doesFileExist,
    getXdgDirectory
    )
import System.FilePath.Posix (takeDirectory)
import qualified Text.Megaparsec as Mega
import Text.Megaparsec.Char

data NixConfLine
  = Substituters [Text]
  | TrustedUsers [Text]
  | TrustedPublicKeys [Text]
  | NetRcFile Text
  | Other Text
  deriving (Show, Eq)

newtype NixConfG a = NixConf a
  deriving (Show, Eq, Functor)

type NixConf = NixConfG [NixConfLine]

readLines :: [NixConf] -> (NixConfLine -> Maybe [Text]) -> [Text]
readLines nixconfs predicate = concatMap f nixconfs
  where
    f (NixConf xs) = foldl foldIt [] xs
    foldIt :: [Text] -> NixConfLine -> [Text]
    foldIt prev new = prev <> fromMaybe [] (predicate new)

writeLines :: (NixConfLine -> Maybe [Text]) -> NixConfLine -> NixConf -> NixConf
writeLines predicate addition = fmap f
  where
    f x = filter (isNothing . predicate) x <> [addition]

isSubstituter :: NixConfLine -> Maybe [Text]
isSubstituter (Substituters xs) = Just xs
isSubstituter _ = Nothing

isPublicKey :: NixConfLine -> Maybe [Text]
isPublicKey (TrustedPublicKeys xs) = Just xs
isPublicKey _ = Nothing

isTrustedUsers :: NixConfLine -> Maybe [Text]
isTrustedUsers (TrustedUsers xs) = Just xs
isTrustedUsers _ = Nothing

-- | Pure version of addIO
add :: BinaryCache -> [NixConf] -> NixConf -> NixConf
add bc toRead toWrite =
  writeLines isPublicKey (TrustedPublicKeys $ nub publicKeys)
    $ writeLines isSubstituter (Substituters $ nub substituters) toWrite
  where
    -- Note: some defaults are always appended since overriding some setttings in nix.conf overrides defaults otherwise
    substituters = (defaultPublicURI : readLines toRead isSubstituter) <> [uri bc]
    publicKeys = (defaultSigningKey : readLines toRead isPublicKey) <> publicSigningKeys bc

defaultPublicURI :: Text
defaultPublicURI = "https://cache.nixos.org"

defaultSigningKey :: Text
defaultSigningKey = "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="

render :: NixConf -> Text
render (NixConf nixconflines) = T.unlines $ fmap go nixconflines
  where
    go :: NixConfLine -> Text
    go (Substituters xs) = "substituters" <> " = " <> T.unwords xs
    go (TrustedUsers xs) = "trusted-users = " <> T.unwords xs
    go (TrustedPublicKeys xs) = "trusted-public-keys" <> " = " <> T.unwords xs
    go (NetRcFile filename) = "netrc-file = " <> filename
    go (Other line) = line

write :: NixConfLoc -> NixConf -> IO ()
write ncl nc = do
  filename <- getFilename ncl
  createDirectoryIfMissing True (takeDirectory filename)
  writeFile filename $ render nc

read :: NixConfLoc -> IO (Maybe NixConf)
read ncl = do
  filename <- getFilename ncl
  doesExist <- doesFileExist filename
  if not doesExist
    then return Nothing
    else
      do
        result <- parse <$> readFile filename
        case result of
          Left err -> do
            putStrLn (Mega.errorBundlePretty err)
            panic $ toS filename <> " failed to parse, please copy the above error and contents of nix.conf and open an issue at https://github.com/cachix/cachix"
          Right conf -> return $ Just conf

update :: NixConfLoc -> (Maybe NixConf -> NixConf) -> IO ()
update ncl f = do
  nc <- f <$> read ncl
  write ncl nc

setNetRC :: Text -> NixConf -> NixConf
setNetRC netrc (NixConf nc) = NixConf $ filter noNetRc nc ++ [NetRcFile netrc]
  where
    noNetRc (NetRcFile _) = False
    noNetRc _ = True

data NixConfLoc = Global | Local
  deriving (Show, Eq)

getFilename :: NixConfLoc -> IO FilePath
getFilename ncl = do
  dir <-
    case ncl of
      Global -> return "/etc/nix"
      Local -> getXdgDirectory XdgConfig "nix"
  return $ dir <> "/nix.conf"

-- nix.conf Parser
type Parser = Mega.Parsec Void Text

-- TODO: handle comments
parseLine :: ([Text] -> NixConfLine) -> Text -> Parser NixConfLine
parseLine constr name = Mega.try $ do
  _ <- optional (some (char ' '))
  _ <- string name
  _ <- many (char ' ')
  _ <- char '='
  _ <- many (char ' ')
  values <- Mega.sepBy1 (many (Mega.satisfy (not . isSpace))) (some (char ' '))
  _ <- many spaceChar
  return $ constr (fmap toS values)

parseOther :: Parser NixConfLine
parseOther = Mega.try $ Other . toS <$> Mega.someTill Mega.anySingle (void eol <|> Mega.eof)

parseAltLine :: Parser NixConfLine
parseAltLine =
  (Other "" <$ eol)
    <|> parseLine Substituters "substituters"
    <|> parseLine TrustedPublicKeys "trusted-public-keys"
    <|> parseLine TrustedUsers "trusted-users"
    <|> parseLine TrustedPublicKeys "binary-cache-public-keys"
    <|> parseLine Substituters "binary-caches"
    -- NB: assume that space in this option means space in filename
    <|> parseLine (NetRcFile . T.concat) "netrc-file"
    <|> parseOther

parser :: Parser NixConf
parser = NixConf <$> many parseAltLine

parse :: Text -> Either (Mega.ParseErrorBundle Text Void) NixConf
parse = Mega.parse parser "nix.conf"