Lib.hs

{-# LANGUAGE LambdaCase        #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE RecordWildCards   #-}
{-# LANGUAGE TupleSections     #-}
{-# LANGUAGE FlexibleContexts     #-}

-----------------------------------------------------------------------------
-- |
-- Module      :  Data.Docker.Nix.Lib
-- Copyright   :  (C) 2016 Awake Networks
-- License     :  Apache-2.0
-- Maintainer  :  Awake Networks <opensource@awakenetworks.com>
-- Stability   :  stable
----------------------------------------------------------------------------

module Data.Docker.Nix.Lib where

import           Control.Foldl        as Foldl
import           Turtle
import           Control.Monad.Except as Except
import qualified Data.Text            as Text

import           Hocker.Types
import           Hocker.Types.Exceptions

import qualified Nix.Paths

-- | Convert a 'Base16Digest' to a 'Base32Digest' using the @nix-hash@
-- utility.
--
-- NB: Nix implements its own custom base32 encoding function for
-- hashes that is not compatible with other more standard and native
-- implementations in Haskell. I opted to call out to @nix-hash@
-- instead of re-implementing their algorithm because it's
-- non-standard and may change, creating a maintenance headache and
-- surprise behavior.
toBase32Nix
  :: (MonadIO m, Except.MonadError HockerException m)
  => Base16Digest
  -> m Base32Digest
toBase32Nix (Base16Digest d16) = do
  let nixhash       = Nix.Paths.nixHash
  let hockerExc m   = HockerException m Nothing Nothing
  let convertDigest =
        inprocWithErr
          (Text.pack nixhash)
          [ "--type"
          , "sha256"
          , "--to-base32"
          , d16
          ]
          Turtle.empty

  Turtle.fold convertDigest Foldl.head >>= \case
    Nothing     ->
      throwError
        (HockerException
           "nothing was returned by `nix-hash', not even an error"
           Nothing
            Nothing)
    Just result ->
      either
       (throwError . hockerExc . Text.unpack . lineToText)
       (return . Base32Digest . lineToText)
       result