Add SKIP policy to not expect a PROXY header

policy.go

@@ -32,8 +32,31 @@ const (
 	// a PROXY header is not present, subsequent reads do not. It is the task
 	// of the code using the connection to handle that case properly.
 	REQUIRE
+	// SKIP accepts a connection without requiring the PROXY header
+	// Note: an example usage can be found in the SkipProxyHeaderForCIDR
+	// function.
+	SKIP
 )
 
+// SkipProxyHeaderForCIDR returns a PolicyFunc which can be used to accept a
+// connection from a skipHeaderCIDR without requiring a PROXY header, e.g.
+// Kubernetes pods local traffic. The def is a policy to use when an upstream
+// address doesn't match the skipHeaderCIDR.
+func SkipProxyHeaderForCIDR(skipHeaderCIDR *net.IPNet, def Policy) PolicyFunc {
+	return func(upstream net.Addr) (Policy, error) {
+		ip, err := ipFromAddr(upstream)
+		if err != nil {
+			return def, err
+		}
+
+		if skipHeaderCIDR != nil && skipHeaderCIDR.Contains(ip) {
+			return SKIP, nil
+		}
+
+		return def, nil
+	}
+}
+
 // WithPolicy adds given policy to a connection when passed as option to NewConn()
 func WithPolicy(p Policy) func(*Conn) {
 	return func(c *Conn) {

policy_test.go

@@ -188,3 +188,26 @@ func Test_MustStrictWhiteListPolicyPanicsWithInvalidIpRange(t *testing.T) {
 
 	MustStrictWhiteListPolicy([]string{"20/80"})
 }
+
+func TestSkipProxyHeaderForCIDR(t *testing.T) {
+	_, cidr, _ := net.ParseCIDR("192.0.2.1/24")
+	f := SkipProxyHeaderForCIDR(cidr, REJECT)
+
+	upstream, _ := net.ResolveTCPAddr("tcp", "192.0.2.255:12345")
+	policy, err := f(upstream)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	if policy != SKIP {
+		t.Errorf("Expected a SKIP policy for the %s address", upstream)
+	}
+
+	upstream, _ = net.ResolveTCPAddr("tcp", "8.8.8.8:12345")
+	policy, err = f(upstream)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	if policy != REJECT {
+		t.Errorf("Expected a REJECT policy for the %s address", upstream)
+	}
+}

protocol.go

@@ -74,6 +74,10 @@ func (p *Listener) Accept() (net.Conn, error) {
 			conn.Close()
 			return nil, err
 		}
+		// Handle a connection as a regular one
+		if proxyHeaderPolicy == SKIP {
+			return conn, nil
+		}
 	}
 
 	newConn := NewConn(

protocol_test.go

@@ -923,6 +923,59 @@ func TestReadingIsRefusedOnErrorWhenLocalAddrRequestedFirst(t *testing.T) {
 	}
 }
 
+func TestSkipProxyProtocolPolicy(t *testing.T) {
+	l, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	policyFunc := func(upstream net.Addr) (Policy, error) { return SKIP, nil }
+
+	pl := &Listener{
+		Listener: l,
+		Policy:   policyFunc,
+	}
+
+	cliResult := make(chan error)
+	ping := []byte("ping")
+	go func() {
+		conn, err := net.Dial("tcp", pl.Addr().String())
+		if err != nil {
+			cliResult <- err
+			return
+		}
+		defer conn.Close()
+		conn.Write(ping)
+		close(cliResult)
+	}()
+
+	conn, err := pl.Accept()
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	defer conn.Close()
+
+	_, ok := conn.(*net.TCPConn)
+	if !ok {
+		t.Fatal("err: should be a tcp connection")
+	}
+	_ = conn.LocalAddr()
+	recv := make([]byte, 4)
+	_, err = conn.Read(recv)
+	if err != nil {
+		t.Fatalf("Unexpected read error: %v", err)
+	}
+
+	if !bytes.Equal(ping, recv) {
+		t.Fatalf("Unexpected %s data while expected %s", recv, ping)
+	}
+
+	err = <-cliResult
+	if err != nil {
+		t.Fatalf("client error: %v", err)
+	}
+}
+
 func Test_ConnectionCasts(t *testing.T) {
 	l, err := net.Listen("tcp", "127.0.0.1:0")
 	if err != nil {