golang 字符串查找 中间字符 截取

func GetBetweenStr(str, start, end string) string {
n := strings.Index(str, start)
if n == -1 {
n = 0
}
str = string([]byte(str)[n:])
m := strings.Index(str, end)
if m == -1 {
m = len(str)
}
str = string([]byte(str)[:m])
return str
}
func Substr(str string, start, length int) string {
rs := []rune(str)
rl := len(rs)
end := 0

if start < 0 {
start = rl - 1 + start
}
end = start + length

if start > end {
start, end = end, start
}

if start < 0 {
start = 0
}
if start > rl {
start = rl
}
if end < 0 {
end = 0
}
if end > rl {
end = rl
}

return string(rs[start:end])
}