Add optional support for the PROXY protocol

This adds support for the commonly implemented PROXY protocol, allowing
TCP proxies to pass along upstream client information. When this is
enabled gorouter will read the PROXY preamble and inject the upstream
information into the X-Forwarded-For header.

http://blog.haproxy.com/haproxy/proxy-protocol/

config/config.go

@@ -87,6 +87,7 @@ type Config struct {
 	AccessLog                AccessLog     `yaml:"access_log"`
 	EnableAccessLogStreaming bool          `yaml:"enable_access_log_streaming"`
 	DebugAddr                string        `yaml:"debug_addr"`
+	EnablePROXY              bool          `yaml:"enable_proxy"`
 	EnableSSL                bool          `yaml:"enable_ssl"`
 	SSLPort                  uint16        `yaml:"ssl_port"`
 	SSLCertPath              string        `yaml:"ssl_cert_path"`
@@ -141,11 +142,12 @@ var defaultConfig = Config{
 	Nats:    []NatsConfig{defaultNatsConfig},
 	Logging: defaultLoggingConfig,
 
-	Port:       8081,
-	Index:      0,
-	GoMaxProcs: -1,
-	EnableSSL:  false,
-	SSLPort:    443,
+	Port:        8081,
+	Index:       0,
+	GoMaxProcs:  -1,
+	EnablePROXY: false,
+	EnableSSL:   false,
+	SSLPort:     443,
 
 	EndpointTimeoutInSeconds:     60,
 	RouteServiceTimeoutInSeconds: 60,

config/config_test.go

@@ -265,6 +265,16 @@ token_fetcher_expiration_buffer_time: 40
 			Expect(config.TokenFetcherRetryIntervalInSeconds).To(Equal(5))
 			Expect(config.TokenFetcherExpirationBufferTimeInSeconds).To(Equal(int64(30)))
 		})
+
+		It("sets proxy protocol", func() {
+			var b = []byte(`
+enable_proxy: true
+`)
+
+			config.Initialize(b)
+
+			Expect(config.EnablePROXY).To(Equal(true))
+		})
 	})
 
 	Describe("Process", func() {

router/router.go

@@ -7,6 +7,7 @@ import (
 	"sync"
 	"syscall"
 
+	"github.com/armon/go-proxyproto"
 	"github.com/apcera/nats"
 	"github.com/cloudfoundry/dropsonde"
 	vcap "github.com/cloudfoundry/gorouter/common"
@@ -267,10 +268,14 @@ func (r *Router) serveHTTPS(server *http.Server, errChan chan error) error {
 		}
 
 		r.tlsListener = tlsListener
-		r.logger.Info(fmt.Sprintf("Listening on %s", tlsListener.Addr()))
+		if r.config.EnablePROXY {
+			r.tlsListener = &proxyproto.Listener{tlsListener}
+		}
+
+		r.logger.Info(fmt.Sprintf("Listening on %s", r.tlsListener.Addr()))
 
 		go func() {
-			err := server.Serve(tlsListener)
+			err := server.Serve(r.tlsListener)
 			r.stopLock.Lock()
 			if !r.stopping {
 				errChan <- err
@@ -290,10 +295,14 @@ func (r *Router) serveHTTP(server *http.Server, errChan chan error) error {
 	}
 
 	r.listener = listener
-	r.logger.Info(fmt.Sprintf("Listening on %s", listener.Addr()))
+	if r.config.EnablePROXY {
+		r.listener = &proxyproto.Listener{listener}
+	}
+
+	r.logger.Info(fmt.Sprintf("Listening on %s", r.listener.Addr()))
 
 	go func() {
-		err := server.Serve(listener)
+		err := server.Serve(r.listener)
 		r.stopLock.Lock()
 		if !r.stopping {
 			errChan <- err