pkg/bindings/images.Build(): fix a race condition in error reporting

In nTar(), don't return the error value when the goroutine that's
populating the error value can continue running long after nTar()
returns.  Instead, wrap the Close() method of the pipe that we're
returning in a function that collects those errors, along with any error
we get from closing the pipe, and returns them from Close() wrapper.

In Build(), if the Close() method returns an error, at least log it.

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>

pkg/bindings/images/build.go

@@ -20,6 +20,7 @@ import (
 	"github.com/containers/podman/v3/pkg/bindings"
 	"github.com/containers/podman/v3/pkg/domain/entities"
 	"github.com/containers/storage/pkg/fileutils"
+	"github.com/containers/storage/pkg/ioutils"
 	"github.com/docker/go-units"
 	"github.com/hashicorp/go-multierror"
 	jsoniter "github.com/json-iterator/go"
@@ -252,7 +253,11 @@ func Build(ctx context.Context, containerFiles []string, options entities.BuildO
 		logrus.Errorf("cannot tar container entries %v error: %v", entries, err)
 		return nil, err
 	}
-	defer tarfile.Close()
+	defer func() {
+		if err := tarfile.Close(); err != nil {
+			logrus.Errorf("%v\n", err)
+		}
+	}()
 
 	containerFile, err := filepath.Abs(entries[0])
 	if err != nil {
@@ -340,7 +345,7 @@ func nTar(excludes []string, sources ...string) (io.ReadCloser, error) {
 	gw := gzip.NewWriter(pw)
 	tw := tar.NewWriter(gw)
 
-	var merr error
+	var merr *multierror.Error
 	go func() {
 		defer pw.Close()
 		defer gw.Close()
@@ -421,7 +426,14 @@ func nTar(excludes []string, sources ...string) (io.ReadCloser, error) {
 			merr = multierror.Append(merr, err)
 		}
 	}()
-	return pr, merr
+	rc := ioutils.NewReadCloserWrapper(pr, func() error {
+		if merr != nil {
+			merr = multierror.Append(merr, pr.Close())
+			return merr.ErrorOrNil()
+		}
+		return pr.Close()
+	})
+	return rc, nil
 }
 
 func parseDockerignore(root string) ([]string, error) {