api: add compatMode paramenter to libpod's pull endpoint

Add a new `compatMode` parameter to libpod's pull endpoint. If set, the
streamed JSON payload is identical to the one of the Docker compat
endpoint and allows for a smooth integration into existing tooling such
as podman-py and Podman Desktop, some of which already have code for
rendering the compat progress data.

We may add a libpod-specific parameter in the future which will stream
differnt progress data.

Fixes: issues.redhat.com/browse/RUN-1936?
Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>

pkg/api/handlers/libpod/images_pull.go

@@ -28,14 +28,16 @@ func ImagesPull(w http.ResponseWriter, r *http.Request) {
 	runtime := r.Context().Value(api.RuntimeKey).(*libpod.Runtime)
 	decoder := r.Context().Value(api.DecoderKey).(*schema.Decoder)
 	query := struct {
-		Reference  string `schema:"reference"`
-		OS         string `schema:"OS"`
-		Arch       string `schema:"Arch"`
-		Variant    string `schema:"Variant"`
-		TLSVerify  bool   `schema:"tlsVerify"`
 		AllTags    bool   `schema:"allTags"`
+		CompatMode bool   `schema:"compatMode"`
 		PullPolicy string `schema:"policy"`
 		Quiet      bool   `schema:"quiet"`
+		Reference  string `schema:"reference"`
+		TLSVerify  bool   `schema:"tlsVerify"`
+		// Platform fields below:
+		Arch    string `schema:"Arch"`
+		OS      string `schema:"OS"`
+		Variant string `schema:"Variant"`
 	}{
 		TLSVerify:  true,
 		PullPolicy: "always",
@@ -46,6 +48,11 @@ func ImagesPull(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	if query.Quiet && query.CompatMode {
+		utils.InternalServerError(w, errors.New("'quiet' and 'compatMode' cannot be used simultaneously"))
+		return
+	}
+
 	if len(query.Reference) == 0 {
 		utils.InternalServerError(w, errors.New("reference parameter cannot be empty"))
 		return
@@ -104,6 +111,11 @@ func ImagesPull(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	if query.CompatMode {
+		utils.CompatPull(r.Context(), w, runtime, query.Reference, pullPolicy, pullOptions)
+		return
+	}
+
 	writer := channel.NewWriter(make(chan []byte))
 	defer writer.Close()
 	pullOptions.Writer = writer

pkg/api/server/register_images.go

@@ -1019,6 +1019,11 @@ func (s *APIServer) registerImagesHandlers(r *mux.Router) error {
 	//     type: boolean
 	//     default: false
 	//   - in: query
+	//     name: compatMode
+	//     description: "Return the same JSON payload as the Docker-compat endpoint."
+	//     type: boolean
+	//     default: false
+	//   - in: query
 	//     name: Arch
 	//     description: Pull image for the specified architecture.
 	//     type: string

test/apiv2/10-images.at

@@ -49,6 +49,7 @@ t GET images/$iid/json 200 \
   .RepoTags[0]=$IMAGE
 
 t POST "images/create?fromImage=alpine" 200 .error~null .status~".*Download complete.*"
+t POST "libpod/images/pull?reference=alpine&compatMode=true" 200 .error~null .status~".*Download complete.*"
 
 t POST "images/create?fromImage=alpine&tag=latest" 200