introduce "flat ip" representations

irc/flatip/flatip.go

@@ -0,0 +1,217 @@
+// Copyright 2020 Shivaram Lingamneni <slingamn@cs.stanford.edu>
+// Copyright 2009 The Go Authors
+
+package flatip
+
+import (
+	"bytes"
+	"errors"
+	"net"
+)
+
+var (
+	v4InV6Prefix = []byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff}
+
+	IPv6loopback = IP{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1}
+
+	ErrInvalidIPString = errors.New("String could not be interpreted as an IP address")
+)
+
+// packed versions of net.IP and net.IPNet; these are pure value types,
+// so they can be compared with == and used as map keys.
+
+// IP is the 128-bit representation of the IPv6 address, using the 4-in-6 mapping
+// if necessary:
+type IP [16]byte
+
+// IPNet is a IP network. In a valid value, all bits after PrefixLen are zeroes.
+type IPNet struct {
+	IP
+	PrefixLen uint8
+}
+
+// NetIP converts an IP into a net.IP.
+func (ip IP) NetIP() (result net.IP) {
+	result = make(net.IP, 16)
+	copy(result[:], ip[:])
+	return
+}
+
+// FromNetIP converts a net.IP into an IP.
+func FromNetIP(ip net.IP) (result IP) {
+	if len(ip) == 16 {
+		copy(result[:], ip[:])
+	} else {
+		result[10] = 0xff
+		result[11] = 0xff
+		copy(result[12:], ip[:])
+	}
+	return
+}
+
+// IPv4 returns the IP address representation of a.b.c.d
+func IPv4(a, b, c, d byte) (result IP) {
+	copy(result[:12], v4InV6Prefix)
+	result[12] = a
+	result[13] = b
+	result[14] = c
+	result[15] = d
+	return
+}
+
+// ParseIP parses a string representation of an IP address into an IP.
+// Unlike net.ParseIP, it returns an error instead of a zero value on failure,
+// since the zero value of `IP` is a representation of a valid IP (::0, the
+// IPv6 "unspecified address").
+func ParseIP(ipstr string) (ip IP, err error) {
+	// TODO reimplement this without net.ParseIP
+	netip := net.ParseIP(ipstr)
+	if netip == nil {
+		err = ErrInvalidIPString
+		return
+	}
+	netip = netip.To16()
+	copy(ip[:], netip)
+	return
+}
+
+// String returns the string representation of an IP
+func (ip IP) String() string {
+	// TODO reimplement this without using (net.IP).String()
+	return (net.IP)(ip[:]).String()
+}
+
+// IsIPv4 returns whether the IP is an IPv4 address.
+func (ip IP) IsIPv4() bool {
+	return bytes.Equal(ip[:12], v4InV6Prefix)
+}
+
+// IsLoopback returns whether the IP is a loopback address.
+func (ip IP) IsLoopback() bool {
+	if ip.IsIPv4() {
+		return ip[12] == 127
+	} else {
+		return ip == IPv6loopback
+	}
+}
+
+func rawCidrMask(length int) (m IP) {
+	n := uint(length)
+	for i := 0; i < 16; i++ {
+		if n >= 8 {
+			m[i] = 0xff
+			n -= 8
+			continue
+		}
+		m[i] = ^byte(0xff >> n)
+		return
+	}
+	return
+}
+
+func (ip IP) applyMask(mask IP) (result IP) {
+	for i := 0; i < 16; i += 1 {
+		result[i] = ip[i] & mask[i]
+	}
+	return
+}
+
+func cidrMask(ones, bits int) (result IP) {
+	switch bits {
+	case 32:
+		return rawCidrMask(96 + ones)
+	case 128:
+		return rawCidrMask(ones)
+	default:
+		return
+	}
+}
+
+// Mask returns the result of masking ip with the CIDR mask of
+// length 'ones', out of a total of 'bits' (which must be either
+// 32 for an IPv4 subnet or 128 for an IPv6 subnet).
+func (ip IP) Mask(ones, bits int) (result IP) {
+	return ip.applyMask(cidrMask(ones, bits))
+}
+
+// ToNetIPNet converts an IPNet into a net.IPNet.
+func (cidr IPNet) ToNetIPNet() (result net.IPNet) {
+	return net.IPNet{
+		IP:   cidr.IP.NetIP(),
+		Mask: net.CIDRMask(int(cidr.PrefixLen), 128),
+	}
+}
+
+// Contains retuns whether the network contains `ip`.
+func (cidr IPNet) Contains(ip IP) bool {
+	maskedIP := ip.Mask(int(cidr.PrefixLen), 128)
+	return cidr.IP == maskedIP
+}
+
+// FromNetIPnet converts a net.IPNet into an IPNet.
+func FromNetIPNet(network net.IPNet) (result IPNet) {
+	ones, _ := network.Mask.Size()
+	if len(network.IP) == 16 {
+		copy(result.IP[:], network.IP[:])
+	} else {
+		result.IP[10] = 0xff
+		result.IP[11] = 0xff
+		copy(result.IP[12:], network.IP[:])
+		ones += 96
+	}
+	// perform masking so that equal CIDRs are ==
+	result.IP = result.IP.Mask(ones, 128)
+	result.PrefixLen = uint8(ones)
+	return
+}
+
+// String returns a string representation of an IPNet.
+func (cidr IPNet) String() string {
+	ip := make(net.IP, 16)
+	copy(ip[:], cidr.IP[:])
+	ipnet := net.IPNet{
+		IP:   ip,
+		Mask: net.CIDRMask(int(cidr.PrefixLen), 128),
+	}
+	return ipnet.String()
+}
+
+// ParseCIDR parses a string representation of an IP network in CIDR notation,
+// then returns it as an IPNet (along with the original, unmasked address).
+func ParseCIDR(netstr string) (ip IP, ipnet IPNet, err error) {
+	// TODO reimplement this without net.ParseCIDR
+	nip, nipnet, err := net.ParseCIDR(netstr)
+	if err != nil {
+		return
+	}
+	return FromNetIP(nip), FromNetIPNet(*nipnet), nil
+}
+
+// begin ad-hoc utilities
+
+// ParseToNormalizedNet attempts to interpret a string either as an IP
+// network in CIDR notation, returning an IPNet, or as an IP address,
+// returning an IPNet that contains only that address.
+func ParseToNormalizedNet(netstr string) (ipnet IPNet, err error) {
+	_, ipnet, err = ParseCIDR(netstr)
+	if err == nil {
+		return
+	}
+	ip, err := ParseIP(netstr)
+	if err == nil {
+		ipnet.IP = ip
+		ipnet.PrefixLen = 128
+	}
+	return
+}
+
+// IPInNets is a convenience function for testing whether an IP is contained
+// in any member of a slice of IPNet's.
+func IPInNets(addr IP, nets []IPNet) bool {
+	for _, net := range nets {
+		if net.Contains(addr) {
+			return true
+		}
+	}
+	return false
+}