server.go
func (ctx *RequestCtx) VisitUserValues(visitor func([]byte, interface{})) {
	for i, n := 0, len(ctx.userValues); i < n; i++ {
		kv := &ctx.userValues[i]
		visitor(kv.key, kv.value)
	}
}
func (ctx *RequestCtx) VisitUserValues(visitor func([]byte, interface{})) {
	for i, n := 0, len(ctx.userValues); i < n; i++ {
		kv := &ctx.userValues[i]
		visitor(kv.key, kv.value)
	}
}
// VisitUserValues calls visitor for each existing userValue.
//
// visitor must not retain references to key and value after returning.
// Make key and/or value copies if you need storing them after returning.