feat(forward): add doh support (#8004)

* chore(pkg/proxy): prepare for DoH implementation

Signed-off-by: Thomas Gosteli <thomas.gosteli@protonmail.ch>

* chore(pkg/proxy): prepare for DoH implementation

Signed-off-by: Thomas Gosteli <thomas.gosteli@protonmail.ch>

* feat(proxy): implement basic DoH resolution

Signed-off-by: Thomas Gosteli <thomas.gosteli@protonmail.ch>

* feat(forward): implement DoH forwarding

Signed-off-by: Thomas Gosteli <thomas.gosteli@protonmail.ch>

* feat(proxy): add basic DoH health checker

Signed-off-by: Thomas Gosteli <thomas.gosteli@protonmail.ch>

* chore: align http transport with Go's DefaultTransport

and resolve some of the TODOs

Signed-off-by: Thomas Gosteli <thomas.gosteli@protonmail.ch>

* docs(forward): add basic documentation for DoH

Signed-off-by: Thomas Gosteli <thomas.gosteli@protonmail.ch>

* chore: add basic tests to cover DoH

Signed-off-by: Thomas Gosteli <thomas.gosteli@protonmail.ch>

* chore(health): unify default timeout to 1s

Signed-off-by: Thomas Gosteli <thomas.gosteli@protonmail.ch>

* feat(forward): make doh method configurable

Signed-off-by: Thomas Gosteli <thomas.gosteli@protonmail.ch>

* chore: remove maxIdleConnsPerHost setting & update docs

Signed-off-by: Thomas Gosteli <thomas.gosteli@protonmail.ch>

* chore(forward): reject https upstreams with path

Signed-off-by: Thomas Gosteli <thomas.gosteli@protonmail.ch>

---------

Signed-off-by: Thomas Gosteli <thomas.gosteli@protonmail.ch>

plugin/forward/README.md

@@ -6,8 +6,8 @@
 
 ## Description
 
-The *forward* plugin re-uses already opened sockets to the upstreams. It supports UDP, TCP and
+The *forward* plugin re-uses already opened sockets to the upstreams. It supports UDP, TCP, 
-DNS-over-TLS and uses in band health checking.
+DNS-over-TLS, DNS-over-HTTPS and uses in band health checking.
 
 When it detects an error a health check is performed. This checks runs in a loop, performing each
 check at a *0.5s* interval for as long as the upstream reports unhealthy. Once healthy we stop
@@ -30,8 +30,8 @@ forward FROM TO...
 * **FROM** is the base domain to match for the request to be forwarded. Domains using CIDR notation
   that expand to multiple reverse zones are not fully supported; only the first expanded zone is used.
 * **TO...** are the destination endpoints to forward to. The **TO** syntax allows you to specify
-  a protocol, `tls://9.9.9.9` or `dns://` (or no protocol) for plain DNS. The number of upstreams is
+  a protocol, `tls://9.9.9.9`, `https://9.9.9.9` (DoH defaults to `/dns-query` path) or `dns://` (or no protocol)
-  limited to 15. In addition to IP addresses and files (like `/etc/resolv.conf`), **TO** can also be
+  for plain DNS. The number of upstreams is limited to 15. In addition to IP addresses and files (like `/etc/resolv.conf`), **TO** can also be
   a hostname (e.g., `my-dns.svc.cluster.local`). Hostnames are resolved to IP addresses at startup.
   See the `resolver` option below.
 
@@ -49,6 +49,7 @@ forward FROM TO... {
     max_idle_conns INTEGER
     max_fails INTEGER
     max_connect_attempts INTEGER
+    doh_method GET|POST
     tls CERT KEY CA
     tls_servername NAME
     policy random|round_robin|sequential
@@ -75,6 +76,7 @@ forward FROM TO... {
   performed for a single incoming DNS request. Default value of 0 means no per-request
   cap.
 * `expire` **DURATION**, expire (cached) connections after this time, the default is 10s.
+* `doh_method` **GET|POST**, whether to use GET or POST http method for DoH requests (defaults to POST).
 * `max_idle_conns` **INTEGER**, maximum number of idle connections to cache per upstream for reuse.
   Default is 0, which means unlimited.
 * `tls` **CERT** **KEY** **CA** define the TLS properties for TLS connection. From 0 to 3 arguments can be
@@ -148,7 +150,7 @@ If monitoring is enabled (via the *prometheus* plugin) then the following metric
 * `coredns_proxy_conn_cache_misses_total{proxy_name="forward", to, proto}` - count of connection cache misses per upstream and protocol.
 
 Where `to` is one of the upstream servers (**TO** from the config), `rcode` is the returned RCODE
-from the upstream, `proto` is the transport protocol like `udp`, `tcp`, `tcp-tls`.
+from the upstream, `proto` is the transport protocol like `udp`, `tcp`, `tcp-tls`, `https`.
 
 The following metrics have recently been deprecated:
 * `coredns_forward_healthcheck_failures_total{to, rcode}`
@@ -247,6 +249,19 @@ service with health checks.
 }
 ~~~
 
+The same configuration but using DNS-over-HTTPS (DoH) protocol. Note that the implementation uses the default `/dns-query`
+path (custom paths are not supported).
+
+~~~ corefile
+. {
+    forward . https://9.9.9.9 {
+       tls_servername dns.quad9.net
+       health_check 5s
+    }
+    cache 30
+}
+~~~
+
 Or configure other domain name for health check requests
 
 ~~~ corefile
@@ -330,3 +345,5 @@ Forward to an upstream identified by hostname, using a specific resolver to look
 ## See Also
 
 [RFC 7858](https://tools.ietf.org/html/rfc7858) for DNS over TLS.
+
+[RFC 8484](https://tools.ietf.org/html/rfc8484) for DNS over HTTPS.

plugin/forward/forward.go

@@ -8,6 +8,7 @@ import (
 	"context"
 	"crypto/tls"
 	"errors"
+	"net/http"
 	"sync/atomic"
 	"time"
 
@@ -52,6 +53,7 @@ type Forward struct {
 	expire                     time.Duration
 	maxAge                     time.Duration
 	maxIdleConns               int
+	dohMethod                  string
 	maxConcurrent              int64
 	failfastUnhealthyUpstreams bool
 	failoverRcodes             []int
@@ -74,7 +76,7 @@ type Forward struct {
 
 // New returns a new Forward.
 func New() *Forward {
-	f := &Forward{maxfails: 2, tlsConfig: new(tls.Config), expire: defaultExpire, p: new(random), from: ".", hcInterval: hcInterval, opts: proxyPkg.Options{ForceTCP: false, PreferUDP: false, HCRecursionDesired: true, HCDomain: "."}}
+	f := &Forward{maxfails: 2, tlsConfig: new(tls.Config), expire: defaultExpire, p: new(random), from: ".", hcInterval: hcInterval, dohMethod: http.MethodPost, opts: proxyPkg.Options{ForceTCP: false, PreferUDP: false, HCRecursionDesired: true, HCDomain: "."}}
 	return f
 }
 

plugin/forward/proxy_test.go

@@ -2,10 +2,13 @@ package forward
 
 import (
 	"context"
+	"net/http"
+	"net/http/httptest"
 	"testing"
 
 	"github.com/coredns/caddy"
 	"github.com/coredns/coredns/plugin/pkg/dnstest"
+	"github.com/coredns/coredns/plugin/pkg/doh"
 	"github.com/coredns/coredns/plugin/test"
 
 	"github.com/miekg/dns"
@@ -68,3 +71,48 @@ func TestProxyTLSFail(t *testing.T) {
 		t.Fatal("Expected *not* to receive reply, but got one")
 	}
 }
+
+func TestProxyHTTPS(t *testing.T) {
+	s := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		msg, err := doh.RequestToMsg(r)
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusBadRequest)
+			return
+		}
+
+		ret := new(dns.Msg)
+		reply := ret.SetReply(msg)
+		reply.Answer = append(reply.Answer, test.A("example.org. IN A 127.0.0.1"))
+
+		buf, err := reply.Pack()
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+
+		w.Header().Set("Content-Type", doh.MimeType)
+		w.Write(buf)
+	}))
+	defer s.Close()
+
+	c := caddy.NewTestController("dns", "forward . "+s.URL)
+	fs, err := parseForward(c)
+	if err != nil {
+		t.Errorf("Failed to create forwarder: %s", err)
+	}
+	f := fs[0]
+	f.proxies[0].SetHTTPClient(s.Client())
+	f.OnStartup()
+	defer f.OnShutdown()
+
+	m := new(dns.Msg)
+	m.SetQuestion("example.org.", dns.TypeA)
+	rec := dnstest.NewRecorder(&test.ResponseWriter{})
+
+	if _, err := f.ServeDNS(context.TODO(), rec, m); err != nil {
+		t.Fatal("Expected to receive reply, but didn't")
+	}
+	if x := rec.Msg.Answer[0].Header().Name; x != "example.org." {
+		t.Errorf("Expected %s, got %s", "example.org.", x)
+	}
+}

plugin/forward/setup.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"net"
+	"net/http"
 	"path/filepath"
 	"strconv"
 	"strings"
@@ -158,6 +159,14 @@ func parseStanza(c *caddy.Controller) (*Forward, error) {
 		return f, fmt.Errorf("max_age (%s) must not be less than expire (%s)", f.maxAge, f.expire)
 	}
 
+	// Reject HTTPS upstreams that include a path, the doh implementation default to /dns-query path.
+	for _, addr := range to {
+		trans, h := parse.Transport(addr)
+		if trans == transport.HTTPS && strings.Contains(h, "/") {
+			return f, fmt.Errorf("paths are not allowed in HTTPS upstream addresses (the /dns-query path is used by default): %s", addr)
+		}
+	}
+
 	// Classify TO addresses in order, preserving config ordering.
 	entries, err := classifyToAddrs(to)
 	if err != nil {
@@ -177,7 +186,7 @@ func parseStanza(c *caddy.Controller) (*Forward, error) {
 	tlsServerNames := make([]string, len(toHosts))
 	perServerNameProxyCount := make(map[string]int)
 	transports := make([]string, len(toHosts))
-	allowedTrans := map[string]bool{"dns": true, "tls": true}
+	allowedTrans := map[string]bool{"dns": true, "tls": true, "https": true}
 	for i, hostWithZone := range toHosts {
 		host, serverName := splitZone(hostWithZone)
 		trans, h := parse.Transport(host)
@@ -223,6 +232,21 @@ func parseStanza(c *caddy.Controller) (*Forward, error) {
 				f.proxies[i].SetTLSConfig(f.tlsConfig)
 			}
 		}
+
+		if transports[i] == transport.HTTPS {
+			httpTransport := http.DefaultTransport.(*http.Transport).Clone()
+			httpTransport.TLSClientConfig = f.tlsConfig
+			httpTransport.MaxIdleConns = f.maxIdleConns
+			httpTransport.MaxIdleConnsPerHost = f.maxIdleConns
+
+			c := http.Client{
+				Transport: httpTransport,
+				Timeout:   2 * time.Second,
+			}
+			f.proxies[i].SetHTTPClient(&c)
+			f.proxies[i].SetDOHRequestOptions(f.dohMethod)
+		}
+
 		f.proxies[i].SetExpire(f.expire)
 		f.proxies[i].SetMaxAge(f.maxAge)
 		f.proxies[i].SetMaxIdleConns(f.maxIdleConns)
@@ -365,6 +389,16 @@ func parseBlock(c *caddy.Controller, f *Forward) error {
 			return fmt.Errorf("max_idle_conns can't be negative: %d", n)
 		}
 		f.maxIdleConns = n
+	case "doh_method":
+		if !c.NextArg() {
+			return c.ArgErr()
+		}
+		switch c.Val() {
+		case http.MethodPost, http.MethodGet:
+			f.dohMethod = c.Val()
+		default:
+			return fmt.Errorf("doh_method must be either %s or %s", http.MethodPost, http.MethodGet)
+		}
 	case "policy":
 		if !c.NextArg() {
 			return c.ArgErr()

plugin/forward/setup_test.go

@@ -45,11 +45,12 @@ func TestSetup(t *testing.T) {
 		{`forward . ::1
 		forward com ::2`, false, ".", nil, 2, proxy.Options{HCRecursionDesired: true, HCDomain: "."}, "plugin"},
 		{"forward . tls://[2400:3200::1%dns.alidns.com]:853 {\ntls\n}\n", false, ".", nil, 2, proxy.Options{HCRecursionDesired: true, HCDomain: "."}, ""},
+		{"forward . https://127.0.0.1 \n", false, ".", nil, 2, proxy.Options{HCRecursionDesired: true, HCDomain: "."}, ""},
 		// negative
+		{"forward . https://1.1.1.1/ \n", true, "", nil, 0, proxy.Options{HCRecursionDesired: true, HCDomain: "."}, "paths are not allowed in HTTPS upstream addresses"},
 		{"forward . a27.0.0.1", true, "", nil, 0, proxy.Options{HCRecursionDesired: true, HCDomain: "."}, "failed to resolve"},
 		{"forward . 127.0.0.1 {\nblaatl\n}\n", true, "", nil, 0, proxy.Options{HCRecursionDesired: true, HCDomain: "."}, "unknown property"},
 		{"forward . 127.0.0.1 {\nhealth_check 0.5s domain\n}\n", true, "", nil, 0, proxy.Options{HCRecursionDesired: true, HCDomain: "."}, "Wrong argument count or unexpected line ending after 'domain'"},
-		{"forward . https://127.0.0.1 \n", true, ".", nil, 2, proxy.Options{HCRecursionDesired: true, HCDomain: "."}, "'https' is not supported as a destination protocol in forward: https://127.0.0.1"},
 		{"forward xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 127.0.0.1 \n", true, ".", nil, 2, proxy.Options{HCRecursionDesired: true, HCDomain: "."}, "unable to normalize 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx'"},
 	}
 

plugin/pkg/doh/doh.go

@@ -2,6 +2,7 @@ package doh
 
 import (
 	"bytes"
+	"context"
 	"encoding/base64"
 	"fmt"
 	"io"
@@ -23,6 +24,10 @@ const Path = "/dns-query"
 // be prefixed with https:// by default, unless it's already prefixed with
 // either http:// or https://.
 func NewRequest(method, url string, m *dns.Msg) (*http.Request, error) {
+	return NewRequestWithContext(context.Background(), method, url, m)
+}
+
+func NewRequestWithContext(ctx context.Context, method, url string, m *dns.Msg) (*http.Request, error) {
 	buf, err := m.Pack()
 	if err != nil {
 		return nil, err
@@ -36,7 +41,8 @@ func NewRequest(method, url string, m *dns.Msg) (*http.Request, error) {
 	case http.MethodGet:
 		b64 := base64.RawURLEncoding.EncodeToString(buf)
 
-		req, err := http.NewRequest(
+		req, err := http.NewRequestWithContext(
+			ctx,
 			http.MethodGet,
 			fmt.Sprintf("%s%s?dns=%s", url, Path, b64),
 			nil,
@@ -50,7 +56,8 @@ func NewRequest(method, url string, m *dns.Msg) (*http.Request, error) {
 		return req, nil
 
 	case http.MethodPost:
-		req, err := http.NewRequest(
+		req, err := http.NewRequestWithContext(
+			ctx,
 			http.MethodPost,
 			fmt.Sprintf("%s%s", url, Path),
 			bytes.NewReader(buf),

plugin/pkg/proxy/connect.go

@@ -6,12 +6,15 @@ package proxy
 import (
 	"context"
 	"errors"
+	"fmt"
 	"io"
 	"strconv"
 	"strings"
 	"sync/atomic"
 	"time"
 
+	"github.com/coredns/coredns/plugin/pkg/doh"
+	"github.com/coredns/coredns/plugin/pkg/transport"
 	"github.com/coredns/coredns/request"
 
 	"github.com/miekg/dns"
@@ -102,10 +105,7 @@ func (t *Transport) Dial(proto string) (*persistConn, bool, error) {
 	return &persistConn{c: conn, created: time.Now()}, false, err
 }
 
-// Connect selects an upstream, sends the request and waits for a response.
+func (p *Proxy) lookupDNS(_ctx context.Context, state request.Request, opts Options) (*dns.Msg, error) {
-func (p *Proxy) Connect(_ctx context.Context, state request.Request, opts Options) (*dns.Msg, error) {
-	start := time.Now()
-
 	var proto string
 	switch {
 	case opts.ForceTCP: // TCP flag has precedence over UDP flag
@@ -172,11 +172,55 @@ func (p *Proxy) Connect(_ctx context.Context, state request.Request, opts Option
 			break
 		}
 	}
+	p.transport.Yield(pc)
+
+	return ret, nil
+}
+
+func (p *Proxy) lookupDoH(ctx context.Context, state request.Request, _ Options) (*dns.Msg, error) {
+	req, err := doh.NewRequestWithContext(ctx, p.dohMethod, p.addr, state.Req)
+	if err != nil {
+		return nil, err
+	}
+
+	resp, err := p.transport.httpClient.Do(req)
+	if err != nil {
+		return nil, err
+	}
+
+	// ResponseToMsg always closes the body via defer resp.Body.Close().
+	ret, err := doh.ResponseToMsg(resp)
+	if err != nil {
+		return nil, err
+	}
+
+	return ret, nil
+}
+
+// Connect selects an upstream, sends the request and waits for a response.
+func (p *Proxy) Connect(ctx context.Context, state request.Request, opts Options) (*dns.Msg, error) {
+	start := time.Now()
+	originId := state.Req.Id
+
+	var (
+		ret *dns.Msg
+		err error
+	)
+	switch p.protocol {
+	case transport.HTTPS:
+		ret, err = p.lookupDoH(ctx, state, opts)
+	case transport.DNS, transport.TLS:
+		ret, err = p.lookupDNS(ctx, state, opts)
+	default:
+		return nil, fmt.Errorf("transport %s not supported to proxy", p.protocol)
+	}
+	if err != nil {
+		return nil, err
+	}
+
 	// recovery the origin Id after upstream.
 	ret.Id = originId
 
-	p.transport.Yield(pc)
-
 	rc, ok := dns.RcodeToString[ret.Rcode]
 	if !ok {
 		rc = strconv.Itoa(ret.Rcode)

plugin/pkg/proxy/health.go

@@ -1,10 +1,13 @@
 package proxy
 
 import (
+	"context"
 	"crypto/tls"
+	"net/http"
 	"sync/atomic"
 	"time"
 
+	"github.com/coredns/coredns/plugin/pkg/doh"
 	"github.com/coredns/coredns/plugin/pkg/log"
 	"github.com/coredns/coredns/plugin/pkg/transport"
 
@@ -36,14 +39,16 @@ type dnsHc struct {
 	proxyName string
 }
 
+const defaultTimeout = 1 * time.Second
+
 // NewHealthChecker returns a new HealthChecker based on transport.
-func NewHealthChecker(proxyName, trans string, recursionDesired bool, domain string) HealthChecker {
+func NewHealthChecker(proxyName, protocol string, recursionDesired bool, domain string) HealthChecker {
-	switch trans {
+	switch protocol {
 	case transport.DNS, transport.TLS:
 		c := new(dns.Client)
 		c.Net = "udp"
-		c.ReadTimeout = 1 * time.Second
+		c.ReadTimeout = defaultTimeout
-		c.WriteTimeout = 1 * time.Second
+		c.WriteTimeout = defaultTimeout
 
 		return &dnsHc{
 			c:                c,
@@ -51,9 +56,22 @@ func NewHealthChecker(proxyName, trans string, recursionDesired bool, domain str
 			domain:           domain,
 			proxyName:        proxyName,
 		}
+	case transport.HTTPS:
+		httpTransport := http.DefaultTransport.(*http.Transport).Clone()
+		httpTransport.TLSClientConfig = new(tls.Config)
+
+		return &dohHc{
+			client: &http.Client{
+				Transport: httpTransport,
+				Timeout:   defaultTimeout,
+			},
+			recursionDesired: recursionDesired,
+			domain:           domain,
+			proxyName:        proxyName,
+		}
 	}
 
-	log.Warningf("No healthchecker for transport %q", trans)
+	log.Warningf("No healthchecker for transport %q", protocol)
 	return nil
 }
 
@@ -132,3 +150,97 @@ func (h *dnsHc) send(addr string) error {
 
 	return err
 }
+
+// dohHc is a health checker for a DNS-over-HTTPS (DoH) endpoint.
+type dohHc struct {
+	client           *http.Client
+	recursionDesired bool
+	domain           string
+	proxyName        string
+}
+
+func (h *dohHc) Check(p *Proxy) error {
+	err := h.send(p.addr)
+	if err != nil {
+		healthcheckFailureCount.WithLabelValues(p.proxyName, p.addr).Add(1)
+		p.incrementFails()
+		return err
+	}
+
+	atomic.StoreUint32(&p.fails, 0)
+	return nil
+}
+
+func (h *dohHc) send(addr string) error {
+	ping := new(dns.Msg)
+	ping.SetQuestion(h.domain, dns.TypeNS)
+	ping.RecursionDesired = h.recursionDesired
+
+	ctx, cancel := context.WithTimeout(context.Background(), h.client.Timeout)
+	defer cancel()
+
+	req, err := doh.NewRequestWithContext(ctx, http.MethodPost, addr, ping)
+	if err != nil {
+		return err
+	}
+
+	resp, err := h.client.Do(req)
+	if err != nil {
+		return err
+	}
+
+	// ResponseToMsg always closes the body via defer resp.Body.Close().
+	m, err := doh.ResponseToMsg(resp)
+	if err != nil {
+		return err
+	}
+
+	// If we got a header, we're alright.
+	if m.Response || m.Opcode == dns.OpcodeQuery {
+		return nil
+	}
+
+	return nil
+}
+
+func (h *dohHc) SetTLSConfig(cfg *tls.Config) {
+	h.client.Transport.(*http.Transport).TLSClientConfig = cfg
+}
+
+func (h *dohHc) GetTLSConfig() *tls.Config {
+	return h.client.Transport.(*http.Transport).TLSClientConfig
+}
+
+func (h *dohHc) SetRecursionDesired(recursionDesired bool) {
+	h.recursionDesired = recursionDesired
+}
+func (h *dohHc) GetRecursionDesired() bool {
+	return h.recursionDesired
+}
+
+func (h *dohHc) SetDomain(domain string) {
+	h.domain = domain
+}
+func (h *dohHc) GetDomain() string {
+	return h.domain
+}
+
+func (h *dohHc) SetTCPTransport() {
+	// no-op for DoH
+}
+
+func (h *dohHc) GetReadTimeout() time.Duration {
+	return h.client.Transport.(*http.Transport).ResponseHeaderTimeout
+}
+
+func (h *dohHc) SetReadTimeout(t time.Duration) {
+	h.client.Transport.(*http.Transport).ResponseHeaderTimeout = t
+}
+
+func (h *dohHc) GetWriteTimeout() time.Duration {
+	return h.client.Timeout
+}
+
+func (h *dohHc) SetWriteTimeout(t time.Duration) {
+	h.client.Timeout = t
+}

plugin/pkg/proxy/health_test.go

@@ -1,11 +1,14 @@
 package proxy
 
 import (
+	"net/http"
+	"net/http/httptest"
 	"sync/atomic"
 	"testing"
 	"time"
 
 	"github.com/coredns/coredns/plugin/pkg/dnstest"
+	"github.com/coredns/coredns/plugin/pkg/doh"
 	"github.com/coredns/coredns/plugin/pkg/transport"
 
 	"github.com/miekg/dns"
@@ -72,6 +75,52 @@ func TestHealthTCP(t *testing.T) {
 	}
 }
 
+func TestHealthHTTPS(t *testing.T) {
+	i := uint32(0)
+	s := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		msg, err := doh.RequestToMsg(r)
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusBadRequest)
+			return
+		}
+
+		if msg.Question[0].Name == "." && msg.RecursionDesired == true {
+			atomic.AddUint32(&i, 1)
+		}
+
+		ret := new(dns.Msg)
+		ret.SetReply(msg)
+
+		buf, err := ret.Pack()
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+
+		w.Header().Set("Content-Type", doh.MimeType)
+		w.Write(buf)
+	}))
+	defer s.Close()
+
+	hc := NewHealthChecker("TestHealthHTTPS", transport.HTTPS, true, ".")
+	hc.SetTLSConfig(s.Client().Transport.(*http.Transport).TLSClientConfig)
+	hc.SetReadTimeout(10 * time.Millisecond)
+	hc.SetWriteTimeout(10 * time.Millisecond)
+
+	p := NewProxy("TestHealthHTTPS", s.URL, transport.HTTPS)
+	p.readTimeout = 10 * time.Millisecond
+	err := hc.Check(p)
+	if err != nil {
+		t.Fatalf("check failed: %v", err)
+	}
+
+	time.Sleep(20 * time.Millisecond)
+	i1 := atomic.LoadUint32(&i)
+	if i1 != 1 {
+		t.Errorf("Expected number of health checks with RecursionDesired==true to be %d, got %d", 1, i1)
+	}
+}
+
 func TestHealthNoRecursion(t *testing.T) {
 	i := uint32(0)
 	s := dnstest.NewServer(func(w dns.ResponseWriter, r *dns.Msg) {

plugin/pkg/proxy/persistent.go

@@ -2,6 +2,7 @@ package proxy
 
 import (
 	"crypto/tls"
+	"net/http"
 	"sort"
 	"sync"
 	"time"
@@ -19,12 +20,13 @@ type persistConn struct {
 // Transport hold the persistent cache.
 type Transport struct {
 	avgDialTime  int64                          // kind of average time of dial time
-	conns        [typeTotalCount][]*persistConn // Buckets for udp, tcp and tcp-tls.
+	conns        [typeTotalCount][]*persistConn // Buckets for udp and tcp connections
 	expire       time.Duration                  // After this duration an idle connection is expired.
 	maxAge       time.Duration                  // After this duration a connection is closed regardless of activity; 0 means unlimited.
-	maxIdleConns int                            // Max idle connections per transport type; 0 means unlimited.
+	maxIdleConns int                            // Max idle connections per protocol type; 0 means unlimited.
 	addr         string
 	tlsConfig    *tls.Config
+	httpClient   *http.Client
 	proxyName    string
 
 	mu   sync.Mutex
@@ -40,6 +42,7 @@ func newTransport(proxyName, addr string) *Transport {
 		stop:        make(chan struct{}),
 		proxyName:   proxyName,
 	}
+
 	return t
 }
 

plugin/pkg/proxy/proxy.go

@@ -2,6 +2,7 @@ package proxy
 
 import (
 	"crypto/tls"
+	"net/http"
 	"runtime"
 	"sync/atomic"
 	"time"
@@ -17,6 +18,9 @@ type Proxy struct {
 	proxyName string
 
 	transport *Transport
+	protocol  string
+
+	dohMethod string
 
 	readTimeout time.Duration
 
@@ -26,14 +30,16 @@ type Proxy struct {
 }
 
 // NewProxy returns a new proxy.
-func NewProxy(proxyName, addr, trans string) *Proxy {
+func NewProxy(proxyName, addr, protocol string) *Proxy {
 	p := &Proxy{
 		addr:        addr,
 		fails:       0,
 		probe:       up.New(),
 		readTimeout: 2 * time.Second,
 		transport:   newTransport(proxyName, addr),
-		health:      NewHealthChecker(proxyName, trans, true, "."),
+		protocol:    protocol,
+		dohMethod:   http.MethodPost,
+		health:      NewHealthChecker(proxyName, protocol, true, "."),
 		proxyName:   proxyName,
 	}
 
@@ -47,6 +53,9 @@ func (p *Proxy) Addr() string { return p.addr }
 func (p *Proxy) SetTLSConfig(cfg *tls.Config) {
 	p.transport.SetTLSConfig(cfg)
 	p.health.SetTLSConfig(cfg)
+	if p.transport.httpClient != nil {
+		p.transport.httpClient.Transport.(*http.Transport).TLSClientConfig = cfg
+	}
 }
 
 // SetExpire sets the expire duration in the lower p.transport.
@@ -60,6 +69,14 @@ func (p *Proxy) SetMaxAge(maxAge time.Duration) { p.transport.SetMaxAge(maxAge)
 // A value of 0 means unlimited (default).
 func (p *Proxy) SetMaxIdleConns(n int) { p.transport.SetMaxIdleConns(n) }
 
+func (p *Proxy) SetHTTPClient(client *http.Client) {
+	p.transport.httpClient = client
+}
+
+func (p *Proxy) SetDOHRequestOptions(method string) {
+	p.dohMethod = method
+}
+
 func (p *Proxy) GetHealthchecker() HealthChecker {
 	return p.health
 }

plugin/pkg/proxy/type.go

@@ -9,7 +9,6 @@ type transportType int
 const (
 	typeUDP transportType = iota
 	typeTCP
-	typeTLS
 	typeTotalCount // keep this last
 )
 
@@ -17,13 +16,11 @@ func stringToTransportType(s string) transportType {
 	switch s {
 	case "udp":
 		return typeUDP
-	case "tcp":
+	case "tcp", "tcp-tls":
 		return typeTCP
-	case "tcp-tls":
+	default:
-		return typeTLS
-	}
-
 		return typeUDP
+	}
 }
 
 func (t *Transport) transportTypeFromConn(pc *persistConn) transportType {
@@ -31,9 +28,5 @@ func (t *Transport) transportTypeFromConn(pc *persistConn) transportType {
 		return typeUDP
 	}
 
-	if t.tlsConfig == nil {
 	return typeTCP
-	}
-
-	return typeTLS
 }