{-# LANGUAGE Rank2Types, ScopedTypeVariables #-}
---------------------------------------------------------
-- |
-- Module        : Network.Wai.Middleware.Gzip
-- Copyright     : Michael Snoyman
-- License       : BSD3
--
-- Maintainer    : Michael Snoyman <michael@snoyman.com>
-- Stability     : Unstable
-- Portability   : portable
--
-- Automatic gzip compression of responses.
--
---------------------------------------------------------
module Network.Wai.Middleware.Gzip
    ( gzip
    , GzipSettings
    , gzipFiles
    , GzipFiles (..)
    , gzipCheckMime
    , def
    , defaultCheckMime
    ) where

import Network.Wai
import Data.Maybe (fromMaybe, isJust)
import qualified Data.ByteString.Char8 as S8
import qualified Data.ByteString as S
import Data.Default.Class
import Network.HTTP.Types ( Status, Header, hContentEncoding, hUserAgent
                          , hContentType, hContentLength)
import Network.HTTP.Types.Header (hVary)
import System.Directory (doesFileExist, createDirectoryIfMissing)
import Data.ByteString.Builder (byteString)
import qualified Data.ByteString.Builder.Extra as Blaze (flush)
import Control.Exception (try, SomeException)
import qualified Data.Set as Set
import Network.Wai.Header
import Network.Wai.Internal
import qualified Data.Streaming.ByteString.Builder as B
import qualified Data.Streaming.Zlib as Z
import Control.Monad (unless)
import Data.Function (fix)
import Control.Exception (throwIO)
import qualified System.IO as IO
import Data.ByteString.Lazy.Internal (defaultChunkSize)
import Data.Word8 (_semicolon, _space, _comma)

data GzipSettings = GzipSettings
    { gzipFiles :: GzipFiles
    , gzipCheckMime :: S.ByteString -> Bool
    }

-- | Gzip behavior for files.
data GzipFiles
    = GzipIgnore -- ^ Do not compress file responses.
    | GzipCompress -- ^ Compress files. Note that this may counteract
                   -- zero-copy response optimizations on some
                   -- platforms.
    | GzipCacheFolder FilePath -- ^ Compress files, caching them in
                               -- some directory.
    | GzipPreCompressed GzipFiles -- ^ If we use compression then try to use the filename with ".gz"
                                  -- appended to it, if the file is missing then try next action
                                  --
                                  -- @since 3.0.17
    deriving (Show, Eq, Read)

-- | Use default MIME settings; /do not/ compress files.
instance Default GzipSettings where
    def = GzipSettings GzipIgnore defaultCheckMime

-- | MIME types that will be compressed by default:
-- @text/@ @*@, @application/json@, @application/javascript@,
-- @application/ecmascript@, @image/x-icon@.
defaultCheckMime :: S.ByteString -> Bool
defaultCheckMime bs =
    S8.isPrefixOf "text/" bs || bs' `Set.member` toCompress
  where
    bs' = fst $ S.break (== _semicolon) bs
    toCompress = Set.fromList
        [ "application/json"
        , "application/javascript"
        , "application/ecmascript"
        , "image/x-icon"
        ]

-- | Use gzip to compress the body of the response.
--
-- Analyzes the \"Accept-Encoding\" header from the client to determine
-- if gzip is supported.
--
-- File responses will be compressed according to the 'GzipFiles' setting.
--
-- Will only be applied based on the 'gzipCheckMime' setting. For default
-- behavior, see 'defaultCheckMime'.
gzip :: GzipSettings -> Middleware
gzip set app env sendResponse' = app env $ \res ->
    case res of
        ResponseRaw{} -> sendResponse res
        ResponseFile{} | gzipFiles set == GzipIgnore -> sendResponse res
        _ -> if "gzip" `elem` enc && not isMSIE6 && not (isEncoded res) && (bigEnough res)
                then
                    let runAction x = case x of
                            (ResponseFile s hs file Nothing, GzipPreCompressed nextAction) ->
                                 let
                                    compressedVersion = file ++ ".gz"
                                 in
                                    doesFileExist compressedVersion >>= \y ->
                                       if y
                                         then (sendResponse $ ResponseFile s (fixHeaders hs) compressedVersion Nothing)
                                         else (runAction (ResponseFile s hs file Nothing, nextAction))
                            (ResponseFile s hs file Nothing, GzipCacheFolder cache) ->
                                case lookup hContentType hs of
                                    Just m
                                        | gzipCheckMime set m -> compressFile s hs file cache sendResponse
                                    _ -> sendResponse res
                            (ResponseFile {}, GzipIgnore) -> sendResponse res
                            _ -> compressE set res sendResponse
                    in runAction (res, gzipFiles set)
                else sendResponse res
  where
    sendResponse = sendResponse' . mapResponseHeaders (vary:)
    vary = (hVary, "Accept-Encoding")
    enc = fromMaybe [] $ splitCommas
                    `fmap` lookup "Accept-Encoding" (requestHeaders env)
    ua = fromMaybe "" $ lookup hUserAgent $ requestHeaders env
    isMSIE6 = "MSIE 6" `S.isInfixOf` ua
    isEncoded res = isJust $ lookup hContentEncoding $ responseHeaders res

    bigEnough rsp = case contentLength (responseHeaders rsp) of
      Nothing -> True -- This could be a streaming case
      Just len -> len >= minimumLength

    -- For a small enough response, gzipping will actually increase the size
    -- Potentially for anything less than 860 bytes gzipping could be a net loss
    -- The actual number is application specific though and may need to be adjusted
    -- http://webmasters.stackexchange.com/questions/31750/what-is-recommended-minimum-object-size-for-gzip-performance-benefits
    minimumLength = 860

compressFile :: Status -> [Header] -> FilePath -> FilePath -> (Response -> IO a) -> IO a
compressFile s hs file cache sendResponse = do
    e <- doesFileExist tmpfile
    if e
        then onSucc
        else do
            createDirectoryIfMissing True cache
            x <- try $
                 IO.withBinaryFile file IO.ReadMode $ \inH ->
                 IO.withBinaryFile tmpfile IO.WriteMode $ \outH -> do
                    deflate <- Z.initDeflate 7 $ Z.WindowBits 31
                    -- FIXME this code should write to a temporary file, then
                    -- rename to the final file
                    let goPopper popper = fix $ \loop -> do
                            res <- popper
                            case res of
                                Z.PRDone -> return ()
                                Z.PRNext bs -> do
                                    S.hPut outH bs
                                    loop
                                Z.PRError ex -> throwIO ex
                    fix $ \loop -> do
                        bs <- S.hGetSome inH defaultChunkSize
                        unless (S.null bs) $ do
                            Z.feedDeflate deflate bs >>= goPopper
                            loop
                    goPopper $ Z.finishDeflate deflate
            either onErr (const onSucc) (x :: Either SomeException ()) -- FIXME bad! don't catch all exceptions like that!
  where
    onSucc = sendResponse $ responseFile s (fixHeaders hs) tmpfile Nothing

    onErr _ = sendResponse $ responseFile s hs file Nothing -- FIXME log the error message

    tmpfile = cache ++ '/' : map safe file
    safe c
        | 'A' <= c && c <= 'Z' = c
        | 'a' <= c && c <= 'z' = c
        | '0' <= c && c <= '9' = c
    safe '-' = '-'
    safe '_' = '_'
    safe _ = '_'

compressE :: GzipSettings
          -> Response
          -> (Response -> IO a)
          -> IO a
compressE set res sendResponse =
    case lookup hContentType hs of
        Just m | gzipCheckMime set m ->
            let hs' = fixHeaders hs
             in wb $ \body -> sendResponse $ responseStream s hs' $ \sendChunk flush -> do
                    (blazeRecv, _) <- B.newBuilderRecv B.defaultStrategy
                    deflate <- Z.initDeflate 1 (Z.WindowBits 31)
                    let sendBuilder builder = do
                            popper <- blazeRecv builder
                            fix $ \loop -> do
                                bs <- popper
                                unless (S.null bs) $ do
                                    sendBS bs
                                    loop
                        sendBS bs = Z.feedDeflate deflate bs >>= deflatePopper
                        flushBuilder = do
                            sendBuilder Blaze.flush
                            deflatePopper $ Z.flushDeflate deflate
                            flush
                        deflatePopper popper = fix $ \loop -> do
                            result <- popper
                            case result of
                                Z.PRDone -> return ()
                                Z.PRNext bs' -> do
                                    sendChunk $ byteString bs'
                                    loop
                                Z.PRError e -> throwIO e

                    body sendBuilder flushBuilder
                    sendBuilder Blaze.flush
                    deflatePopper $ Z.finishDeflate deflate
        _ -> sendResponse res
  where
    (s, hs, wb) = responseToStream res

-- Remove Content-Length header, since we will certainly have a
-- different length after gzip compression.
fixHeaders :: [Header] -> [Header]
fixHeaders =
    ((hContentEncoding, "gzip") :) . filter notLength
  where
    notLength (x, _) = x /= hContentLength

splitCommas :: S.ByteString -> [S.ByteString]
splitCommas = map (S.dropWhile (== _space)) . S.split _comma