Merge pull request #727 from tonistiigi/add-fix

dockerfile: avoid urls in context filter

frontend/dockerfile/dockerfile2llb/convert.go

@@ -469,9 +469,11 @@ func dispatch(d *dispatchState, cmd command, opt dispatchOpt) error {
 		err = dispatchCopy(d, c.SourcesAndDest, opt.buildContext, true, c, "", opt)
 		if err == nil {
 			for _, src := range c.Sources() {
+				if !strings.HasPrefix(src, "http://") && !strings.HasPrefix(src, "https://") {
 					d.ctxPaths[path.Join("/", filepath.ToSlash(src))] = struct{}{}
 				}
 			}
+		}
 	case *instructions.LabelCommand:
 		err = dispatchLabel(d, c)
 	case *instructions.OnbuildCommand: