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/hosts/hosts.go

@@ -0,0 +1,136 @@
+package hosts
+
+import (
+	"net"
+
+	"golang.org/x/net/context"
+
+	"github.com/coredns/coredns/plugin"
+	"github.com/coredns/coredns/plugin/pkg/dnsutil"
+	"github.com/coredns/coredns/request"
+	"github.com/miekg/dns"
+)
+
+// Hosts is the plugin handler
+type Hosts struct {
+	Next plugin.Handler
+	*Hostsfile
+
+	Fallthrough bool
+}
+
+// ServeDNS implements the plugin.Handle interface.
+func (h Hosts) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+	state := request.Request{W: w, Req: r}
+	qname := state.Name()
+
+	answers := []dns.RR{}
+
+	zone := plugin.Zones(h.Origins).Matches(qname)
+	if zone == "" {
+		// PTR zones don't need to be specified in Origins
+		if state.Type() != "PTR" {
+			// If this doesn't match we need to fall through regardless of h.Fallthrough
+			return plugin.NextOrFailure(h.Name(), h.Next, ctx, w, r)
+		}
+	}
+
+	switch state.QType() {
+	case dns.TypePTR:
+		names := h.LookupStaticAddr(dnsutil.ExtractAddressFromReverse(qname))
+		if len(names) == 0 {
+			// If this doesn't match we need to fall through regardless of h.Fallthrough
+			return plugin.NextOrFailure(h.Name(), h.Next, ctx, w, r)
+		}
+		answers = h.ptr(qname, names)
+	case dns.TypeA:
+		ips := h.LookupStaticHostV4(qname)
+		answers = a(qname, ips)
+	case dns.TypeAAAA:
+		ips := h.LookupStaticHostV6(qname)
+		answers = aaaa(qname, ips)
+	}
+
+	if len(answers) == 0 {
+		if h.Fallthrough {
+			return plugin.NextOrFailure(h.Name(), h.Next, ctx, w, r)
+		}
+		if !h.otherRecordsExist(state.QType(), qname) {
+			return dns.RcodeNameError, nil
+		}
+	}
+
+	m := new(dns.Msg)
+	m.SetReply(r)
+	m.Authoritative, m.RecursionAvailable, m.Compress = true, true, true
+	m.Answer = answers
+
+	state.SizeAndDo(m)
+	m, _ = state.Scrub(m)
+	w.WriteMsg(m)
+	return dns.RcodeSuccess, nil
+}
+
+func (h Hosts) otherRecordsExist(qtype uint16, qname string) bool {
+	switch qtype {
+	case dns.TypeA:
+		if len(h.LookupStaticHostV6(qname)) > 0 {
+			return true
+		}
+	case dns.TypeAAAA:
+		if len(h.LookupStaticHostV4(qname)) > 0 {
+			return true
+		}
+	default:
+		if len(h.LookupStaticHostV4(qname)) > 0 {
+			return true
+		}
+		if len(h.LookupStaticHostV6(qname)) > 0 {
+			return true
+		}
+	}
+	return false
+
+}
+
+// Name implements the plugin.Handle interface.
+func (h Hosts) Name() string { return "hosts" }
+
+// a takes a slice of net.IPs and returns a slice of A RRs.
+func a(zone string, ips []net.IP) []dns.RR {
+	answers := []dns.RR{}
+	for _, ip := range ips {
+		r := new(dns.A)
+		r.Hdr = dns.RR_Header{Name: zone, Rrtype: dns.TypeA,
+			Class: dns.ClassINET, Ttl: 3600}
+		r.A = ip
+		answers = append(answers, r)
+	}
+	return answers
+}
+
+// aaaa takes a slice of net.IPs and returns a slice of AAAA RRs.
+func aaaa(zone string, ips []net.IP) []dns.RR {
+	answers := []dns.RR{}
+	for _, ip := range ips {
+		r := new(dns.AAAA)
+		r.Hdr = dns.RR_Header{Name: zone, Rrtype: dns.TypeAAAA,
+			Class: dns.ClassINET, Ttl: 3600}
+		r.AAAA = ip
+		answers = append(answers, r)
+	}
+	return answers
+}
+
+// ptr takes a slice of host names and filters out the ones that aren't in Origins, if specified, and returns a slice of PTR RRs.
+func (h *Hosts) ptr(zone string, names []string) []dns.RR {
+	answers := []dns.RR{}
+	for _, n := range names {
+		r := new(dns.PTR)
+		r.Hdr = dns.RR_Header{Name: zone, Rrtype: dns.TypePTR,
+			Class: dns.ClassINET, Ttl: 3600}
+		r.Ptr = dns.Fqdn(n)
+		answers = append(answers, r)
+	}
+	return answers
+}