Upstream plugin prototype

upstream/upstream.go

@@ -0,0 +1,43 @@
+package upstream
+
+import (
+	"github.com/coredns/coredns/plugin"
+	"github.com/miekg/dns"
+	"github.com/pkg/errors"
+	"golang.org/x/net/context"
+	"time"
+)
+
+const (
+	defaultTimeout = 5 * time.Second
+)
+
+// Upstream is a simplified interface for proxy destination
+type Upstream interface {
+	Exchange(ctx context.Context, query *dns.Msg) (*dns.Msg, error)
+}
+
+// UpstreamPlugin is a simplified DNS proxy using a generic upstream interface
+type UpstreamPlugin struct {
+	Upstreams []Upstream
+	Next      plugin.Handler
+}
+
+// ServeDNS implements interface for CoreDNS plugin
+func (p UpstreamPlugin) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+	var reply *dns.Msg
+	var backendErr error
+
+	for _, upstream := range p.Upstreams {
+		reply, backendErr = upstream.Exchange(ctx, r)
+		if backendErr == nil {
+			w.WriteMsg(reply)
+			return 0, nil
+		}
+	}
+
+	return dns.RcodeServerFailure, errors.Wrap(backendErr, "failed to contact any of the upstreams")
+}
+
+// Name implements interface for CoreDNS plugin
+func (p UpstreamPlugin) Name() string { return "upstream" }