Add support for validating the downstream ip of the connection

Author: kmala

protocol.go

@@ -25,6 +25,7 @@ var DefaultReadHeaderTimeout = 10 * time.Second
 type Listener struct {
 	Listener          net.Listener
 	Policy            PolicyFunc
+	DownstreamPolicy  PolicyFunc
 	ValidateHeader    Validator
 	ReadHeaderTimeout time.Duration
 }
@@ -79,6 +80,18 @@ func (p *Listener) Accept() (net.Conn, error) {
 			return conn, nil
 		}
 	}
+	if p.DownstreamPolicy != nil {
+		proxyHeaderPolicy, err = p.DownstreamPolicy(conn.LocalAddr())
+		if err != nil {
+			// can't decide the policy, we can't accept the connection
+			conn.Close()
+			return nil, err
+		}
+		// Handle a connection as a regular one
+		if proxyHeaderPolicy == SKIP {
+			return conn, nil
+		}
+	}
 
 	newConn := NewConn(
 		conn,

protocol_test.go

@@ -857,6 +857,91 @@ func TestIgnorePolicyIgnoresIpFromProxyHeader(t *testing.T) {
 	}
 }
 
+func TestIgnoreUpstreamPolicyIgnoresIpFromProxyHeader(t *testing.T) {
+	l, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	policyFunc := func(downstream net.Addr) (Policy, error) { return IGNORE, nil }
+
+	pl := &Listener{Listener: l, DownstreamPolicy: policyFunc}
+
+	cliResult := make(chan error)
+	go func() {
+		conn, err := net.Dial("tcp", pl.Addr().String())
+		if err != nil {
+			cliResult <- err
+			return
+		}
+		defer conn.Close()
+
+		// Write out the header!
+		header := &Header{
+			Version:           2,
+			Command:           PROXY,
+			TransportProtocol: TCPv4,
+			SourceAddr: &net.TCPAddr{
+				IP:   net.ParseIP("10.1.1.1"),
+				Port: 1000,
+			},
+			DestinationAddr: &net.TCPAddr{
+				IP:   net.ParseIP("20.2.2.2"),
+				Port: 2000,
+			},
+		}
+		if _, err := header.WriteTo(conn); err != nil {
+			cliResult <- err
+			return
+		}
+
+		if _, err := conn.Write([]byte("ping")); err != nil {
+			cliResult <- err
+			return
+		}
+
+		recv := make([]byte, 4)
+		if _, err = conn.Read(recv); err != nil {
+			cliResult <- err
+			return
+		}
+		if !bytes.Equal(recv, []byte("pong")) {
+			cliResult <- fmt.Errorf("bad: %v", recv)
+			return
+		}
+
+		close(cliResult)
+	}()
+
+	conn, err := pl.Accept()
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	defer conn.Close()
+
+	recv := make([]byte, 4)
+	if _, err = conn.Read(recv); 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)
+	}
+
+	// Check the remote addr
+	addr := conn.RemoteAddr().(*net.TCPAddr)
+	if addr.IP.String() != "127.0.0.1" {
+		t.Fatalf("bad: %v", addr)
+	}
+	err = <-cliResult
+	if err != nil {
+		t.Fatalf("client error: %v", err)
+	}
+}
+
 func Test_AllOptionsAreRecognized(t *testing.T) {
 	recognizedOpt1 := false
 	opt1 := func(c *Conn) {