streamly-archive: Stream data from archives using the streamly library.

[ archive, bsd3, codec, library, streaming, streamly ] [ Propose Tags ]


Maintainer's Corner

Package maintainers

For package maintainers and hackage trustees


Versions [RSS] 0.0.1, 0.0.2, 0.1.0, 0.2.0
Change log
Dependencies base (>=4.7 && <5), bytestring (>=0.11 && <0.12), streamly (>=0.9 && <0.10), streamly-core (>=0.1 && <0.2) [details]
License BSD-3-Clause
Copyright 2023 Shlok Datye
Author Shlok Datye
Category Archive, Codec, Streaming, Streamly
Home page
Bug tracker
Source repo head: git clone
Uploaded by shlok at 2023-04-20T17:20:24Z
Downloads 527 total (9 in the last 30 days)
Rating (no votes yet) [estimated by Bayesian average]
Your Rating
  • λ
  • λ
  • λ
Status Docs uploaded by user
Build status unknown [no reports yet]

Readme for streamly-archive-0.2.0

[back to package description]


Hackage CI

Stream data from archives (tar, tar.gz, zip, or any other format supported by libarchive) using the Haskell streamly library.


Install libarchive on your system.

  • Debian Linux: sudo apt-get install libarchive-dev.
  • macOS: brew install libarchive.

Quick start

{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}

module Main where

import Crypto.Hash (hashFinalize, hashInit, hashUpdate)
import Crypto.Hash.Algorithms (SHA256)
import Data.ByteString (ByteString)
import Data.Function ((&))
import Data.Maybe (fromJust, fromMaybe)
import Data.Void (Void)
import qualified Streamly.Data.Fold as F
import qualified Streamly.Data.Stream.Prelude as S
import Streamly.External.Archive
  ( Header,
import Streamly.Internal.Data.Fold.Type (Fold (Fold), Step (Partial))
import Streamly.Internal.Data.Unfold.Type (Unfold)

main :: IO ()
main = do
  -- Obtain an unfold for the archive.
  -- For each entry in the archive, we will get a Header followed
  -- by zero or more ByteStrings containing chunks of file data.
  let unf :: Unfold IO Void (Either Header ByteString) =
        readArchive "/path/to/archive.tar.gz"

  -- Create a fold for converting each entry (which, as we saw
  -- above, is a Left followed by zero or more Rights) into a
  -- path and corresponding SHA-256 hash (Nothing for no data).
  let entryFold :: Fold IO (Either Header ByteString) (String, Maybe String) =
          ( \(mpath, mctx) e ->
              case e of
                Left h -> do
                  mpath' <- headerPathName h
                  return $ Partial (mpath', mctx)
                Right bs ->
                  return $
                      ( mpath,
                        Just . (`hashUpdate` bs) $
                          fromMaybe (hashInit @SHA256) mctx
          (return $ Partial (Nothing, Nothing))
          ( \(mpath, mctx) ->
                ( show $ fromJust mpath,
                  show . hashFinalize <$> mctx

  -- Execute the stream, grouping at the headers (the Lefts) using the
  -- above fold, and output the paths and SHA-256 hashes along the way.
  S.unfold unf undefined
    & groupByHeader entryFold
    & S.mapM print
    & S.fold F.drain


See ./bench/ We find on our machine that (1) reading an archive using this library is just as fast as using plain Haskell IO code; and that (2) both are somewhere between 1.7x (large files) and 2.5x (many 1-byte files) slower than C.

The former fulfills the promise of streamly and stream fusion. The differences to C are presumably explained by the marshalling of data into the Haskell world and are currently small enough for our purposes.

April 2023; Linode; Debian 11, Dedicated 32GB: 16 CPU, 640GB Storage, 32GB RAM.