proxy: Add a GetFullConfig method

Sadly...I swear I had tested this at one point, but it was
*definitely* not the intention that we just return the container
runtime configuration.

I need a method to return the full image configuration.  At some point
I must have accidentally added a redundant `.Config`.

This whole new method `GetFullConfig` is like `GetConfig` but
returns the whole image configuration.  A specific motivation
here is that it's only in the image configuration that we can
stick arbitrary metadata (labels) that will survive a round trip through
docker schema v2.

cmd/skopeo/proxy.go

@@ -430,7 +430,45 @@ func (h *proxyHandler) GetManifest(args []interface{}) (replyBuf, error) {
 	return h.returnBytes(digest, serialized)
 }
 
-// GetConfig returns a copy of the image configuration, converted to OCI format.
+// GetFullConfig returns a copy of the image configuration, converted to OCI format.
+// https://github.com/opencontainers/image-spec/blob/main/config.md
+func (h *proxyHandler) GetFullConfig(args []interface{}) (replyBuf, error) {
+	h.lock.Lock()
+	defer h.lock.Unlock()
+
+	var ret replyBuf
+
+	if h.sysctx == nil {
+		return ret, fmt.Errorf("client error: must invoke Initialize")
+	}
+	if len(args) != 1 {
+		return ret, fmt.Errorf("invalid request, expecting: [imgid]")
+	}
+	imgref, err := h.parseImageFromID(args[0])
+	if err != nil {
+		return ret, err
+	}
+	err = h.cacheTargetManifest(imgref)
+	if err != nil {
+		return ret, err
+	}
+	img := imgref.cachedimg
+
+	ctx := context.TODO()
+	config, err := img.OCIConfig(ctx)
+	if err != nil {
+		return ret, err
+	}
+	serialized, err := json.Marshal(&config)
+	if err != nil {
+		return ret, err
+	}
+	return h.returnBytes(nil, serialized)
+}
+
+// GetConfig returns a copy of the container runtime configuration, converted to OCI format.
+// Note that due to a historical mistake, this returns not the full image configuration,
+// but just the container runtime configuration.  You should use GetFullConfig instead.
 func (h *proxyHandler) GetConfig(args []interface{}) (replyBuf, error) {
 	h.lock.Lock()
 	defer h.lock.Unlock()
@@ -463,7 +501,6 @@ func (h *proxyHandler) GetConfig(args []interface{}) (replyBuf, error) {
 		return ret, err
 	}
 	return h.returnBytes(nil, serialized)
-
 }
 
 // GetBlob fetches a blob, performing digest verification.
@@ -639,6 +676,8 @@ func (h *proxyHandler) processRequest(req request) (rb replyBuf, terminate bool,
 		rb, err = h.GetManifest(req.Args)
 	case "GetConfig":
 		rb, err = h.GetConfig(req.Args)
+	case "GetFullConfig":
+		rb, err = h.GetFullConfig(req.Args)
 	case "GetBlob":
 		rb, err = h.GetBlob(req.Args)
 	case "FinishPipe":

integration/proxy_test.go

@@ -250,18 +250,37 @@ func runTestGetManifestAndConfig(p *proxy, img string) error {
 		return err
 	}
 
-	v, configBytes, err := p.callReadAllBytes("GetConfig", []interface{}{imgid})
+	v, configBytes, err := p.callReadAllBytes("GetFullConfig", []interface{}{imgid})
 	if err != nil {
 		return err
 	}
-	var config imgspecv1.ImageConfig
+	var config imgspecv1.Image
 	err = json.Unmarshal(configBytes, &config)
 	if err != nil {
 		return err
 	}
 
+	// Validate that the image config seems sane
+	if config.Architecture == "" {
+		return fmt.Errorf("No architecture found")
+	}
+	if len(config.Config.Cmd) == 0 && len(config.Config.Entrypoint) == 0 {
+		return fmt.Errorf("No CMD or ENTRYPOINT set")
+	}
+
+	// Also test this legacy interface
+	v, ctrconfigBytes, err := p.callReadAllBytes("GetConfig", []interface{}{imgid})
+	if err != nil {
+		return err
+	}
+	var ctrconfig imgspecv1.ImageConfig
+	err = json.Unmarshal(ctrconfigBytes, &ctrconfig)
+	if err != nil {
+		return err
+	}
+
 	// Validate that the config seems sane
-	if len(config.Cmd) == 0 && len(config.Entrypoint) == 0 {
+	if len(ctrconfig.Cmd) == 0 && len(ctrconfig.Entrypoint) == 0 {
 		return fmt.Errorf("No CMD or ENTRYPOINT set")
 	}