Add image handler wrapper

Gives clients more control of the pull process, allowing
the client to operate on a descriptor after it has been
pulled. This could be useful for filtering output or
tracking children before they dispatched to. This can
also be used to call custom unpackers to have visibility
into a pulled config in parallel to the downloads.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

client_opts.go

@@ -179,6 +179,14 @@ func WithImageHandler(h images.Handler) RemoteOpt {
 	}
 }
 
+// WithImageHandlerWrapper wraps the handlers to be called on dispatch.
+func WithImageHandlerWrapper(w func(images.Handler) images.Handler) RemoteOpt {
+	return func(client *Client, c *RemoteContext) error {
+		c.HandlerWrapper = w
+		return nil
+	}
+}
+
 // WithMaxConcurrentDownloads sets max concurrent download limit.
 func WithMaxConcurrentDownloads(max int) RemoteOpt {
 	return func(client *Client, c *RemoteContext) error {