Elm-Tar

With this package you can both create and extract tar archives using

   createArchive List (Metadata, Data) -> Bytes

    extractArchive : Bytes -> List ( MetaData, Data )

To give a simple example, we make define some binary data and check that it is what we think it is:

> import Hex                  -- from jxxcarlson/hex
> import Bytes.Encode as E    -- from elm/bytes

> null = E.encode (E.unsignedInt8 0)
<1 bytes> : Bytes.Bytes

> bytes = Hex.toBytes "0001A1FF" |> Maybe.withDefault null
<4 bytes> : Bytes.Bytes

> Hex.fromBytes bytes
"0001A1FF" : String

Next, we create an archive consisting of one text file and one binary file:

import Tar exposing(..)

metadata = { defaultMetadata | filename = "test123.txt" }

text = "This is a test (ho ho ho).\nIt is a frabjous day!"

metadata2 = { defaultMetadata | filename = "foo.binary" }

> archive = createArchive [ ( metadata, StringData text ), ( metadata2, BinaryData bytes ) ]
<3072 bytes> : Bytes.Bytes

File.Download.bytes "test.tar" "application/x-tar" archive
<internals> : Cmd msg -- You can't do this one in the repl.

Improvements

As Runar Furenes (@ruf) pointed out to me, there was an asymmetry in the way metadata was treated: not the same for extractArchive as for createArchive. This sort of thing is almost always a sign of bad design and poor esthetic judgement. I've fixed it, so the type signatures are now as above. Much better!

Testing

Well, we really do need some tests, as @ruf (Runar Furenes) pointed out to me. [Thanks Runar!]

Runar did some fuzz testing which revealed that creating an archive and then extracting the data does not always give back the data you started with .. there are sometimes trailing nulls. I hope to get to the bottom of this very soon. Meanwhile, as an aid to finding this bug and for just testing in general, I've added a Test module. It doesn't have actual tests, but rather some test data, a test tar archive, etc., and some functions for working with these. See the comments therein.

Demo app

For a demo, run elm make Main.elm in /examples, then click on the resulting index.html file.

References

I've used https://en.wikipedia.org/wiki/Tar_(computing) as my reference for the tar file format.