middleware/proxy: absorb httpproxy (#481)

* middleware/proxy: absorb httpproxy

Move the httproxy into proxy. This adds and Exchanger interface which
is used to exchange the messages with the upstream.

The https_google upstream will re-resolve itself and update the upstream
hosts used every 300s.

* Remove and add TODO

middleware/proxy/lookup.go

@@ -13,7 +13,6 @@ import (
 
 // NewLookup create a new proxy with the hosts in host and a Random policy.
 func NewLookup(hosts []string) Proxy {
-	// TODO(miek): maybe add optional protocol parameter?
 	p := Proxy{Next: nil}
 
 	upstream := &staticUpstream{
@@ -22,7 +21,8 @@ func NewLookup(hosts []string) Proxy {
 		Policy:      &Random{},
 		Spray:       nil,
 		FailTimeout: 10 * time.Second,
-		MaxFails:    3,
+		MaxFails:    3, // TODO(miek): disable error checking for simple lookups?
+		ex:          newDNSEx(),
 	}
 
 	for i, host := range hosts {
@@ -31,7 +31,6 @@ func NewLookup(hosts []string) Proxy {
 			Conns:       0,
 			Fails:       0,
 			FailTimeout: upstream.FailTimeout,
-			Exchanger:   newDNSEx(host),
 
 			Unhealthy: false,
 			CheckDown: func(upstream *staticUpstream) UpstreamHostDownFunc {
@@ -50,7 +49,7 @@ func NewLookup(hosts []string) Proxy {
 		}
 		upstream.Hosts[i] = uh
 	}
-	p.Upstreams = []Upstream{upstream}
+	p.Upstreams = &[]Upstream{upstream}
 	return p
 }
 
@@ -72,7 +71,7 @@ func (p Proxy) Forward(state request.Request) (*dns.Msg, error) {
 }
 
 func (p Proxy) lookup(state request.Request) (*dns.Msg, error) {
-	for _, upstream := range p.Upstreams {
+	for _, upstream := range *p.Upstreams {
 		start := time.Now()
 
 		// Since Select() should give us "up" hosts, keep retrying
@@ -88,7 +87,7 @@ func (p Proxy) lookup(state request.Request) (*dns.Msg, error) {
 
 			atomic.AddInt64(&host.Conns, 1)
 
-			reply, backendErr := host.Exchange(state)
+			reply, backendErr := upstream.Exchanger().Exchange(host.Name, state)
 
 			atomic.AddInt64(&host.Conns, -1)