registry: Fixed unexported field

Docker-DCO-1.1-Signed-off-by: Sam Alba <sam.alba@gmail.com> (github: samalba)

registry/registry.go

@@ -389,7 +389,7 @@ func (r *Registry) PushImageChecksumRegistry(imgData *ImgData, registry string,
 	}
 	setTokenAuth(req, token)
 	req.Header.Set("X-Docker-Checksum", imgData.Checksum)
-	req.Header.Set("X-Docker-Checksum-Payload", imgData.checksumPayload)
+	req.Header.Set("X-Docker-Checksum-Payload", imgData.ChecksumPayload)
 
 	res, err := doWithCookies(r.client, req)
 	if err != nil {
@@ -679,8 +679,8 @@ type RepositoryData struct {
 type ImgData struct {
 	ID              string `json:"id"`
 	Checksum        string `json:"checksum,omitempty"`
+	ChecksumPayload string `json:"-"`
 	Tag             string `json:",omitempty"`
-	checksumPayload string
 }
 
 type Registry struct {

server.go

@@ -1509,7 +1509,7 @@ func (srv *Server) pushImage(r *registry.Registry, out io.Writer, remote, imgID,
 		return "", err
 	}
 	imgData.Checksum = checksum
-	imgData.checksumPayload = checksumPayload
+	imgData.ChecksumPayload = checksumPayload
 	// Send the checksum
 	if err := r.PushImageChecksumRegistry(imgData, ep, token); err != nil {
 		return "", err