plugin/forward: add prefer_udp option (#1944)

* plugin/forward: add prefer_udp option

* updated according to code review

 - fixed linter warning
 - removed metric parameter in Proxy.Connect()

1 files changed, 31 insertions, 4 deletions

diff --git a/plugin/forward/proxy_test.go b/plugin/forward/proxy_test.go
index 01e8ef6fd..d68d1def2 100644
--- a/plugin/forward/proxy_test.go
+++ b/plugin/forward/proxy_test.go
@@ -29,10 +29,10 @@ func TestProxyClose(t *testing.T) {
 		p := NewProxy(s.Addr, nil)
 		p.start(hcInterval)
 
-		go func() { p.Connect(ctx, state, false, false) }()
-		go func() { p.Connect(ctx, state, true, false) }()
-		go func() { p.Connect(ctx, state, false, false) }()
-		go func() { p.Connect(ctx, state, true, false) }()
+		go func() { p.Connect(ctx, state, options{}) }()
+		go func() { p.Connect(ctx, state, options{forceTCP: true}) }()
+		go func() { p.Connect(ctx, state, options{}) }()
+		go func() { p.Connect(ctx, state, options{forceTCP: true}) }()
 
 		p.close()
 	}
@@ -93,3 +93,30 @@ func TestProxyTLSFail(t *testing.T) {
 		t.Fatal("Expected *not* to receive reply, but got one")
 	}
 }
+
+func TestProtocolSelection(t *testing.T) {
+	p := NewProxy("bad_address", nil)
+
+	stateUDP := request.Request{W: &test.ResponseWriter{}, Req: new(dns.Msg)}
+	stateTCP := request.Request{W: &test.ResponseWriter{TCP: true}, Req: new(dns.Msg)}
+	ctx := context.TODO()
+
+	go func() {
+		p.Connect(ctx, stateUDP, options{})
+		p.Connect(ctx, stateUDP, options{forceTCP: true})
+		p.Connect(ctx, stateUDP, options{preferUDP: true})
+		p.Connect(ctx, stateUDP, options{preferUDP: true, forceTCP: true})
+		p.Connect(ctx, stateTCP, options{})
+		p.Connect(ctx, stateTCP, options{forceTCP: true})
+		p.Connect(ctx, stateTCP, options{preferUDP: true})
+		p.Connect(ctx, stateTCP, options{preferUDP: true, forceTCP: true})
+	}()
+
+	for i, exp := range []string{"udp", "tcp", "udp", "tcp", "tcp", "tcp", "udp", "tcp"} {
+		proto := <-p.transport.dial
+		p.transport.ret <- nil
+		if proto != exp {
+			t.Errorf("Unexpected protocol in case %d, expected %q, actual %q", i, exp, proto)
+		}
+	}
+}