La context (#521)

* middleware/proxy: give Exchange a context

Make context.Context the first paramater in the Exchange method.
This is inline with all other query functions.

* up the version

.travis.yml

@@ -7,7 +7,7 @@ services:
 
 language: go
 go:
-  - 1.6
+  - 1.7
 
 go_import_path: github.com/miekg/coredns
 

middleware/proxy/dns.go

 package proxy
 
 import (
+	"context"
 	"net"
 	"time"
 
@@ -24,7 +25,7 @@ func (d *dnsEx) OnShutdown(p *Proxy) error { return nil }
 func (d *dnsEx) OnStartup(p *Proxy) error  { return nil }
 
 // Exchange implements the Exchanger interface.
-func (d *dnsEx) Exchange(addr string, state request.Request) (*dns.Msg, error) {
+func (d *dnsEx) Exchange(ctx context.Context, addr string, state request.Request) (*dns.Msg, error) {
 	co, err := net.DialTimeout(state.Proto(), addr, d.Timeout)
 	if err != nil {
 		return nil, err

middleware/proxy/exchanger.go

 package proxy
 
 import (
+	"context"
+
 	"github.com/miekg/coredns/request"
 	"github.com/miekg/dns"
 )
@@ -8,7 +10,7 @@ import (
 // Exchanger is an interface that specifies a type implementing a DNS resolver that
 // can use whatever transport it likes.
 type Exchanger interface {
-	Exchange(addr string, state request.Request) (*dns.Msg, error)
+	Exchange(ctx context.Context, addr string, state request.Request) (*dns.Msg, error)
 	Protocol() string
 
 	OnStartup(*Proxy) error

middleware/proxy/google.go

 package proxy
 
 import (
+	"context"
 	"crypto/tls"
 	"encoding/json"
 	"fmt"
@@ -42,7 +43,7 @@ func newGoogle(endpoint string, bootstrap []string) *google {
 	return &google{client: client, endpoint: dns.Fqdn(endpoint), bootstrapProxy: boot, quit: make(chan bool)}
 }
 
-func (g *google) Exchange(addr string, state request.Request) (*dns.Msg, error) {
+func (g *google) Exchange(ctx context.Context, addr string, state request.Request) (*dns.Msg, error) {
 	v := url.Values{}
 
 	v.Set("name", state.Name())

middleware/proxy/lookup.go

@@ -3,6 +3,7 @@ package proxy
 // functions other middleware might want to use to do lookup in the same style as the proxy.
 
 import (
+	"context"
 	"sync/atomic"
 	"time"
 
@@ -91,7 +92,7 @@ func (p Proxy) lookup(state request.Request) (*dns.Msg, error) {
 
 			atomic.AddInt64(&host.Conns, 1)
 
-			reply, backendErr := upstream.Exchanger().Exchange(host.Name, state)
+			reply, backendErr := upstream.Exchanger().Exchange(context.TODO(), host.Name, state)
 
 			atomic.AddInt64(&host.Conns, -1)
 

middleware/proxy/proxy.go

@@ -105,7 +105,7 @@ func (p Proxy) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (
 
 			atomic.AddInt64(&host.Conns, 1)
 
-			reply, backendErr := upstream.Exchanger().Exchange(host.Name, state)
+			reply, backendErr := upstream.Exchanger().Exchange(ctx, host.Name, state)
 
 			atomic.AddInt64(&host.Conns, -1)