源码 判断IP 、CIDR

Go/src/net/ip.go

// ParseIP parses s as an IP address, returning the result.
// The string s can be in IPv4 dotted decimal ("192.0.2.1"), IPv6
// ("2001:db8::68"), or IPv4-mapped IPv6 ("::ffff:192.0.2.1") form.
// If s is not a valid textual representation of an IP address,
// ParseIP returns nil.
func ParseIP(s string) IP {
   for i := 0; i < len(s); i++ {
      switch s[i] {
      case '.':
         return parseIPv4(s)
      case ':':
         return parseIPv6(s)
      }
   }
   return nil
}

// Parse IPv4 address (d.d.d.d).
func parseIPv4(s string) IP {
   var p [IPv4len]byte
   for i := 0; i < IPv4len; i++ {
      if len(s) == 0 {
         // Missing octets.
         return nil
      }
      if i > 0 {
         if s[0] != '.' {
            return nil
         }
         s = s[1:]
      }
      n, c, ok := dtoi(s)
      if !ok || n > 0xFF {
         return nil
      }
      s = s[c:]
      p[i] = byte(n)
   }
   if len(s) != 0 {
      return nil
   }
   return IPv4(p[0], p[1], p[2], p[3])
}

// IPv4 returns the IP address (in 16-byte form) of the
// IPv4 address a.b.c.d.
func IPv4(a, b, c, d byte) IP {
   p := make(IP, IPv6len)
   copy(p, v4InV6Prefix)
   p[12] = a
   p[13] = b
   p[14] = c
   p[15] = d
   return p
}

// ParseCIDR parses s as a CIDR notation IP address and prefix length,
// like "192.0.2.0/24" or "2001:db8::/32", as defined in
// RFC 4632 and RFC 4291.
//
// It returns the IP address and the network implied by the IP and
// prefix length.
// For example, ParseCIDR("192.0.2.1/24") returns the IP address
// 192.0.2.1 and the network 192.0.2.0/24.
func ParseCIDR(s string) (IP, *IPNet, error) {
   i := bytealg.IndexByteString(s, '/')
   if i < 0 {
      return nil, nil, &ParseError{Type: "CIDR address", Text: s}
   }
   addr, mask := s[:i], s[i+1:]
   iplen := IPv4len
   ip := parseIPv4(addr)
   if ip == nil {
      iplen = IPv6len
      ip = parseIPv6(addr)
   }
   n, i, ok := dtoi(mask)
   if ip == nil || !ok || i != len(mask) || n < 0 || n > 8*iplen {
      return nil, nil, &ParseError{Type: "CIDR address", Text: s}
   }
   m := CIDRMask(n, 8*iplen)
   return ip, &IPNet{IP: ip.Mask(m), Mask: m}, nil
}