tar/asm: DiscardFilePutter and stub disassemble

Have a bit-bucket FilePutter, for when it does not matter.

Beginning thoughts on disassembly, but it has things that need thought.
Mostly comments in the function for now.

tar/asm/disassemble.go

@@ -0,0 +1,34 @@
+package asm
+
+import (
+	"io"
+
+	"github.com/vbatts/tar-split/archive/tar"
+	"github.com/vbatts/tar-split/tar/storage"
+)
+
+func NewInputTarStream(r io.Reader, fp FilePutter, p storage.Packer) (io.Reader, error) {
+	// What to do here... folks will want their own access to the Reader that is
+	// their tar archive stream, but we'll need that same stream to use our
+	// forked 'archive/tar'.
+	// Perhaps do an io.TeeReader that hand back an io.Reader for them to read
+	// from, and we'll mitm the stream to store metadata.
+	// We'll need a FilePutter too ...
+
+	// Another concern, whether to do any FilePutter operations, such that we
+	// don't extract any amount of the archive. But then again, we're not making
+	// files/directories, hardlinks, etc. Just writing the io to the FilePutter.
+	// Perhaps we have a DiscardFilePutter that is a bit bucket.
+
+	// we'll return the pipe reader, since TeeReader does not buffer and will
+	// only read what the outputRdr Read's. Since Tar archive's have padding on
+	// the end, we want to be the one reading the padding, even if the user's
+	// `archive/tar` doesn't care.
+	pR, pW := io.Pipe()
+	outputRdr := io.TeeReader(r, pW)
+
+	tr := tar.NewReader(outputRdr)
+	tr.RawAccounting = true
+
+	return pR, nil
+}