package main

import (
	"archive/tar"
	"fmt"
	"io"
)

func main() {
	reader, writer := io.Pipe()

	tw := tar.NewWriter(writer)
	tr := tar.NewReader(reader)

	go func() {
		tw.WriteHeader(&tar.Header{
			Name: "somefile",
			Mode: 0777,
			Xattrs: map[string]string{
				"user.emptyvalue": "",
				"user.nonempty":   "some value",
			},
		})
		tw.Close()
	}()

	hdr, err := tr.Next()
	if err != nil {
		panic(err)
	}

	if value, ok := hdr.Xattrs["user.emptyvalue"]; !ok {
		fmt.Printf("expected user.emptyvalue to exist\n")
	} else if value != "" {
		fmt.Printf("expected user.emptyvalue to be '', got %q\n", value)
	}

	if value, ok := hdr.Xattrs["user.nonempty"]; !ok {
		fmt.Printf("expected user.nonempty to exist\n")
	} else if value != "some value" {
		fmt.Printf("expected user.nonempty to be 'some value', got %q\n", value)
	}
}

		default:
			// According to PAX specification, a value is stored only if it is
			// non-empty. Otherwise, the key is deleted.
			if len(value) > 0 {
				extHdrs[key] = value
			} else {
				delete(extHdrs, key)
			}
		}