Pr 586 tweaks (#594)

* add proxy tcp

* add truncated for tcp to udp response

* move truncation to scrubbing

* add test that executes upstream over tcp

* middleware/proxy: some tweaks

rename force-tcp to force_tcp to be inline with the rest and use
a dnsOptions struct to put the options in to allow it to be extended.
Add some parse tests as well.

* Fix test and rename dnsOptions Options

middleware/proxy/dns.go

@@ -14,10 +14,19 @@ import (
 type dnsEx struct {
 	Timeout time.Duration
 	group   *singleflight.Group
+	Options
+}
+
+type Options struct {
+	ForceTCP bool // If true use TCP for upstream no matter what
 }
 
 func newDNSEx() *dnsEx {
-	return &dnsEx{group: new(singleflight.Group), Timeout: defaultTimeout * time.Second}
+	return newDNSExWithOption(Options{})
+}
+
+func newDNSExWithOption(opt Options) *dnsEx {
+	return &dnsEx{group: new(singleflight.Group), Timeout: defaultTimeout * time.Second, Options: opt}
 }
 
 func (d *dnsEx) Protocol() string          { return "dns" }
@@ -26,7 +35,11 @@ func (d *dnsEx) OnStartup(p *Proxy) error  { return nil }
 
 // Exchange implements the Exchanger interface.
 func (d *dnsEx) Exchange(ctx context.Context, addr string, state request.Request) (*dns.Msg, error) {
-	co, err := net.DialTimeout(state.Proto(), addr, d.Timeout)
+	proto := state.Proto()
+	if d.Options.ForceTCP {
+		proto = "tcp"
+	}
+	co, err := net.DialTimeout(proto, addr, d.Timeout)
 	if err != nil {
 		return nil, err
 	}
@@ -43,7 +56,8 @@ func (d *dnsEx) Exchange(ctx context.Context, addr string, state request.Request
 	if err != nil {
 		return nil, err
 	}
-
+	// Make sure it fits in the DNS response.
+	reply, _ = state.Scrub(reply)
 	reply.Compress = true
 	reply.Id = state.Req.Id