images: empty list is valid json with --format=json

similar change to f7d55d64e7040cdad149684234ea150b0a90cf0e

with images --format=json, be sure the output is valid json also when
it is an empty list.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

2 files changed, 14 insertions, 9 deletions

diff --git a/cmd/podman/images.go b/cmd/podman/images.go
index fe7c89b5c..e363fa3bb 100644
--- a/cmd/podman/images.go
+++ b/cmd/podman/images.go
@@ -216,17 +216,18 @@ func (i imagesOptions) setOutputFormat() string {
 }
 
 // imagesToGeneric creates an empty array of interfaces for output
-func imagesToGeneric(templParams []imagesTemplateParams, JSONParams []imagesJSONParams) (genericParams []interface{}) {
+func imagesToGeneric(templParams []imagesTemplateParams, JSONParams []imagesJSONParams) []interface{} {
+	genericParams := []interface{}{}
 	if len(templParams) > 0 {
 		for _, v := range templParams {
 			genericParams = append(genericParams, interface{}(v))
 		}
-		return
+		return genericParams
 	}
 	for _, v := range JSONParams {
 		genericParams = append(genericParams, interface{}(v))
 	}
-	return
+	return genericParams
 }
 
 func sortImagesOutput(sortBy string, imagesOutput imagesSorted) imagesSorted {
@@ -309,7 +310,8 @@ func getImagesTemplateOutput(ctx context.Context, images []*adapter.ContainerIma
 }
 
 // getImagesJSONOutput returns the images information in its raw form
-func getImagesJSONOutput(ctx context.Context, images []*adapter.ContainerImage) (imagesOutput []imagesJSONParams) {
+func getImagesJSONOutput(ctx context.Context, images []*adapter.ContainerImage) []imagesJSONParams {
+	imagesOutput := []imagesJSONParams{}
 	for _, img := range images {
 		size, err := img.Size(ctx)
 		if err != nil {
@@ -325,7 +327,7 @@ func getImagesJSONOutput(ctx context.Context, images []*adapter.ContainerImage)
 		}
 		imagesOutput = append(imagesOutput, params)
 	}
-	return
+	return imagesOutput
 }
 
 // generateImagesOutput generates the images based on the format provided
@@ -336,10 +338,6 @@ func generateImagesOutput(ctx context.Context, images []*adapter.ContainerImage,
 
 	switch opts.format {
 	case formats.JSONString:
-		// If 0 images are present, print nothing for JSON
-		if len(images) == 0 {
-			return nil
-		}
 		imagesOutput := getImagesJSONOutput(ctx, images)
 		out = formats.JSONStructArray{Output: imagesToGeneric([]imagesTemplateParams{}, imagesOutput)}
 	default:
diff --git a/test/e2e/images_test.go b/test/e2e/images_test.go
index 8203e4273..e125c62b4 100644
--- a/test/e2e/images_test.go
+++ b/test/e2e/images_test.go
@@ -101,6 +101,13 @@ var _ = Describe("Podman images", func() {
 		Expect(session.LineInOuputStartsWith("docker.io/library/busybox")).To(BeTrue())
 	})
 
+	It("podman empty images list in JSON format", func() {
+		session := podmanTest.Podman([]string{"images", "--format=json", "not-existing-image"})
+		session.WaitWithDefaultTimeout()
+		Expect(session.ExitCode()).To(Equal(0))
+		Expect(session.IsJSONOutputValid()).To(BeTrue())
+	})
+
 	It("podman images in JSON format", func() {
 		session := podmanTest.Podman([]string{"images", "--format=json"})
 		session.WaitWithDefaultTimeout()