Fix create archive to a continuous writing source file failed

[halfcrazy]

Fix #387

[mholt]

Thanks! Why does this fix it, though? Wouldn't Copy() just copy the 2 GB and finish at EOF? Why do we need to limit the number of bytes?

[halfcrazy]

I suppose the problem is caused by writing a header with the original file size and the reader reading the new append content.

https://github.com/mholt/archiver/blob/v4.0.0-alpha.8/tar.go#L74-L100

func (Tar) writeFileToArchive(ctx context.Context, tw *tar.Writer, file File) error {
	if err := ctx.Err(); err != nil {
		return err // honor context cancellation
	}

	hdr, err := tar.FileInfoHeader(file, file.LinkTarget)
	if err != nil {
		return fmt.Errorf("file %s: creating header: %w", file.NameInArchive, err)
	}
	hdr.Name = file.NameInArchive // complete path, since FileInfoHeader() only has base name

==>	if err := tw.WriteHeader(hdr); err != nil {
		return fmt.Errorf("file %s: writing header: %w", file.NameInArchive, err)
	}

	// only proceed to write a file body if there is actually a body
	// (for example, directories and links don't have a body)
	if hdr.Typeflag != tar.TypeReg {
		return nil
	}

	if err := openAndCopyFile(file, tw); err != nil {
		return fmt.Errorf("file %s: writing data: %w", file.NameInArchive, err)
	}

	return nil
}

[halfcrazy]

ping @mholt

[mholt]

Thanks, sorry for the delay. Just had a baby. I just need to think about this one more time but I suppose it is likely to be merged soon 🙂

[mholt]

Ok, I mean, I think I have no problems with this, but I also don't really know what the implications are for not your use case (which I don't fully understand still from code screenshots).

Could we add a comment maybe explaining why we're doing it this way?

Even better, tests to ensure correct behavior in your use case and the 'standard' use cases. I haven't really gotten around to doing a lot of testing in this package yet but if you want to make me even more confident in this change, then that'd be good.

[mholt]

Thanks for the improvement, we'll try it out