Add optional timeout to get PROXY header

The library user can define a maximum time to wait
for the PROXY protocol header, before failing out to
normal connection.

We can assume that a proxy in front of the service will
send the PROXY header immediatelly.

This solves the issue of clients getting block when
getting the RemoteAddr() for an incoming connection that
does not send any data. That is the case of http.Serve on
go < 1.6 as described in https://github.com/armon/go-proxyproto/issues/1

protocol_test.go

@@ -5,6 +5,7 @@ import (
 	"io"
 	"net"
 	"testing"
+	"time"
 )
 
 func TestPassthrough(t *testing.T) {
@@ -13,7 +14,7 @@ func TestPassthrough(t *testing.T) {
 		t.Fatalf("err: %v", err)
 	}
 
-	pl := &Listener{l}
+	pl := &Listener{Listener: l}
 
 	go func() {
 		conn, err := net.Dial("tcp", pl.Addr().String())
@@ -53,13 +54,77 @@ func TestPassthrough(t *testing.T) {
 	}
 }
 
+func TestTimeout(t *testing.T) {
+	l, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	clientWriteDelay := 200 * time.Millisecond
+	proxyHeaderTimeout := 50 * time.Millisecond
+	pl := &Listener{Listener: l, ProxyHeaderTimeout: proxyHeaderTimeout}
+
+	go func() {
+		conn, err := net.Dial("tcp", pl.Addr().String())
+		if err != nil {
+			t.Fatalf("err: %v", err)
+		}
+		defer conn.Close()
+
+		// Do not send data for a while
+		time.Sleep(clientWriteDelay)
+
+		conn.Write([]byte("ping"))
+		recv := make([]byte, 4)
+		_, err = conn.Read(recv)
+		if err != nil {
+			t.Fatalf("err: %v", err)
+		}
+		if !bytes.Equal(recv, []byte("pong")) {
+			t.Fatalf("bad: %v", recv)
+		}
+	}()
+
+	conn, err := pl.Accept()
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	defer conn.Close()
+
+	// Check the remote addr is the original 127.0.0.1
+	remoteAddrStartTime := time.Now()
+	addr := conn.RemoteAddr().(*net.TCPAddr)
+	if addr.IP.String() != "127.0.0.1" {
+		t.Fatalf("bad: %v", addr)
+	}
+	remoteAddrDuration := time.Since(remoteAddrStartTime)
+
+	// Check RemoteAddr() call did timeout
+	if remoteAddrDuration >= clientWriteDelay {
+		t.Fatalf("RemoteAddr() took longer than the specified timeout: %v < %v", proxyHeaderTimeout, remoteAddrDuration)
+	}
+
+	recv := make([]byte, 4)
+	_, err = conn.Read(recv)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	if !bytes.Equal(recv, []byte("ping")) {
+		t.Fatalf("bad: %v", recv)
+	}
+
+	if _, err := conn.Write([]byte("pong")); err != nil {
+		t.Fatalf("err: %v", err)
+	}
+}
+
 func TestParse_ipv4(t *testing.T) {
 	l, err := net.Listen("tcp", "127.0.0.1:0")
 	if err != nil {
 		t.Fatalf("err: %v", err)
 	}
 
-	pl := &Listener{l}
+	pl := &Listener{Listener: l}
 
 	go func() {
 		conn, err := net.Dial("tcp", pl.Addr().String())
@@ -118,7 +183,7 @@ func TestParse_ipv6(t *testing.T) {
 		t.Fatalf("err: %v", err)
 	}
 
-	pl := &Listener{l}
+	pl := &Listener{Listener: l}
 
 	go func() {
 		conn, err := net.Dial("tcp", pl.Addr().String())
@@ -177,7 +242,7 @@ func TestParse_BadHeader(t *testing.T) {
 		t.Fatalf("err: %v", err)
 	}
 
-	pl := &Listener{l}
+	pl := &Listener{Listener: l}
 
 	go func() {
 		conn, err := net.Dial("tcp", pl.Addr().String())