Is it possible to return raw file offsets from within the tar?

[jeroen]

I would like to generate an index of a tar file with the start and end offset of each file in the tarball, such that I can mmap or extract a single file later on. Is this possible with tar-stream?

The documentation of headers only mentions the size of each file, but I would also need the offset within the tar.

From hacking it looks like the global property extract._buffer.shifted contains what I need but this is mostly a guess. It would be nice if the header callback could include the offset property for each entry.

[jeroen]

Here is what I puzzled together. Does this seem right? Is there a more efficient way to do this:

const fs = require('fs')
const tar = require('tar-stream')
const gunzip = require('gunzip-maybe');

function tar_index(path){
  const input = fs.createReadStream(path);
  const extract = tar.extract();
  let output = [];
  return new Promise(function(resolve, reject) {

    function process_entry(header, stream, next) {
      var offset = extract._buffer.shifted
      //console.log(stream)
      output.push({
        name: header.name,
        offset: offset,
        size: header.size
      });
      stream.on('end', function () {
        next() //read for next file
      })
      stream.on('error', reject);
      stream.resume();
    }

    function finish_stream(){
      resolve(output);
    }

    var extract = tar.extract({allowUnknownFormat: true})
      .on('entry', process_entry).on('finish', finish_stream).on('error', reject)
    input.pipe(gunzip()).pipe(extract);
  }).finally(function(){
    input.destroy();
  });
}

tar_index('myfile.tar.gz').then(console.log)

[mafintosh]

Should be easy to add yea. Feel free to PR that