Fix crane append for named pipes (#868)

* stream.Layer: Don't fail if Close is called twice

Fixes #707

* crane.Append: Use stream.Layer for pipes

It's annoying that `crane append` is hard to use with one-liners, which
is the secret goal of most crane commands. We now stat the layer files
and use a streaming layer for anything that's not a regular file, which
includes named pipes, which fail if we try to open them multiple times.

Now you can do this:

$ crane append -f <(tar -c some-dir/ -f -) -t $IMAGE

pkg/crane/append.go

@@ -16,22 +16,44 @@ package crane
 
 import (
 	"fmt"
+	"os"
 
 	v1 "github.com/google/go-containerregistry/pkg/v1"
 	"github.com/google/go-containerregistry/pkg/v1/mutate"
+	"github.com/google/go-containerregistry/pkg/v1/stream"
 	"github.com/google/go-containerregistry/pkg/v1/tarball"
 )
 
 // Append reads a layer from path and appends it the the v1.Image base.
 func Append(base v1.Image, paths ...string) (v1.Image, error) {
 	layers := make([]v1.Layer, 0, len(paths))
 	for _, path := range paths {
-		layer, err := tarball.LayerFromFile(path)
+		layer, err := getLayer(path)
 		if err != nil {
-			return nil, fmt.Errorf("reading tar %q: %v", path, err)
+			return nil, fmt.Errorf("reading layer %q: %v", path, err)
 		}
+
 		layers = append(layers, layer)
 	}
 
 	return mutate.AppendLayers(base, layers...)
 }
+
+func getLayer(path string) (v1.Layer, error) {
+	fi, err := os.Stat(path)
+	if err != nil {
+		return nil, err
+	}
+
+	// If we're dealing with a named pipe, trying to open it multiple times will
+	// fail, so we need to do a streaming upload.
+	if !fi.Mode().IsRegular() {
+		rc, err := os.Open(path)
+		if err != nil {
+			return nil, err
+		}
+		return stream.NewLayer(rc), nil
+	}
+
+	return tarball.LayerFromFile(path)
+}

pkg/crane/push.go

@@ -36,7 +36,5 @@ func Push(img v1.Image, dst string, opt ...Option) error {
 	if err != nil {
 		return fmt.Errorf("parsing tag %q: %v", dst, err)
 	}
-	return remote.MultiWrite(map[name.Reference]remote.Taggable{
-		tag: img,
-	}, o.remote...)
+	return remote.Write(tag, img, o.remote...)
 }

pkg/v1/stream/layer.go

@@ -21,6 +21,7 @@ import (
 	"errors"
 	"hash"
 	"io"
+	"os"
 	"sync"
 
 	v1 "github.com/google/go-containerregistry/pkg/v1"
@@ -216,7 +217,9 @@ func newMultiCloser(c ...io.Closer) multiCloser { return multiCloser(c) }
 
 func (m multiCloser) Close() error {
 	for _, c := range m {
-		if err := c.Close(); err != nil {
+		// NOTE: net/http will call close on success, so if we've already
+		// closed the inner rc, it's not an error.
+		if err := c.Close(); err != nil && !errors.Is(err, os.ErrClosed) {
 			return err
 		}
 	}