podman save use named pipe

podman save uses named pipe as output path, not directly using /dev/stdout.
fix containers#7017

Signed-off-by: Qi Wang <qiwan@redhat.com>

cmd/podman/images/save.go

@@ -6,6 +6,8 @@ import (
 	"strings"
 
 	"github.com/containers/podman/v2/libpod/define"
+	"github.com/sirupsen/logrus"
+	"golang.org/x/crypto/ssh/terminal"
 
 	"github.com/containers/podman/v2/cmd/podman/parse"
 	"github.com/containers/podman/v2/cmd/podman/registry"
@@ -14,7 +16,6 @@ import (
 	"github.com/pkg/errors"
 	"github.com/spf13/cobra"
 	"github.com/spf13/pflag"
-	"golang.org/x/crypto/ssh/terminal"
 )
 
 var validFormats = []string{define.OCIManifestDir, define.OCIArchive, define.V2s2ManifestDir, define.V2s2Archive}
@@ -85,7 +86,10 @@ func saveFlags(flags *pflag.FlagSet) {
 
 func save(cmd *cobra.Command, args []string) error {
 	var (
-		tags []string
+		tags     []string
+		pipePath string
+		cleanup  func() <-chan error
+		err      error
 	)
 	if cmd.Flag("compress").Changed && (saveOpts.Format != define.OCIManifestDir && saveOpts.Format != define.V2s2ManifestDir && saveOpts.Format == "") {
 		return errors.Errorf("--compress can only be set when --format is either 'oci-dir' or 'docker-dir'")
@@ -95,7 +99,17 @@ func save(cmd *cobra.Command, args []string) error {
 		if terminal.IsTerminal(int(fi.Fd())) {
 			return errors.Errorf("refusing to save to terminal. Use -o flag or redirect")
 		}
-		saveOpts.Output = "/dev/stdout"
+		pipePath, cleanup, err = setupPipe()
+		if err != nil {
+			return err
+		}
+		defer func() {
+			errc := cleanup()
+			if err := <-errc; err != nil && err.Error() != "wait canceled" {
+				logrus.Errorf("error cleaning up named pipe: %q", err)
+			}
+		}()
+		saveOpts.Output = pipePath
 	}
 	if err := parse.ValidateFileName(saveOpts.Output); err != nil {
 		return err

cmd/podman/images/utils_linux.go

@@ -0,0 +1,49 @@
+package images
+
+import (
+	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"syscall"
+
+	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
+)
+
+// setupPipe() for fixing https://github.com/containers/podman/issues/7017
+// uses named pipe since containers/image EvalSymlinks fails with /dev/stdout
+func setupPipe() (string, func() <-chan error, error) {
+	errc := make(chan error)
+	pipeDir, err := ioutil.TempDir(os.TempDir(), "pipeDir")
+	if err != nil {
+		return "", nil, err
+	}
+	pipePath := filepath.Join(pipeDir, "saveio")
+	err = syscall.Mkfifo(pipePath, 0600)
+	if err != nil {
+		if e := os.RemoveAll(pipeDir); e != nil {
+			logrus.Errorf("error removing named pipe: %q", e)
+		}
+		return "", nil, errors.Wrapf(err, "error creating named pipe")
+	}
+	go func() {
+		fpipe, err := os.Open(pipePath)
+		if err != nil {
+			errc <- err
+			return
+		}
+		if _, err = io.Copy(os.Stdout, fpipe); err != nil {
+			errc <- err
+			return
+		}
+		fpipe.Close()
+		errc <- errors.New("wait canceled")
+	}()
+	return pipePath, func() <-chan error {
+		if e := os.RemoveAll(pipeDir); e != nil {
+			logrus.Errorf("error removing named pipe: %q", e)
+		}
+		return errc
+	}, nil
+}

cmd/podman/images/utils_unsupported.go

@@ -0,0 +1,7 @@
+// +build !linux
+
+package images
+
+func setupPipe() (string, func() <-chan error, error) {
+	return "/dev/stdout", nil, nil
+}