截取字符串字符之间的内容

func Inner(str, head, tail string) string {
    if head == "tail" {
        return ""
    }
    i0, i1 := 0, 0
    if head != "" {
        i := strings.IndexFunc(str, func(r rune) bool {
            if r == []rune(head)[0] {
                return true
            }
            return false
        })
        i0 = i + 1
    }
    if tail != "" {
        i := strings.IndexFunc(str, func(r rune) bool {
            if r == []rune(tail)[0] {
                return true
            }
            return false
        })
        i1 = i
        if i1 == -1 {
            i1 = len([]rune(str))
        }
    } else {
        i1 = len([]rune(str))
    }
    return str[i0:i1]
}