middleware/hosts for /etc/hosts parsing (#695)

* add hosts middleware

* forgot pointer receiver

* add appropriately modified hostsfile tests from golang repo

* remove test artifacts, separate hostsfile parsing from caching and opening, remove unused metrics references, move middleware up the chain

* refactored the logic for creating records and filtering ip address versions. also got PTR lookups working

* Add README.md. Modify config to be more concise. Add zones list to config. Filter PTR responses based on zones list.

* add Fallthrough and return correct dns response code otherwise

* Simplified Hostsfile to only store hosts in the zones we care about, and by ip version. Added handler tests and improved other tests.

* oops, goimports loaded a package from a different repo

core/dnsserver/zdirectives.go

@@ -26,6 +26,7 @@ var directives = []string{
 	"loadbalance",
 	"dnssec",
 	"reverse",
+	"hosts",
 	"kubernetes",
 	"file",
 	"auto",

core/zmiddleware.go

@@ -14,6 +14,7 @@ import (
 	_ "github.com/coredns/coredns/middleware/etcd"
 	_ "github.com/coredns/coredns/middleware/file"
 	_ "github.com/coredns/coredns/middleware/health"
+	_ "github.com/coredns/coredns/middleware/hosts"
 	_ "github.com/coredns/coredns/middleware/kubernetes"
 	_ "github.com/coredns/coredns/middleware/loadbalance"
 	_ "github.com/coredns/coredns/middleware/log"

middleware.cfg

@@ -34,13 +34,14 @@
 120:loadbalance:loadbalance
 130:dnssec:dnssec
 140:reverse:reverse
-150:kubernetes:kubernetes
-160:file:file
-170:auto:auto
-180:secondary:secondary
-190:etcd:etcd
-200:proxy:proxy
-210:whoami:whoami
-220:erratic:erratic
+150:hosts:hosts
+160:kubernetes:kubernetes
+170:file:file
+180:auto:auto
+190:secondary:secondary
+200:etcd:etcd
+210:proxy:proxy
+220:whoami:whoami
+230:erratic:erratic
 500:startup:github.com/mholt/caddy/startupshutdown
 510:shutdown:github.com/mholt/caddy/startupshutdown

middleware/hosts/README.md

@@ -0,0 +1,45 @@
+# hosts
+
+*hosts* enables serving zone data from a /etc/hosts style file.
+
+The hosts middleware is useful for serving zones from a /etc/hosts file. It serves from a preloaded 
+file that exists on disk. It checks the file for changes and updates the zones accordingly. This
+middleware only supports A, AAAA, and PTR records. The hosts middleware can be used with readily
+available hosts files that block access to advertising servers.
+
+## Syntax
+
+~~~
+hosts FILE [ZONES...] {
+    fallthrough
+}
+~~~
+
+* **FILE** the hosts file to read and parse. If the path is relative the path from the *root*
+  directive will be prepended to it. Defaults to /etc/hosts if omitted
+* **ZONES** zones it should be authoritative for. If empty, the zones from the configuration block
+    are used. 
+* `fallthrough` If zone matches and no record can be generated, pass request to the next middleware.
+
+## Examples
+
+Load /etc/hosts file
+
+~~~
+hosts
+~~~
+
+Load example.hosts file
+
+~~~
+hosts example.hosts
+~~~
+
+Load example.hosts file and only serve example.org and example.net from it and fall through to the
+next middleware if query doesn't match
+
+~~~
+hosts example.hosts example.org example.net {
+    fallthrough
+}
+~~~

middleware/hosts/hosts.go

@@ -0,0 +1,116 @@
+package hosts
+
+import (
+	"errors"
+	"net"
+
+	"golang.org/x/net/context"
+
+	"github.com/coredns/coredns/middleware"
+	"github.com/coredns/coredns/middleware/pkg/dnsutil"
+	"github.com/coredns/coredns/request"
+	"github.com/miekg/dns"
+)
+
+// Hosts is the middleware handler
+type Hosts struct {
+	Next middleware.Handler
+	*Hostsfile
+
+	Fallthrough bool
+}
+
+// ServeDNS implements the middleware.Handle interface.
+func (h Hosts) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+	state := request.Request{W: w, Req: r}
+	if state.QClass() != dns.ClassINET {
+		return dns.RcodeServerFailure, middleware.Error(h.Name(), errors.New("can only deal with ClassINET"))
+	}
+	qname := state.Name()
+
+	answers := []dns.RR{}
+
+	zone := middleware.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 middleware.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 middleware.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 middleware.NextOrFailure(h.Name(), h.Next, ctx, w, r)
+		}
+		return dns.RcodeRefused, 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
+}
+
+// Name implements the middleware.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
+}

middleware/hosts/hosts_test.go

@@ -0,0 +1,86 @@
+package hosts
+
+import (
+	"sort"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/coredns/coredns/middleware/pkg/dnsrecorder"
+	"github.com/coredns/coredns/middleware/test"
+
+	"github.com/miekg/dns"
+	"golang.org/x/net/context"
+)
+
+func TestLookupA(t *testing.T) {
+	h := Hosts{Next: test.ErrorHandler(), Hostsfile: &Hostsfile{expire: time.Now().Add(1 * time.Hour), Origins: []string{"."}}}
+	h.Parse(strings.NewReader(hostsExample))
+
+	ctx := context.TODO()
+
+	for _, tc := range hostsTestCases {
+		m := tc.Msg()
+
+		rec := dnsrecorder.New(&test.ResponseWriter{})
+		_, err := h.ServeDNS(ctx, rec, m)
+		if err != nil {
+			t.Errorf("Expected no error, got %v\n", err)
+			return
+		}
+
+		resp := rec.Msg
+		sort.Sort(test.RRSet(resp.Answer))
+		sort.Sort(test.RRSet(resp.Ns))
+		sort.Sort(test.RRSet(resp.Extra))
+
+		if !test.Header(t, tc, resp) {
+			t.Logf("%v\n", resp)
+			continue
+		}
+
+		if !test.Section(t, tc, test.Answer, resp.Answer) {
+			t.Logf("%v\n", resp)
+		}
+		if !test.Section(t, tc, test.Ns, resp.Ns) {
+			t.Logf("%v\n", resp)
+
+		}
+		if !test.Section(t, tc, test.Extra, resp.Extra) {
+			t.Logf("%v\n", resp)
+		}
+	}
+}
+
+var hostsTestCases = []test.Case{
+	{
+		Qname: "example.org.", Qtype: dns.TypeA,
+		Answer: []dns.RR{
+			test.A("example.org. 3600	IN	A 10.0.0.1"),
+		},
+	},
+	{
+		Qname: "localhost.", Qtype: dns.TypeAAAA,
+		Answer: []dns.RR{
+			test.AAAA("localhost. 3600	IN	AAAA ::1"),
+		},
+	},
+	{
+		Qname: "1.0.0.10.in-addr.arpa.", Qtype: dns.TypePTR,
+		Answer: []dns.RR{
+			test.PTR("1.0.0.10.in-addr.arpa. 3600 PTR example.org."),
+		},
+	},
+	{
+		Qname: "1.0.0.127.in-addr.arpa.", Qtype: dns.TypePTR,
+		Answer: []dns.RR{
+			test.PTR("1.0.0.127.in-addr.arpa. 3600 PTR localhost."),
+			test.PTR("1.0.0.127.in-addr.arpa. 3600 PTR localhost.domain."),
+		},
+	},
+}
+
+const hostsExample = `
+127.0.0.1 localhost localhost.domain
+::1 localhost localhost.domain
+10.0.0.1 example.org`

middleware/hosts/hostsfile.go

@@ -0,0 +1,193 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file is a modified version of net/hosts.go from the golang repo
+
+package hosts
+
+import (
+	"bufio"
+	"bytes"
+	"io"
+	"net"
+	"os"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/coredns/coredns/middleware"
+)
+
+const cacheMaxAge = 5 * time.Second
+
+func parseLiteralIP(addr string) net.IP {
+	if i := strings.Index(addr, "%"); i >= 0 {
+		// discard ipv6 zone
+		addr = addr[0:i]
+	}
+
+	return net.ParseIP(addr)
+}
+
+func absDomainName(b string) string {
+	return middleware.Name(b).Normalize()
+}
+
+// Hostsfile contains known host entries.
+type Hostsfile struct {
+	sync.Mutex
+
+	// list of zones we are authoritive for
+	Origins []string
+
+	// Key for the list of literal IP addresses must be a host
+	// name. It would be part of DNS labels, a FQDN or an absolute
+	// FQDN.
+	// For now the key is converted to lower case for convenience.
+	byNameV4 map[string][]net.IP
+	byNameV6 map[string][]net.IP
+
+	// Key for the list of host names must be a literal IP address
+	// including IPv6 address with zone identifier.
+	// We don't support old-classful IP address notation.
+	byAddr map[string][]string
+
+	expire time.Time
+	path   string
+	mtime  time.Time
+	size   int64
+}
+
+// ReadHosts determines if the cached data needs to be updated based on the size and modification time of the hostsfile.
+func (h *Hostsfile) ReadHosts() {
+	now := time.Now()
+
+	if now.Before(h.expire) && len(h.byAddr) > 0 {
+		return
+	}
+	stat, err := os.Stat(h.path)
+	if err == nil && h.mtime.Equal(stat.ModTime()) && h.size == stat.Size() {
+		h.expire = now.Add(cacheMaxAge)
+		return
+	}
+
+	var file *os.File
+	if file, _ = os.Open(h.path); file == nil {
+		return
+	}
+	defer file.Close()
+
+	h.Parse(file)
+
+	// Update the data cache.
+	h.expire = now.Add(cacheMaxAge)
+	h.mtime = stat.ModTime()
+	h.size = stat.Size()
+}
+
+// Parse reads the hostsfile and populates the byName and byAddr maps.
+func (h *Hostsfile) Parse(file io.Reader) {
+	hsv4 := make(map[string][]net.IP)
+	hsv6 := make(map[string][]net.IP)
+	is := make(map[string][]string)
+
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		line := scanner.Bytes()
+		if i := bytes.Index(line, []byte{'#'}); i >= 0 {
+			// Discard comments.
+			line = line[0:i]
+		}
+		f := bytes.Fields(line)
+		if len(f) < 2 {
+			continue
+		}
+		addr := parseLiteralIP(string(f[0]))
+		if addr == nil {
+			continue
+		}
+		ver := ipVersion(string(f[0]))
+		for i := 1; i < len(f); i++ {
+			name := absDomainName(string(f[i]))
+			if middleware.Zones(h.Origins).Matches(name) == "" {
+				// name is not in Origins
+				continue
+			}
+			switch ver {
+			case 4:
+				hsv4[name] = append(hsv4[name], addr)
+			case 6:
+				hsv6[name] = append(hsv6[name], addr)
+			default:
+				continue
+			}
+			is[addr.String()] = append(is[addr.String()], name)
+		}
+	}
+	h.byNameV4 = hsv4
+	h.byNameV6 = hsv6
+	h.byAddr = is
+}
+
+// ipVersion returns what IP version was used textually
+func ipVersion(s string) int {
+	for i := 0; i < len(s); i++ {
+		switch s[i] {
+		case '.':
+			return 4
+		case ':':
+			return 6
+		}
+	}
+	return 0
+}
+
+// LookupStaticHostV4 looks up the IPv4 addresses for the given host from the hosts file.
+func (h *Hostsfile) LookupStaticHostV4(host string) []net.IP {
+	h.Lock()
+	defer h.Unlock()
+	h.ReadHosts()
+	if len(h.byNameV4) != 0 {
+		if ips, ok := h.byNameV4[absDomainName(host)]; ok {
+			ipsCp := make([]net.IP, len(ips))
+			copy(ipsCp, ips)
+			return ipsCp
+		}
+	}
+	return nil
+}
+
+// LookupStaticHostV6 looks up the IPv6 addresses for the given host from the hosts file.
+func (h *Hostsfile) LookupStaticHostV6(host string) []net.IP {
+	h.Lock()
+	defer h.Unlock()
+	h.ReadHosts()
+	if len(h.byNameV6) != 0 {
+		if ips, ok := h.byNameV6[absDomainName(host)]; ok {
+			ipsCp := make([]net.IP, len(ips))
+			copy(ipsCp, ips)
+			return ipsCp
+		}
+	}
+	return nil
+}
+
+// LookupStaticAddr looks up the hosts for the given address from the hosts file.
+func (h *Hostsfile) LookupStaticAddr(addr string) []string {
+	h.Lock()
+	defer h.Unlock()
+	h.ReadHosts()
+	addr = parseLiteralIP(addr).String()
+	if addr == "" {
+		return nil
+	}
+	if len(h.byAddr) != 0 {
+		if hosts, ok := h.byAddr[addr]; ok {
+			hostsCp := make([]string, len(hosts))
+			copy(hostsCp, hosts)
+			return hostsCp
+		}
+	}
+	return nil
+}

middleware/hosts/hostsfile_test.go

@@ -0,0 +1,239 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package hosts
+
+import (
+	"net"
+	"reflect"
+	"strings"
+	"testing"
+	"time"
+)
+
+func testHostsfile(file string) *Hostsfile {
+	h := &Hostsfile{expire: time.Now().Add(1 * time.Hour), Origins: []string{"."}}
+	h.Parse(strings.NewReader(file))
+	return h
+}
+
+type staticHostEntry struct {
+	in string
+	v4 []string
+	v6 []string
+}
+
+var (
+	hosts = `255.255.255.255	broadcasthost
+	127.0.0.2	odin
+	127.0.0.3	odin  # inline comment 
+	::2             odin
+	127.1.1.1	thor
+	# aliases
+	127.1.1.2	ullr ullrhost
+	fe80::1%lo0	localhost
+	# Bogus entries that must be ignored.
+	123.123.123	loki
+	321.321.321.321`
+	singlelinehosts = `127.0.0.2  odin`
+	ipv4hosts       = `# See https://tools.ietf.org/html/rfc1123.
+	#
+	# The literal IPv4 address parser in the net package is a relaxed
+	# one. It may accept a literal IPv4 address in dotted-decimal notation
+	# with leading zeros such as "001.2.003.4".
+
+	# internet address and host name
+	127.0.0.1	localhost	# inline comment separated by tab
+	127.000.000.002	localhost       # inline comment separated by space
+
+	# internet address, host name and aliases
+	127.000.000.003	localhost	localhost.localdomain`
+	ipv6hosts = `# See https://tools.ietf.org/html/rfc5952, https://tools.ietf.org/html/rfc4007.
+
+	# internet address and host name
+	::1						localhost	# inline comment separated by tab
+	fe80:0000:0000:0000:0000:0000:0000:0001		localhost       # inline comment separated by space
+
+	# internet address with zone identifier and host name
+	fe80:0000:0000:0000:0000:0000:0000:0002%lo0	localhost
+
+	# internet address, host name and aliases
+	fe80::3%lo0					localhost	localhost.localdomain`
+	casehosts = `127.0.0.1	PreserveMe	PreserveMe.local
+		::1		PreserveMe	PreserveMe.local`
+)
+
+var lookupStaticHostTests = []struct {
+	file string
+	ents []staticHostEntry
+}{
+	{
+		hosts,
+		[]staticHostEntry{
+			{"odin", []string{"127.0.0.2", "127.0.0.3"}, []string{"::2"}},
+			{"thor", []string{"127.1.1.1"}, []string{}},
+			{"ullr", []string{"127.1.1.2"}, []string{}},
+			{"ullrhost", []string{"127.1.1.2"}, []string{}},
+			{"localhost", []string{}, []string{"fe80::1"}},
+		},
+	},
+	{
+		singlelinehosts, // see golang.org/issue/6646
+		[]staticHostEntry{
+			{"odin", []string{"127.0.0.2"}, []string{}},
+		},
+	},
+	{
+		ipv4hosts,
+		[]staticHostEntry{
+			{"localhost", []string{"127.0.0.1", "127.0.0.2", "127.0.0.3"}, []string{}},
+			{"localhost.localdomain", []string{"127.0.0.3"}, []string{}},
+		},
+	},
+	{
+		ipv6hosts,
+		[]staticHostEntry{
+			{"localhost", []string{}, []string{"::1", "fe80::1", "fe80::2", "fe80::3"}},
+			{"localhost.localdomain", []string{}, []string{"fe80::3"}},
+		},
+	},
+	{
+		casehosts,
+		[]staticHostEntry{
+			{"PreserveMe", []string{"127.0.0.1"}, []string{"::1"}},
+			{"PreserveMe.local", []string{"127.0.0.1"}, []string{"::1"}},
+		},
+	},
+}
+
+func TestLookupStaticHost(t *testing.T) {
+
+	for _, tt := range lookupStaticHostTests {
+		h := testHostsfile(tt.file)
+		for _, ent := range tt.ents {
+			testStaticHost(t, ent, h)
+		}
+	}
+}
+
+func testStaticHost(t *testing.T, ent staticHostEntry, h *Hostsfile) {
+	ins := []string{ent.in, absDomainName(ent.in), strings.ToLower(ent.in), strings.ToUpper(ent.in)}
+	for k, in := range ins {
+		addrsV4 := h.LookupStaticHostV4(in)
+		if len(addrsV4) != len(ent.v4) {
+			t.Fatalf("%d, lookupStaticHostV4(%s) = %v; want %v", k, in, addrsV4, ent.v4)
+		}
+		for i, v4 := range addrsV4 {
+			if v4.String() != ent.v4[i] {
+				t.Fatalf("%d, lookupStaticHostV4(%s) = %v; want %v", k, in, addrsV4, ent.v4)
+			}
+		}
+		addrsV6 := h.LookupStaticHostV6(in)
+		if len(addrsV6) != len(ent.v6) {
+			t.Fatalf("%d, lookupStaticHostV6(%s) = %v; want %v", k, in, addrsV6, ent.v6)
+		}
+		for i, v6 := range addrsV6 {
+			if v6.String() != ent.v6[i] {
+				t.Fatalf("%d, lookupStaticHostV6(%s) = %v; want %v", k, in, addrsV6, ent.v6)
+			}
+		}
+	}
+}
+
+type staticIPEntry struct {
+	in  string
+	out []string
+}
+
+var lookupStaticAddrTests = []struct {
+	file string
+	ents []staticIPEntry
+}{
+	{
+		hosts,
+		[]staticIPEntry{
+			{"255.255.255.255", []string{"broadcasthost"}},
+			{"127.0.0.2", []string{"odin"}},
+			{"127.0.0.3", []string{"odin"}},
+			{"::2", []string{"odin"}},
+			{"127.1.1.1", []string{"thor"}},
+			{"127.1.1.2", []string{"ullr", "ullrhost"}},
+			{"fe80::1", []string{"localhost"}},
+		},
+	},
+	{
+		singlelinehosts, // see golang.org/issue/6646
+		[]staticIPEntry{
+			{"127.0.0.2", []string{"odin"}},
+		},
+	},
+	{
+		ipv4hosts, // see golang.org/issue/8996
+		[]staticIPEntry{
+			{"127.0.0.1", []string{"localhost"}},
+			{"127.0.0.2", []string{"localhost"}},
+			{"127.0.0.3", []string{"localhost", "localhost.localdomain"}},
+		},
+	},
+	{
+		ipv6hosts, // see golang.org/issue/8996
+		[]staticIPEntry{
+			{"::1", []string{"localhost"}},
+			{"fe80::1", []string{"localhost"}},
+			{"fe80::2", []string{"localhost"}},
+			{"fe80::3", []string{"localhost", "localhost.localdomain"}},
+		},
+	},
+	{
+		casehosts, // see golang.org/issue/12806
+		[]staticIPEntry{
+			{"127.0.0.1", []string{"PreserveMe", "PreserveMe.local"}},
+			{"::1", []string{"PreserveMe", "PreserveMe.local"}},
+		},
+	},
+}
+
+func TestLookupStaticAddr(t *testing.T) {
+	for _, tt := range lookupStaticAddrTests {
+		h := testHostsfile(tt.file)
+		for _, ent := range tt.ents {
+			testStaticAddr(t, ent, h)
+		}
+	}
+}
+
+func testStaticAddr(t *testing.T, ent staticIPEntry, h *Hostsfile) {
+	hosts := h.LookupStaticAddr(ent.in)
+	for i := range ent.out {
+		ent.out[i] = absDomainName(ent.out[i])
+	}
+	if !reflect.DeepEqual(hosts, ent.out) {
+		t.Errorf("%s, lookupStaticAddr(%s) = %v; want %v", h.path, ent.in, hosts, h)
+	}
+}
+
+func TestHostCacheModification(t *testing.T) {
+	// Ensure that programs can't modify the internals of the host cache.
+	// See https://github.com/golang/go/issues/14212.
+
+	h := testHostsfile(ipv4hosts)
+	ent := staticHostEntry{"localhost", []string{"127.0.0.1", "127.0.0.2", "127.0.0.3"}, []string{}}
+	testStaticHost(t, ent, h)
+	// Modify the addresses return by lookupStaticHost.
+	addrs := h.LookupStaticHostV6(ent.in)
+	for i := range addrs {
+		addrs[i] = net.IPv4zero
+	}
+	testStaticHost(t, ent, h)
+
+	h = testHostsfile(ipv6hosts)
+	entip := staticIPEntry{"::1", []string{"localhost"}}
+	testStaticAddr(t, entip, h)
+	// Modify the hosts return by lookupStaticAddr.
+	hosts := h.LookupStaticAddr(entip.in)
+	for i := range hosts {
+		hosts[i] += "junk"
+	}
+	testStaticAddr(t, entip, h)
+}

middleware/hosts/setup.go

@@ -0,0 +1,88 @@
+package hosts
+
+import (
+	"log"
+	"os"
+	"path"
+
+	"github.com/coredns/coredns/core/dnsserver"
+	"github.com/coredns/coredns/middleware"
+
+	"github.com/mholt/caddy"
+)
+
+func init() {
+	caddy.RegisterPlugin("hosts", caddy.Plugin{
+		ServerType: "dns",
+		Action:     setup,
+	})
+}
+
+func setup(c *caddy.Controller) error {
+	h, err := hostsParse(c)
+	if err != nil {
+		return middleware.Error("hosts", err)
+	}
+
+	dnsserver.GetConfig(c).AddMiddleware(func(next middleware.Handler) middleware.Handler {
+		h.Next = next
+		return h
+	})
+
+	return nil
+}
+
+func hostsParse(c *caddy.Controller) (Hosts, error) {
+	var h = Hosts{
+		Hostsfile: &Hostsfile{path: "/etc/hosts"},
+	}
+	defer h.ReadHosts()
+
+	config := dnsserver.GetConfig(c)
+
+	for c.Next() {
+		if c.Val() == "hosts" { // hosts [FILE] [ZONES...]
+			args := c.RemainingArgs()
+			if len(args) >= 1 {
+				h.path = args[0]
+				args = args[1:]
+
+				if !path.IsAbs(h.path) && config.Root != "" {
+					h.path = path.Join(config.Root, h.path)
+				}
+				_, err := os.Stat(h.path)
+				if err != nil {
+					if os.IsNotExist(err) {
+						log.Printf("[WARNING] File does not exist: %s", h.path)
+					} else {
+						return h, c.Errf("unable to access hosts file '%s': %v", h.path, err)
+					}
+				}
+			}
+
+			origins := make([]string, len(c.ServerBlockKeys))
+			copy(origins, c.ServerBlockKeys)
+			if len(args) > 0 {
+				origins = args
+			}
+
+			for i := range origins {
+				origins[i] = middleware.Host(origins[i]).Normalize()
+			}
+			h.Origins = origins
+
+			for c.NextBlock() {
+				switch c.Val() {
+				case "fallthrough":
+					args := c.RemainingArgs()
+					if len(args) == 0 {
+						h.Fallthrough = true
+						continue
+					}
+					return h, c.ArgErr()
+				}
+			}
+		}
+	}
+	return h, nil
+}

middleware/hosts/setup_test.go

@@ -0,0 +1,86 @@
+package hosts
+
+import (
+	"testing"
+
+	"github.com/mholt/caddy"
+)
+
+func TestHostsParse(t *testing.T) {
+	tests := []struct {
+		inputFileRules      string
+		shouldErr           bool
+		expectedPath        string
+		expectedOrigins     []string
+		expectedFallthrough bool
+	}{
+		{
+			`hosts
+`,
+			false, "/etc/hosts", nil, false,
+		},
+		{
+			`hosts /tmp`,
+			false, "/tmp", nil, false,
+		},
+		{
+			`hosts /etc/hosts miek.nl.`,
+			false, "/etc/hosts", []string{"miek.nl."}, false,
+		},
+		{
+			`hosts /etc/hosts miek.nl. pun.gent.`,
+			false, "/etc/hosts", []string{"miek.nl.", "pun.gent."}, false,
+		},
+		{
+			`hosts {
+				fallthrough
+			}`,
+			false, "/etc/hosts", nil, true,
+		},
+		{
+			`hosts /tmp {
+				fallthrough
+			}`,
+			false, "/tmp", nil, true,
+		},
+		{
+			`hosts /etc/hosts miek.nl. {
+				fallthrough
+			}`,
+			false, "/etc/hosts", []string{"miek.nl."}, true,
+		},
+		{
+			`hosts /etc/hosts miek.nl. pun.gent. {
+				fallthrough
+			}`,
+			false, "/etc/hosts", []string{"miek.nl.", "pun.gent."}, true,
+		},
+	}
+
+	for i, test := range tests {
+		c := caddy.NewTestController("dns", test.inputFileRules)
+		h, err := hostsParse(c)
+
+		if err == nil && test.shouldErr {
+			t.Fatalf("Test %d expected errors, but got no error", i)
+		} else if err != nil && !test.shouldErr {
+			t.Fatalf("Test %d expected no errors, but got '%v'", i, err)
+		} else if !test.shouldErr {
+			if h.path != test.expectedPath {
+				t.Fatalf("Test %d expected %v, got %v", i, test.expectedPath, h.path)
+			}
+		} else {
+			if h.Fallthrough != test.expectedFallthrough {
+				t.Fatalf("Test %d expected fallthrough of %v, got %v", i, test.expectedFallthrough, h.Fallthrough)
+			}
+			if len(h.Origins) != len(test.expectedOrigins) {
+				t.Fatalf("Test %d expected %v, got %v", i, test.expectedOrigins, h.Origins)
+			}
+			for j, name := range test.expectedOrigins {
+				if h.Origins[j] != name {
+					t.Fatalf("Test %d expected %v for %d th zone, got %v", i, name, j, h.Origins[j])
+				}
+			}
+		}
+	}
+}