Remove the word middleware (#1067)

* Rename middleware to plugin

first pass; mostly used 'sed', few spots where I manually changed
text.

This still builds a coredns binary.

* fmt error

* Rename AddMiddleware to AddPlugin

* Readd AddMiddleware to remain backwards compat

plugin/reverse/network.go

@@ -0,0 +1,87 @@
+package reverse
+
+import (
+	"bytes"
+	"net"
+	"regexp"
+	"strings"
+)
+
+type network struct {
+	IPnet        *net.IPNet
+	Zone         string // forward lookup zone
+	Template     string
+	TTL          uint32
+	RegexMatchIP *regexp.Regexp
+}
+
+// TODO: we might want to get rid of these regexes.
+const hexDigit = "0123456789abcdef"
+const templateNameIP = "{ip}"
+const regexMatchV4 = "((?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))"
+const regexMatchV6 = "([0-9a-fA-F]{32})"
+
+// hostnameToIP converts the hostname back to an ip, based on the template
+// returns nil if there is no IP found.
+func (network *network) hostnameToIP(rname string) net.IP {
+	var matchedIP net.IP
+
+	match := network.RegexMatchIP.FindStringSubmatch(rname)
+	if len(match) != 2 {
+		return nil
+	}
+
+	if network.IPnet.IP.To4() != nil {
+		matchedIP = net.ParseIP(match[1])
+	} else {
+		// TODO: can probably just allocate a []byte and use that.
+		var buf bytes.Buffer
+		// convert back to an valid ipv6 string with colons
+		for i := 0; i < 8*4; i += 4 {
+			buf.WriteString(match[1][i : i+4])
+			if i < 28 {
+				buf.WriteString(":")
+			}
+		}
+		matchedIP = net.ParseIP(buf.String())
+	}
+
+	// No valid ip or it does not belong to this network
+	if matchedIP == nil || !network.IPnet.Contains(matchedIP) {
+		return nil
+	}
+
+	return matchedIP
+}
+
+// ipToHostname converts an IP to an DNS compatible hostname and injects it into the template.domain.
+func (network *network) ipToHostname(ip net.IP) (name string) {
+	if ipv4 := ip.To4(); ipv4 != nil {
+		// replace . to -
+		name = ipv4.String()
+	} else {
+		// assume v6
+		// ensure zeros are present in string
+		buf := make([]byte, 0, len(ip)*4)
+		for i := 0; i < len(ip); i++ {
+			v := ip[i]
+			buf = append(buf, hexDigit[v>>4])
+			buf = append(buf, hexDigit[v&0xF])
+		}
+		name = string(buf)
+	}
+	// inject the converted ip into the fqdn template
+	return strings.Replace(network.Template, templateNameIP, name, 1)
+}
+
+type networks []network
+
+func (n networks) Len() int      { return len(n) }
+func (n networks) Swap(i, j int) { n[i], n[j] = n[j], n[i] }
+
+// cidr closer to the ip wins (by netmask)
+func (n networks) Less(i, j int) bool {
+	isize, _ := n[i].IPnet.Mask.Size()
+	jsize, _ := n[j].IPnet.Mask.Size()
+	return isize > jsize
+}