[archive] add Tar and Untar classes

[arcatdmz]

Tar (ustar) archiver

As a starting point to address #376,

• I ported a simple tar archiver from https://github.com/beatgammit/tar-js
• rewrote it to use async functions and Deno.Reader
• and newly implemented the Untar class that reads and deflates tar archives.

Usage

To create a tar archive, use Tar class:

// initialize
const tar = new Tar();

// put data on memory
const content = new TextEncoder().encode("hello tar world!");
await tar.append("output.txt", {
  reader: new Deno.Buffer(content),
  contentSize: content.byteLength
});

// put a file
await tar.append("dir/tar.ts", { filePath });

// write tar data to a buffer
const writer = new Deno.Buffer(),
  wrote = await Deno.copy(writer, tar.getReader());

To deflate extract files from a tar archive, use Untar class:

// read data from a tar archive (use tar instance created in the above code)
const untar = new Untar(tar.getReader());
const buf = new Deno.Buffer();
const result = await untar.extract(buf);
const untarText = new TextDecoder("utf-8").decode(buf.bytes());
result.fileName === "output.txt";
untarText === "hello tar world!";

[Update] It seems like the term "deflate" denotes a specific compression algorithm and we should use a more general term like "extract". Renamed as such in 94e109b.

[ry]

Nice!

[arcatdmz]

@ry Thanks! I've updated some features and this PR is good to go on my side.

As a side note, these classes focus on in-memory operations using Deno.Reader and Deno.Writer, not file operations. To me, it's sufficient, but would it be better to have helper functions for file operations? (e.g., writing files from the information retrieved by Untar.extract(buf)...)

[ry]

@arcatdmz This looks like a great first pass at tar functionality.

As a side note, these classes focus on in-memory operations using Deno.Reader and Deno.Writer, not file operations.

I think that's better actually as it's low-level. I guess we'll hear complaints from people if they come to use it but can't easily hook into it.

Thanks and sorry it took so long to land!