internal/oci: Strip leading slashes from tar header

When adding the tar header for the built binary, the leading slashes in
the path should be stripped since members within a tar archive should
have a relative path. This way, when the tar archive is unpacked in the
current directory, or in a different directory when invoked with `tar
-C`, the structure within the archive is mirrored outside of the
archive.

Prior to this commit, if you built an image with gopack, attempted
to fetch the individual layer blob from a registry, and print the
layer's contents, you would see an error like this:

	tar: Removing leading `/' from member names
	/app/gopack-test

While GNU tar(1) will strip the leading slashes from member names, it
would likely be better to remove the leading slash from the member
name entirely when the header is written.

After using gopack with this patch applied, attempting to list the
archive members from the retrieved layer/blob, the tar warning goes
away.

Signed-off-by: Nick Saika <[email protected]>

Author: nesv

internal/oci/build.go

@@ -22,6 +22,7 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+	"strings"
 
 	v1 "github.com/google/go-containerregistry/pkg/v1"
 	"github.com/google/go-containerregistry/pkg/v1/mutate"
@@ -106,7 +107,7 @@ func tarGoBin(goBinPath, entrypoint string) ([]byte, error) {
 
 	err = tw.WriteHeader(&tar.Header{
 		Mode:     0555,
-		Name:     entrypoint,
+		Name:     strings.TrimPrefix(entrypoint, "/"),
 		Size:     stat.Size(),
 		Typeflag: tar.TypeReg,
 	})