diff --git a/cmd/clientsim/main.go b/cmd/clientsim/main.go
index ed090d3..f030d90 100644
--- a/cmd/clientsim/main.go
+++ b/cmd/clientsim/main.go
@@ -174,7 +174,7 @@ type ClientHandler struct {
 	caList   []string
 }
 
-func (c *ClientHandler) Send(ctx context.Context, command *protocol.Command, out chan []byte) error {
+func (c *ClientHandler) Send(ctx context.Context, command *protocol.Command, out chan<- []byte) error {
 	var (
 		frame []byte
 		err   error
@@ -213,7 +213,7 @@ func (c *ClientHandler) Send(ctx context.Context, command *protocol.Command, out
 	return nil
 }
 
-func (c *ClientHandler) ResponseAnnounce(ctx context.Context, in chan []byte) (*protocol.Response, error) {
+func (c *ClientHandler) ResponseAnnounce(ctx context.Context, in <-chan []byte) (*protocol.Response, error) {
 	response := &protocol.Response{}
 
 	var announce messages.ResponseAnnounce
@@ -236,7 +236,7 @@ func (c *ClientHandler) ResponseAnnounce(ctx context.Context, in chan []byte) (*
 	}
 }
 
-func (c *ClientHandler) ResponseData(ctx context.Context, in chan []byte, response *protocol.Response) error {
+func (c *ClientHandler) ResponseData(ctx context.Context, in <-chan []byte, response *protocol.Response) error {
 	select {
 	case <-ctx.Done():
 		return nil
diff --git a/cmd/signer/main.go b/cmd/signer/main.go
index 3c19600..c54ff41 100644
--- a/cmd/signer/main.go
+++ b/cmd/signer/main.go
@@ -116,18 +116,19 @@ func main() {
 		logger.WithError(err).Fatal("could not setup serial link handler")
 	}
 
-	defer func() { _ = serialHandler.Close() }()
-
 	logger.Info("setup complete, starting signer operation")
 
 	if err = runSigner(logger, serialHandler); err != nil {
-		logger.WithError(err).Fatal("error running serial handler")
+		logger.WithError(err).Error("error running serial handler")
+
+		os.Exit(1)
 	}
 }
 
 func runSigner(logger *logrus.Logger, serialHandler *serial.Handler) error {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
+	defer func() { _ = serialHandler.Close() }()
 
 	c := make(chan os.Signal, 1)
 	signal.Notify(c, os.Interrupt, syscall.SIGTERM)
diff --git a/internal/handler/msgpack.go b/internal/handler/msgpack.go
index 2963b92..67ac37f 100644
--- a/internal/handler/msgpack.go
+++ b/internal/handler/msgpack.go
@@ -46,7 +46,7 @@ type MsgPackHandler struct {
 	fetchCRLHandler                 *revoking.FetchCRLHandler
 }
 
-func (m *MsgPackHandler) CommandAnnounce(ctx context.Context, frames chan []byte) (*protocol.Command, error) {
+func (m *MsgPackHandler) CommandAnnounce(ctx context.Context, frames <-chan []byte) (*protocol.Command, error) {
 	select {
 	case <-ctx.Done():
 		return nil, nil
@@ -67,7 +67,7 @@ func (m *MsgPackHandler) CommandAnnounce(ctx context.Context, frames chan []byte
 	}
 }
 
-func (m *MsgPackHandler) CommandData(ctx context.Context, frames chan []byte, command *protocol.Command) error {
+func (m *MsgPackHandler) CommandData(ctx context.Context, frames <-chan []byte, command *protocol.Command) error {
 	select {
 	case <-ctx.Done():
 		return nil
@@ -106,7 +106,7 @@ func (m *MsgPackHandler) logCommandResponse(command *protocol.Command, response
 	m.logger.WithField("command", command).WithField("response", response).Debug("command and response")
 }
 
-func (m *MsgPackHandler) Respond(ctx context.Context, response *protocol.Response, out chan []byte) error {
+func (m *MsgPackHandler) Respond(ctx context.Context, response *protocol.Response, out chan<- []byte) error {
 	announce, err := msgpack.Marshal(response.Announce)
 	if err != nil {
 		return fmt.Errorf("could not marshal response announcement: %w", err)
diff --git a/pkg/protocol/protocol.go b/pkg/protocol/protocol.go
index 82d8c52..044c4d2 100644
--- a/pkg/protocol/protocol.go
+++ b/pkg/protocol/protocol.go
@@ -55,19 +55,19 @@ func (r *Response) String() string {
 // ServerHandler is responsible for parsing incoming frames and calling commands
 type ServerHandler interface {
 	// CommandAnnounce handles the initial announcement of a command.
-	CommandAnnounce(context.Context, chan []byte) (*Command, error)
+	CommandAnnounce(context.Context, <-chan []byte) (*Command, error)
 	// CommandData handles the command data.
-	CommandData(context.Context, chan []byte, *Command) error
+	CommandData(context.Context, <-chan []byte, *Command) error
 	// HandleCommand executes the command, generating a response.
 	HandleCommand(context.Context, *Command) (*Response, error)
 	// Respond generates the response for a command.
-	Respond(context.Context, *Response, chan []byte) error
+	Respond(context.Context, *Response, chan<- []byte) error
 }
 
 type ClientHandler interface {
-	Send(context.Context, *Command, chan []byte) error
-	ResponseAnnounce(context.Context, chan []byte) (*Response, error)
-	ResponseData(context.Context, chan []byte, *Response) error
+	Send(context.Context, *Command, chan<- []byte) error
+	ResponseAnnounce(context.Context, <-chan []byte) (*Response, error)
+	ResponseData(context.Context, <-chan []byte, *Response) error
 	HandleResponse(context.Context, *Response) error
 }
 
@@ -113,7 +113,8 @@ func (p protocolState) String() string {
 
 type ServerProtocol struct {
 	handler ServerHandler
-	in, out chan []byte
+	in      <-chan []byte
+	out     chan<- []byte
 	logger  *logrus.Logger
 	state   protocolState
 }
@@ -229,7 +230,7 @@ func (p *ServerProtocol) respond(ctx context.Context, response *Response) error
 	return nil
 }
 
-func NewServer(handler ServerHandler, in, out chan []byte, logger *logrus.Logger) *ServerProtocol {
+func NewServer(handler ServerHandler, in <-chan []byte, out chan<- []byte, logger *logrus.Logger) *ServerProtocol {
 	return &ServerProtocol{
 		handler: handler,
 		in:      in,
@@ -241,8 +242,9 @@ func NewServer(handler ServerHandler, in, out chan []byte, logger *logrus.Logger
 
 type ClientProtocol struct {
 	handler  ClientHandler
-	commands chan *Command
-	in, out  chan []byte
+	commands <-chan *Command
+	in       <-chan []byte
+	out      chan<- []byte
 	logger   *logrus.Logger
 	state    protocolState
 }
@@ -289,8 +291,8 @@ func (p *ClientProtocol) cmdAnnounce(ctx context.Context) error {
 	select {
 	case <-ctx.Done():
 		return nil
-	case command := <-p.commands:
-		if command == nil {
+	case command, ok := <-p.commands:
+		if !ok {
 			return errCommandExpected
 		}
 
@@ -300,6 +302,11 @@ func (p *ClientProtocol) cmdAnnounce(ctx context.Context) error {
 
 			return nil
 		}
+
+		p.logger.WithFields(map[string]interface{}{
+			"command":       command.Announce,
+			"buffer length": len(p.commands),
+		}).Trace("handled command")
 	}
 
 	p.state = respAnnounce
@@ -366,8 +373,9 @@ func (p *ClientProtocol) handleResponse(ctx context.Context, response *Response)
 
 func NewClient(
 	handler ClientHandler,
-	commands chan *Command,
-	in, out chan []byte,
+	commands <-chan *Command,
+	in <-chan []byte,
+	out chan<- []byte,
 	logger *logrus.Logger,
 ) *ClientProtocol {
 	return &ClientProtocol{
@@ -383,9 +391,9 @@ func NewClient(
 // Framer handles bytes on the wire by adding or removing framing information.
 type Framer interface {
 	// ReadFrames reads data frames and publishes unframed data to the channel.
-	ReadFrames(context.Context, io.Reader, chan []byte) error
+	ReadFrames(context.Context, io.Reader, chan<- []byte) error
 	// WriteFrames takes data from the channel and writes framed data to the writer.
-	WriteFrames(context.Context, io.Writer, chan []byte) error
+	WriteFrames(context.Context, io.Writer, <-chan []byte) error
 }
 
 const bufferSize = 1024
@@ -408,7 +416,7 @@ func NewCOBSFramer(logger *logrus.Logger) (*COBSFramer, error) {
 	}, nil
 }
 
-func (c *COBSFramer) ReadFrames(ctx context.Context, reader io.Reader, frameChan chan []byte) error {
+func (c *COBSFramer) ReadFrames(ctx context.Context, reader io.Reader, frameChan chan<- []byte) error {
 	var (
 		err              error
 		raw, data, frame []byte
@@ -496,7 +504,7 @@ func (c *COBSFramer) readRaw(ctx context.Context, reader io.Reader) ([]byte, err
 	}
 }
 
-func (c *COBSFramer) WriteFrames(ctx context.Context, writer io.Writer, frameChan chan []byte) error {
+func (c *COBSFramer) WriteFrames(ctx context.Context, writer io.Writer, frameChan <-chan []byte) error {
 	for {
 		select {
 		case <-ctx.Done():
diff --git a/pkg/protocol/protocol_test.go b/pkg/protocol/protocol_test.go
index 464fab3..a99fbdc 100644
--- a/pkg/protocol/protocol_test.go
+++ b/pkg/protocol/protocol_test.go
@@ -123,11 +123,11 @@ func TestProtocolState_String(t *testing.T) {
 
 type noopServerHandler struct{}
 
-func (h *noopServerHandler) CommandAnnounce(context.Context, chan []byte) (*Command, error) {
+func (h *noopServerHandler) CommandAnnounce(context.Context, <-chan []byte) (*Command, error) {
 	return nil, nil
 }
 
-func (h *noopServerHandler) CommandData(context.Context, chan []byte, *Command) error {
+func (h *noopServerHandler) CommandData(context.Context, <-chan []byte, *Command) error {
 	return nil
 }
 
@@ -135,7 +135,7 @@ func (h *noopServerHandler) HandleCommand(context.Context, *Command) (*Response,
 	return nil, nil
 }
 
-func (h *noopServerHandler) Respond(context.Context, *Response, chan []byte) error {
+func (h *noopServerHandler) Respond(context.Context, *Response, chan<- []byte) error {
 	return nil
 }
 
@@ -143,7 +143,7 @@ type testServerHandler struct {
 	logger *logrus.Logger
 }
 
-func (h *testServerHandler) CommandAnnounce(ctx context.Context, in chan []byte) (*Command, error) {
+func (h *testServerHandler) CommandAnnounce(ctx context.Context, in <-chan []byte) (*Command, error) {
 	select {
 	case <-ctx.Done():
 		return nil, nil
@@ -154,7 +154,7 @@ func (h *testServerHandler) CommandAnnounce(ctx context.Context, in chan []byte)
 	}
 }
 
-func (h *testServerHandler) CommandData(ctx context.Context, in chan []byte, command *Command) error {
+func (h *testServerHandler) CommandData(ctx context.Context, in <-chan []byte, command *Command) error {
 	select {
 	case <-ctx.Done():
 		return nil
@@ -176,7 +176,7 @@ func (h *testServerHandler) HandleCommand(_ context.Context, command *Command) (
 	}, nil
 }
 
-func (h *testServerHandler) Respond(ctx context.Context, response *Response, out chan []byte) error {
+func (h *testServerHandler) Respond(ctx context.Context, response *Response, out chan<- []byte) error {
 	h.logger.Info("send response")
 
 	buf := bytes.NewBuffer([]byte("test-response-"))
@@ -192,7 +192,7 @@ func (h *testServerHandler) Respond(ctx context.Context, response *Response, out
 
 type commandAnnounceErrServerHandler struct{ testServerHandler }
 
-func (h *commandAnnounceErrServerHandler) CommandAnnounce(ctx context.Context, in chan []byte) (*Command, error) {
+func (h *commandAnnounceErrServerHandler) CommandAnnounce(ctx context.Context, in <-chan []byte) (*Command, error) {
 	select {
 	case <-ctx.Done():
 		return nil, nil
@@ -203,7 +203,7 @@ func (h *commandAnnounceErrServerHandler) CommandAnnounce(ctx context.Context, i
 
 type commandAnnounceNilServerHandler struct{ testServerHandler }
 
-func (h *commandAnnounceNilServerHandler) CommandAnnounce(ctx context.Context, in chan []byte) (*Command, error) {
+func (h *commandAnnounceNilServerHandler) CommandAnnounce(ctx context.Context, in <-chan []byte) (*Command, error) {
 	select {
 	case <-ctx.Done():
 		return nil, nil
@@ -214,7 +214,7 @@ func (h *commandAnnounceNilServerHandler) CommandAnnounce(ctx context.Context, i
 
 type commandDataErrServerHandler struct{ testServerHandler }
 
-func (h *commandDataErrServerHandler) CommandData(ctx context.Context, in chan []byte, _ *Command) error {
+func (h *commandDataErrServerHandler) CommandData(ctx context.Context, in <-chan []byte, _ *Command) error {
 	select {
 	case <-ctx.Done():
 		return nil
@@ -226,8 +226,7 @@ func (h *commandDataErrServerHandler) CommandData(ctx context.Context, in chan [
 type commandDataNilAnnouncementServerHandler struct{ testServerHandler }
 
 func (h *commandDataNilAnnouncementServerHandler) CommandAnnounce(
-	ctx context.Context,
-	in chan []byte,
+	ctx context.Context, in <-chan []byte,
 ) (*Command, error) {
 	select {
 	case <-ctx.Done():
@@ -245,7 +244,7 @@ func (h *handleCommandErrServerHandler) HandleCommand(_ context.Context, command
 
 type handleCommandNilCommandServerHandler struct{ testServerHandler }
 
-func (h *handleCommandNilCommandServerHandler) CommandData(ctx context.Context, in chan []byte, _ *Command) error {
+func (h *handleCommandNilCommandServerHandler) CommandData(ctx context.Context, in <-chan []byte, _ *Command) error {
 	select {
 	case <-ctx.Done():
 		return nil
@@ -256,7 +255,7 @@ func (h *handleCommandNilCommandServerHandler) CommandData(ctx context.Context,
 
 type respondErrServerHandler struct{ testServerHandler }
 
-func (h *respondErrServerHandler) Respond(_ context.Context, r *Response, _ chan []byte) error {
+func (h *respondErrServerHandler) Respond(_ context.Context, r *Response, _ chan<- []byte) error {
 	return fmt.Errorf("failed to respond %s", r)
 }
 
@@ -914,15 +913,15 @@ func readServerResponse(ctx context.Context, out chan []byte) []byte {
 
 type noopClientHandler struct{}
 
-func (h *noopClientHandler) Send(context.Context, *Command, chan []byte) error {
+func (h *noopClientHandler) Send(context.Context, *Command, chan<- []byte) error {
 	return nil
 }
 
-func (h *noopClientHandler) ResponseAnnounce(context.Context, chan []byte) (*Response, error) {
+func (h *noopClientHandler) ResponseAnnounce(context.Context, <-chan []byte) (*Response, error) {
 	return nil, nil
 }
 
-func (h *noopClientHandler) ResponseData(context.Context, chan []byte, *Response) error {
+func (h *noopClientHandler) ResponseData(context.Context, <-chan []byte, *Response) error {
 	return nil
 }
 
@@ -932,7 +931,7 @@ func (h *noopClientHandler) HandleResponse(context.Context, *Response) error {
 
 type testClientHandler struct{ logger *logrus.Logger }
 
-func (h *testClientHandler) Send(ctx context.Context, command *Command, out chan []byte) error {
+func (h *testClientHandler) Send(ctx context.Context, command *Command, out chan<- []byte) error {
 	h.logger.Infof("send command %s", command.Announce.Code)
 
 	select {
@@ -957,7 +956,7 @@ func (h *testClientHandler) Send(ctx context.Context, command *Command, out chan
 	return nil
 }
 
-func (h *testClientHandler) ResponseAnnounce(ctx context.Context, in chan []byte) (*Response, error) {
+func (h *testClientHandler) ResponseAnnounce(ctx context.Context, in <-chan []byte) (*Response, error) {
 	select {
 	case <-ctx.Done():
 		return nil, nil
@@ -970,7 +969,7 @@ func (h *testClientHandler) ResponseAnnounce(ctx context.Context, in chan []byte
 	}
 }
 
-func (h *testClientHandler) ResponseData(ctx context.Context, in chan []byte, response *Response) error {
+func (h *testClientHandler) ResponseData(ctx context.Context, in <-chan []byte, response *Response) error {
 	select {
 	case <-ctx.Done():
 		return nil
@@ -991,7 +990,7 @@ func (h *testClientHandler) HandleResponse(_ context.Context, response *Response
 
 type commandAnnounceErrClientHandler struct{ testClientHandler }
 
-func (h *commandAnnounceErrClientHandler) Send(context.Context, *Command, chan []byte) error {
+func (h *commandAnnounceErrClientHandler) Send(context.Context, *Command, chan<- []byte) error {
 	return errors.New("failed sending command")
 }
 
@@ -1011,7 +1010,7 @@ func TestNewClient(t *testing.T) {
 
 type responseAnnounceErrClientHandler struct{ testClientHandler }
 
-func (h *responseAnnounceErrClientHandler) ResponseAnnounce(ctx context.Context, in chan []byte) (*Response, error) {
+func (h *responseAnnounceErrClientHandler) ResponseAnnounce(ctx context.Context, in <-chan []byte) (*Response, error) {
 	select {
 	case <-ctx.Done():
 		return nil, nil
@@ -1022,7 +1021,7 @@ func (h *responseAnnounceErrClientHandler) ResponseAnnounce(ctx context.Context,
 
 type responseAnnounceNilClientHandler struct{ testClientHandler }
 
-func (h *responseAnnounceNilClientHandler) ResponseAnnounce(ctx context.Context, in chan []byte) (*Response, error) {
+func (h *responseAnnounceNilClientHandler) ResponseAnnounce(ctx context.Context, in <-chan []byte) (*Response, error) {
 	select {
 	case <-ctx.Done():
 		return nil, nil
@@ -1033,7 +1032,7 @@ func (h *responseAnnounceNilClientHandler) ResponseAnnounce(ctx context.Context,
 
 type responseDataErrClientHandler struct{ testClientHandler }
 
-func (h *responseDataErrClientHandler) ResponseData(ctx context.Context, in chan []byte, _ *Response) error {
+func (h *responseDataErrClientHandler) ResponseData(ctx context.Context, in <-chan []byte, _ *Response) error {
 	select {
 	case <-ctx.Done():
 		return nil
@@ -1044,7 +1043,7 @@ func (h *responseDataErrClientHandler) ResponseData(ctx context.Context, in chan
 
 type responseDataTimeoutErrClientHandler struct{ testClientHandler }
 
-func (h *responseDataTimeoutErrClientHandler) ResponseData(ctx context.Context, in chan []byte, _ *Response) error {
+func (h *responseDataTimeoutErrClientHandler) ResponseData(ctx context.Context, in <-chan []byte, _ *Response) error {
 	select {
 	case <-ctx.Done():
 		return nil
@@ -1055,7 +1054,7 @@ func (h *responseDataTimeoutErrClientHandler) ResponseData(ctx context.Context,
 
 type responseDataNilClientHandler struct{ testClientHandler }
 
-func (h *responseDataNilClientHandler) ResponseData(ctx context.Context, in chan []byte, response *Response) error {
+func (h *responseDataNilClientHandler) ResponseData(ctx context.Context, in <-chan []byte, response *Response) error {
 	select {
 	case <-ctx.Done():
 		return nil
@@ -1194,6 +1193,7 @@ func TestClientProtocol_Handle(t *testing.T) { //nolint:cyclop
 
 		assertLogs(t, pHook, []expectedLogs{
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", cmdAnnounce)},
+			{logrus.TraceLevel, "handled command"},
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", respAnnounce)},
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", respData)},
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", handleResponse)},
@@ -1377,6 +1377,7 @@ func TestClientProtocol_Handle(t *testing.T) { //nolint:cyclop
 
 		assertLogs(t, pHook, []expectedLogs{
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", cmdAnnounce)},
+			{logrus.TraceLevel, "handled command"},
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", respAnnounce)},
 			{logrus.ErrorLevel, "could not handle response announce"},
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", cmdAnnounce)},
@@ -1441,6 +1442,7 @@ func TestClientProtocol_Handle(t *testing.T) { //nolint:cyclop
 
 		assertLogs(t, pHook, []expectedLogs{
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", cmdAnnounce)},
+			{logrus.TraceLevel, "handled command"},
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", respAnnounce)},
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", respData)},
 		})
@@ -1505,6 +1507,7 @@ func TestClientProtocol_Handle(t *testing.T) { //nolint:cyclop
 
 		assertLogs(t, pHook, []expectedLogs{
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", cmdAnnounce)},
+			{logrus.TraceLevel, "handled command"},
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", respAnnounce)},
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", respData)},
 			{logrus.ErrorLevel, "could not handle response data"},
@@ -1571,6 +1574,7 @@ func TestClientProtocol_Handle(t *testing.T) { //nolint:cyclop
 
 		assertLogs(t, pHook, []expectedLogs{
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", cmdAnnounce)},
+			{logrus.TraceLevel, "handled command"},
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", respAnnounce)},
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", respData)},
 			{logrus.ErrorLevel, "could not handle response data"},
@@ -1637,6 +1641,7 @@ func TestClientProtocol_Handle(t *testing.T) { //nolint:cyclop
 
 		assertLogs(t, pHook, []expectedLogs{
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", cmdAnnounce)},
+			{logrus.TraceLevel, "handled command"},
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", respAnnounce)},
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", respData)},
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", handleResponse)},
@@ -1703,6 +1708,7 @@ func TestClientProtocol_Handle(t *testing.T) { //nolint:cyclop
 
 		assertLogs(t, pHook, []expectedLogs{
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", cmdAnnounce)},
+			{logrus.TraceLevel, "handled command"},
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", respAnnounce)},
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", respData)},
 			{logrus.DebugLevel, fmt.Sprintf("handling protocol state %s", handleResponse)},