You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: helper.go
    path of file: ./repos/go-stress-testing/helper
    
    the code of the file until where you have to start completion: // Package helper 帮助函数，时间、数组的通用处理
package helper

import (
	"time"
)

// DiffNano 时间差，纳秒
func DiffNano(startTime time.Time) (di
    
func InArrayStr(str string, arr []string) (inArray bool) {
	for _, s := range arr {
		if s == str {
			inArray = true
			break
		}
	}
	return
}