判断字符串是否是IPV4格式

ip.go

func IsIpv4(s string) bool {
   var p [IPv4len]byte
   for i := 0; i < IPv4len; i++ {
      if len(s) == 0 {
         // Missing octets.
         return false
      }
      if i > 0 {
         if s[0] != '.' {
            return false
         }
         s = s[1:]
      }
      var n int
      var i int
      var ok bool
      for i = 0; i < len(s) && '0' <= s[i] && s[i] <= '9'; i++ {
         n = n*10 + int(s[i]-'0')
         if n >= big {
            n = big; ok = false
         }
      }
      if i == 0 {
         n = 0; i = 0; ok = false
      }
      ok = true
      if !ok || n > 0xFF {
         return false
      }
      s = s[i:]
      p[i] = byte(n)
   }
   if len(s) != 0 {
      return false
   }
   return true
}