cmd/clientsim/main.go

@@ -20,14 +20,15 @@ limitations under the License.
 package main
 
 import (
+	"bytes"
 	"context"
-	"crypto/rand"
 	"fmt"
 	"io"
 	"os"
 	"sync"
 	"time"
 
+	"github.com/justincpresley/go-cobs"
 	"github.com/shamaton/msgpackgen/msgpack"
 	"github.com/sirupsen/logrus"
 
@@ -36,6 +37,8 @@ import (
 	"git.cacert.org/cacert-gosigner/pkg/messages"
 )
 
+var cobsConfig = cobs.Config{SpecialByte: protocol.CobsDelimiter, Delimiter: true, EndingSave: true}
+
 type protocolState int8
 
 const (
@@ -157,27 +160,16 @@ func (g *TestCommandGenerator) HandleResponse(frame []byte) error {
 }
 
 func (g *TestCommandGenerator) GenerateCommands(ctx context.Context) error {
+	const (
+		healthInterval = 5 * time.Second
+		startPause     = 3 * time.Second
+	)
+
 	var (
 		announce *messages.CommandAnnounce
 		err      error
 	)
 
-	// write some leading garbage to test signer robustness
-	_, _ = io.CopyN(os.Stdout, rand.Reader, 50) //nolint:gomnd
-
-	announce, err = messages.BuildCommandAnnounce(messages.CmdHealth)
-	if err != nil {
-		return fmt.Errorf("build command announce failed: %w", err)
-	}
-
-	g.commands <- &protocol.Command{Announce: announce, Command: &messages.HealthCommand{}}
-
-	const (
-		healthInterval = 5 * time.Second
-		crlInterval    = 15 * time.Minute
-		startPause     = 3 * time.Second
-	)
-
 	g.logger.Info("start generating commands")
 
 	time.Sleep(startPause)
@@ -192,18 +184,17 @@ func (g *TestCommandGenerator) GenerateCommands(ctx context.Context) error {
 		Command:  &messages.FetchCRLCommand{IssuerID: "sub-ecc_person_2022"},
 	}
 
-	healthTimer := time.NewTimer(healthInterval)
+	timer := time.NewTimer(healthInterval)
-	crlTimer := time.NewTimer(crlInterval)
 
 	for {
 		select {
 		case <-ctx.Done():
-			_ = healthTimer.Stop()
+			_ = timer.Stop()
 
 			g.logger.Info("stopping health check loop")
 
 			return nil
-		case <-healthTimer.C:
+		case <-timer.C:
 			announce, err = messages.BuildCommandAnnounce(messages.CmdHealth)
 			if err != nil {
 				return fmt.Errorf("build command announce failed: %w", err)
@@ -213,14 +204,9 @@ func (g *TestCommandGenerator) GenerateCommands(ctx context.Context) error {
 				Announce: announce,
 				Command:  &messages.HealthCommand{},
 			}
+		}
 
-			healthTimer.Reset(healthInterval)
+		timer.Reset(healthInterval)
-		case <-crlTimer.C:
-			g.commands <- &protocol.Command{
-				Announce: announce,
-				Command:  &messages.FetchCRLCommand{IssuerID: "sub-ecc_person_2022"},
-			}
-		}
 	}
 }
 
@@ -229,11 +215,106 @@ type clientSimulator struct {
 	logger           *logrus.Logger
 	lock             sync.Mutex
 	framesIn         chan []byte
-	framesOut        chan []byte
-	framer           protocol.Framer
 	commandGenerator *TestCommandGenerator
 }
 
+func (c *clientSimulator) readFrames() error {
+	const readInterval = 50 * time.Millisecond
+
+	var frame []byte
+
+	buffer := &bytes.Buffer{}
+
+	delimiter := []byte{cobsConfig.SpecialByte}
+
+	for {
+		readBytes, err := c.readFromStdin()
+		if err != nil {
+			c.logger.WithError(err).Error("stdin read error")
+
+			close(c.framesIn)
+
+			return err
+		}
+
+		if len(readBytes) == 0 {
+			time.Sleep(readInterval)
+
+			continue
+		}
+
+		c.logger.Tracef("read %d bytes", len(readBytes))
+
+		buffer.Write(readBytes)
+
+		c.logger.Tracef("read buffer is now %d bytes long", buffer.Len())
+
+		rest := buffer.Bytes()
+
+		if !bytes.Contains(rest, delimiter) {
+			c.logger.Tracef("read data does not contain the delimiter %x", delimiter)
+
+			continue
+		}
+
+		for bytes.Contains(rest, delimiter) {
+			parts := bytes.SplitAfterN(rest, delimiter, 2)
+			frame, rest = parts[0], parts[1]
+
+			c.logger.Tracef("frame of length %d", len(frame))
+
+			if len(frame) == 0 {
+				continue
+			}
+
+			err = cobs.Verify(frame, cobsConfig)
+			if err != nil {
+				return fmt.Errorf("frame verification failed: %w", err)
+			}
+
+			decoded := cobs.Decode(frame, cobsConfig)
+
+			c.logger.Tracef("frame decoded to length %d", len(decoded))
+
+			c.framesIn <- decoded
+
+			c.logger.Tracef("%d bytes remaining", len(rest))
+		}
+
+		buffer.Truncate(0)
+		buffer.Write(rest)
+
+		c.logger.Tracef("read buffer is now %d bytes long", buffer.Len())
+	}
+}
+
+func (c *clientSimulator) writeFrame(frame []byte) error {
+	encoded := cobs.Encode(frame, cobsConfig)
+
+	if _, err := io.Copy(os.Stdout, bytes.NewBuffer(encoded)); err != nil {
+		return fmt.Errorf("could not write data: %w", err)
+	}
+
+	return nil
+}
+
+func (c *clientSimulator) readFromStdin() ([]byte, error) {
+	const bufferSize = 1024
+
+	buf := make([]byte, bufferSize)
+
+	c.logger.Trace("waiting for input")
+
+	count, err := os.Stdin.Read(buf)
+	if err != nil {
+		return nil, fmt.Errorf("reading input failed: %w", err)
+	}
+
+	c.logger.Tracef("read %d bytes from stdin", count)
+
+	return buf[:count], nil
+}
+
 func (c *clientSimulator) writeCmdAnnouncement() error {
 	frame, err := c.commandGenerator.CmdAnnouncement()
 	if err != nil {
@@ -242,7 +323,9 @@ func (c *clientSimulator) writeCmdAnnouncement() error {
 
 	c.logger.Trace("writing command announcement")
 
-	c.framesOut <- frame
+	if err := c.writeFrame(frame); err != nil {
+		return err
+	}
 
 	if err := c.nextState(); err != nil {
 		return err
@@ -259,7 +342,9 @@ func (c *clientSimulator) writeCommand() error {
 
 	c.logger.Trace("writing command data")
 
-	c.framesOut <- frame
+	if err := c.writeFrame(frame); err != nil {
+		return err
+	}
 
 	if err := c.nextState(); err != nil {
 		return err
@@ -268,14 +353,11 @@ func (c *clientSimulator) writeCommand() error {
 	return nil
 }
 
-const responseAnnounceTimeout = 30 * time.Second
-const responseDataTimeout = 2 * time.Second
-
 func (c *clientSimulator) handleResponseAnnounce() error {
 	c.logger.Trace("waiting for response announce")
 
-	select {
+	frame := <-c.framesIn
-	case frame := <-c.framesIn:
+
 	if frame == nil {
 		return nil
 	}
@@ -287,13 +369,6 @@ func (c *clientSimulator) handleResponseAnnounce() error {
 	if err := c.nextState(); err != nil {
 		return err
 	}
-	case <-time.After(responseAnnounceTimeout):
-		c.logger.Warn("response announce timeout expired")
-
-		c.protocolState = cmdAnnounce
-
-		return nil
-	}
 
 	return nil
 }
@@ -301,8 +376,8 @@ func (c *clientSimulator) handleResponseAnnounce() error {
 func (c *clientSimulator) handleResponseData() error {
 	c.logger.Trace("waiting for response data")
 
-	select {
+	frame := <-c.framesIn
-	case frame := <-c.framesIn:
+
 	if frame == nil {
 		return nil
 	}
@@ -316,13 +391,6 @@ func (c *clientSimulator) handleResponseData() error {
 	}
 
 	return nil
-	case <-time.After(responseDataTimeout):
-		c.logger.Warn("response data timeout expired")
-
-		c.protocolState = cmdAnnounce
-
-		return nil
-	}
 }
 
 func (c *clientSimulator) Run(ctx context.Context) error {
@@ -330,13 +398,7 @@ func (c *clientSimulator) Run(ctx context.Context) error {
 	errors := make(chan error)
 
 	go func() {
-		err := c.framer.ReadFrames(os.Stdin, c.framesIn)
+		err := c.readFrames()
-
-		errors <- err
-	}()
-
-	go func() {
-		err := c.framer.WriteFrames(os.Stdout, c.framesOut)
 
 		errors <- err
 	}()
@@ -420,8 +482,6 @@ func main() {
 		},
 		logger:   logger,
 		framesIn: make(chan []byte),
-		framesOut: make(chan []byte),
-		framer:    protocol.NewCOBSFramer(logger),
 	}
 
 	err := sim.Run(context.Background())

internal/handler/msgpack.go

@@ -21,7 +21,6 @@ import (
 	"errors"
 	"fmt"
 	"sync"
-	"time"
 
 	"github.com/shamaton/msgpackgen/msgpack"
 	"github.com/sirupsen/logrus"
@@ -33,186 +32,185 @@ import (
 	"git.cacert.org/cacert-gosigner/pkg/messages"
 )
 
-const readCommandTimeOut = 5 * time.Second
+// MsgPackHandler is a Handler implementation for the msgpack serialization format.
-
-var errReadCommandTimeout = errors.New("read command timeout expired")
-
-// MsgPackHandler is a ServerHandler implementation for the msgpack serialization format.
 type MsgPackHandler struct {
 	logger          *logrus.Logger
 	healthHandler   *health.Handler
 	fetchCRLHandler *revoking.FetchCRLHandler
+	currentCommand  *protocol.Command
+	currentResponse *protocol.Response
 	lock            sync.Mutex
 }
 
-func (m *MsgPackHandler) CommandAnnounce(frames chan []byte) (*protocol.Command, error) {
+func (m *MsgPackHandler) HandleCommandAnnounce(frame []byte) error {
 	m.lock.Lock()
 	defer m.lock.Unlock()
 
-	frame := <-frames
-
 	var ann messages.CommandAnnounce
 
 	if err := msgpack.Unmarshal(frame, &ann); err != nil {
-		return nil, fmt.Errorf("could not unmarshal command announcement: %w", err)
+		return fmt.Errorf("could not unmarshal command announcement: %w", err)
 	}
 
 	m.logger.WithField("announcement", &ann).Info("received command announcement")
 
-	return &protocol.Command{Announce: &ann}, nil
+	m.currentCommand = &protocol.Command{Announce: &ann}
-}
-
-func (m *MsgPackHandler) CommandData(frames chan []byte, command *protocol.Command) error {
-	m.lock.Lock()
-	defer m.lock.Unlock()
-
-	select {
-	case frame := <-frames:
-		err := m.parseCommand(frame, command)
-		if err != nil {
-			return err
-		}
 
 	return nil
-	case <-time.After(readCommandTimeOut):
-		return errReadCommandTimeout
-	}
 }
 
-func (m *MsgPackHandler) HandleCommand(command *protocol.Command) (*protocol.Response, error) {
+func (m *MsgPackHandler) HandleCommand(frame []byte) error {
 	m.lock.Lock()
 	defer m.lock.Unlock()
 
-	var (
+	err := m.parseCommand(frame)
-		response *protocol.Response
+	if err != nil {
-		err      error
+		m.currentResponse = m.buildErrorResponse(err.Error())
-	)
 
-	response, err = m.handleCommand(command)
+		m.logCommandResponse()
+
+		return nil
+	}
+
+	err = m.handleCommand()
 	if err != nil {
 		m.logger.WithError(err).Error("command handling failed")
 
-		response = m.buildErrorResponse(command.Announce.ID, "command handling failed")
+		return err
 	}
 
-	m.logCommandResponse(command, response)
+	m.logCommandResponse()
 
-	return response, nil
+	m.currentCommand = nil
-}
-
-func (m *MsgPackHandler) logCommandResponse(command *protocol.Command, response *protocol.Response) {
-	m.logger.WithField("command", command.Announce).Info("handled command")
-	m.logger.WithField("command", command).WithField("response", response).Debug("command and response")
-}
-
-func (m *MsgPackHandler) Respond(response *protocol.Response, out chan []byte) error {
-	m.lock.Lock()
-	defer m.lock.Unlock()
-
-	announce, err := msgpack.Marshal(response)
-	if err != nil {
-		return fmt.Errorf("could not marshal response announcement: %w", err)
-	}
-
-	m.logger.WithField("length", len(announce)).Debug("write response announcement")
-
-	out <- announce
-
-	data, err := msgpack.Marshal(response.Response)
-	if err != nil {
-		return fmt.Errorf("could not marshal response: %w", err)
-	}
-
-	m.logger.WithField("length", len(data)).Debug("write response")
-
-	out <- announce
 
 	return nil
 }
 
-func (m *MsgPackHandler) parseHealthCommand(frame []byte) (*messages.HealthCommand, error) {
+func (m *MsgPackHandler) logCommandResponse() {
+	m.logger.WithField("command", m.currentCommand.Announce).Info("handled command")
+	m.logger.WithField(
+		"command",
+		m.currentCommand,
+	).WithField(
+		"response",
+		m.currentResponse,
+	).Debug("command and response")
+}
+
+func (m *MsgPackHandler) ResponseAnnounce() ([]byte, error) {
+	m.lock.Lock()
+	defer m.lock.Unlock()
+
+	announceData, err := msgpack.Marshal(m.currentResponse.Announce)
+	if err != nil {
+		return nil, fmt.Errorf("could not marshal response announcement: %w", err)
+	}
+
+	m.logger.WithField("announcement", m.currentResponse.Announce).Debug("write response announcement")
+
+	return announceData, nil
+}
+
+func (m *MsgPackHandler) ResponseData() ([]byte, error) {
+	m.lock.Lock()
+	defer m.lock.Unlock()
+
+	responseData, err := msgpack.Marshal(m.currentResponse.Response)
+	if err != nil {
+		return nil, fmt.Errorf("could not marshal response: %w", err)
+	}
+
+	m.logger.WithField("response", m.currentResponse.Response).Debug("write response")
+
+	return responseData, nil
+}
+
+func (m *MsgPackHandler) parseHealthCommand(frame []byte) error {
 	var command messages.HealthCommand
 
 	if err := msgpack.Unmarshal(frame, &command); err != nil {
 		m.logger.WithError(err).Error("unmarshal failed")
 
-		return nil, errors.New("could not unmarshal health command")
+		return errors.New("could not unmarshal health command")
 	}
 
-	return &command, nil
+	m.currentCommand.Command = &command
+
+	return nil
 }
 
-func (m *MsgPackHandler) parseFetchCRLCommand(frame []byte) (*messages.FetchCRLCommand, error) {
+func (m *MsgPackHandler) parseFetchCRLCommand(frame []byte) error {
 	var command messages.FetchCRLCommand
 
 	if err := msgpack.Unmarshal(frame, &command); err != nil {
 		m.logger.WithError(err).Error("unmarshal failed")
 
-		return nil, errors.New("could not unmarshal fetch crl command")
+		return errors.New("could not unmarshal fetch crl command")
 	}
 
-	return &command, nil
+	m.currentCommand.Command = &command
+
+	return nil
 }
 
-func (m *MsgPackHandler) handleCommand(command *protocol.Command) (*protocol.Response, error) {
+func (m *MsgPackHandler) currentID() string {
+	return m.currentCommand.Announce.ID
+}
+
+func (m *MsgPackHandler) handleCommand() error {
 	var (
-		responseCode messages.ResponseCode
+		err          error
 		responseData interface{}
+		responseCode messages.ResponseCode
 	)
 
-	switch cmd := command.Command.(type) {
+	switch m.currentCommand.Command.(type) {
 	case *messages.HealthCommand:
 		response, err := m.handleHealthCommand()
 		if err != nil {
-			return nil, err
+			return err
 		}
 
 		responseCode, responseData = messages.RespHealth, response
 	case *messages.FetchCRLCommand:
-		response, err := m.handleFetchCRLCommand(cmd)
+		response, err := m.handleFetchCRLCommand()
 		if err != nil {
-			return nil, err
+			return err
 		}
 
 		responseCode, responseData = messages.RespFetchCRL, response
 	default:
-		return nil, fmt.Errorf("unhandled command %s", command.Announce)
+		return fmt.Errorf("unhandled command %s", m.currentCommand.Announce)
 	}
 
-	return &protocol.Response{
+	if err != nil {
-		Announce: messages.BuildResponseAnnounce(responseCode, command.Announce.ID),
+		return fmt.Errorf("error from command handler: %w", err)
+	}
+
+	m.currentResponse = &protocol.Response{
+		Announce: messages.BuildResponseAnnounce(responseCode, m.currentID()),
 		Response: responseData,
-	}, nil
+	}
+
+	return nil
 }
 
-func (m *MsgPackHandler) buildErrorResponse(commandID string, errMsg string) *protocol.Response {
+func (m *MsgPackHandler) buildErrorResponse(errMsg string) *protocol.Response {
 	return &protocol.Response{
-		Announce: messages.BuildResponseAnnounce(messages.RespError, commandID),
+		Announce: messages.BuildResponseAnnounce(messages.RespError, m.currentID()),
 		Response: &messages.ErrorResponse{Message: errMsg},
 	}
 }
 
-func (m *MsgPackHandler) parseCommand(frame []byte, command *protocol.Command) error {
+func (m *MsgPackHandler) parseCommand(frame []byte) error {
-	switch command.Announce.Code {
+	switch m.currentCommand.Announce.Code {
 	case messages.CmdHealth:
-		healthCommand, err := m.parseHealthCommand(frame)
+		return m.parseHealthCommand(frame)
-		if err != nil {
-			return err
-		}
-
-		command.Command = healthCommand
 	case messages.CmdFetchCRL:
-		fetchCRLCommand, err := m.parseFetchCRLCommand(frame)
+		return m.parseFetchCRLCommand(frame)
-		if err != nil {
-			return err
-		}
-
-		command.Command = fetchCRLCommand
 	default:
-		return fmt.Errorf("unhandled command code %s", command.Announce.Code)
+		return fmt.Errorf("unhandled command code %s", m.currentCommand.Announce.Code)
 	}
-
-	return nil
 }
 
 func (m *MsgPackHandler) handleHealthCommand() (*messages.HealthResponse, error) {
@@ -237,20 +235,27 @@ func (m *MsgPackHandler) handleHealthCommand() (*messages.HealthResponse, error)
 	return response, nil
 }
 
-func (m *MsgPackHandler) handleFetchCRLCommand(command *messages.FetchCRLCommand) (*messages.FetchCRLResponse, error) {
+func (m *MsgPackHandler) handleFetchCRLCommand() (*messages.FetchCRLResponse, error) {
-	res, err := m.fetchCRLHandler.FetchCRL(command.IssuerID)
+	fetchCRLPayload, ok := m.currentCommand.Command.(*messages.FetchCRLCommand)
+	if !ok {
+		return nil, fmt.Errorf("could not use payload as FetchCRLPayload")
+	}
+
+	res, err := m.fetchCRLHandler.FetchCRL(fetchCRLPayload.IssuerID)
 	if err != nil {
 		return nil, fmt.Errorf("could not fetch CRL: %w", err)
 	}
 
-	return &messages.FetchCRLResponse{
+	response := &messages.FetchCRLResponse{
 		IsDelta:   false,
 		CRLNumber: res.Number,
 		CRLData:   res.CRLData,
-	}, nil
+	}
+
+	return response, nil
 }
 
-func New(logger *logrus.Logger, handlers ...RegisterHandler) (protocol.ServerHandler, error) {
+func New(logger *logrus.Logger, handlers ...RegisterHandler) (protocol.Handler, error) {
 	messages.RegisterGeneratedResolver()
 
 	h := &MsgPackHandler{

internal/serial/seriallink.go

@@ -15,14 +15,18 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-// Package serial provides a handler for the serial connection of the signer machine.
+// Package seriallink provides a handler for the serial connection of the signer machine.
 package serial
 
 import (
+	"bytes"
 	"context"
-	"errors"
 	"fmt"
+	"io"
+	"sync"
+	"time"
 
+	"github.com/justincpresley/go-cobs"
 	"github.com/sirupsen/logrus"
 	"github.com/tarm/serial"
 
@@ -35,15 +39,22 @@ type protocolState int8
 const (
 	cmdAnnounce protocolState = iota
 	cmdData
-	handleCommand
+	respAnnounce
-	respond
+	respData
 )
 
+var validTransitions = map[protocolState]protocolState{
+	cmdAnnounce:  cmdData,
+	cmdData:      respAnnounce,
+	respAnnounce: respData,
+	respData:     cmdAnnounce,
+}
+
 var protocolStateNames = map[protocolState]string{
 	cmdAnnounce:  "CMD ANNOUNCE",
 	cmdData:      "CMD DATA",
-	handleCommand: "RESP ANNOUNCE",
+	respAnnounce: "RESP ANNOUNCE",
-	respond:       "RESP DATA",
+	respData:     "RESP DATA",
 }
 
 func (p protocolState) String() string {
@@ -55,14 +66,13 @@ func (p protocolState) String() string {
 }
 
 type Handler struct {
-	protocolHandler protocol.ServerHandler
+	protocolHandler protocol.Handler
 	protocolState   protocolState
-	framer          protocol.Framer
 	config          *serial.Config
 	port            *serial.Port
 	logger          *logrus.Logger
+	lock            sync.Mutex
 	framesIn        chan []byte
-	framesOut       chan []byte
 }
 
 func (h *Handler) setupConnection() error {
@@ -85,137 +95,256 @@ func (h *Handler) Close() error {
 	return nil
 }
 
+var cobsConfig = cobs.Config{SpecialByte: protocol.CobsDelimiter, Delimiter: true, EndingSave: true}
+
 func (h *Handler) Run(ctx context.Context) error {
 	h.protocolState = cmdAnnounce
-	protocolErrors, framerErrors := make(chan error), make(chan error)
+	errors := make(chan error)
 
 	go func() {
-		err := h.framer.ReadFrames(h.port, h.framesIn)
+		err := h.readFrames()
 
-		framerErrors <- err
+		errors <- err
-	}()
-
-	go func() {
-		err := h.framer.WriteFrames(h.port, h.framesOut)
-
-		framerErrors <- err
-	}()
-
-	go func() {
-		err := h.handleProtocolState()
-
-		protocolErrors <- err
 	}()
 
 	for {
 		select {
 		case <-ctx.Done():
 			return nil
-		case err := <-framerErrors:
+
+		case err := <-errors:
 			if err != nil {
-				return fmt.Errorf("error from framer: %w", err)
+				return fmt.Errorf("error from handler loop: %w", err)
 			}
 
 			return nil
-		case err := <-protocolErrors:
-			if err != nil {
-				return fmt.Errorf("error from protocol handler: %w", err)
-			}
 
-			return nil
+		default:
+			if err := h.handleProtocolState(); err != nil {
+				return err
+			}
 		}
 	}
 }
 
-var errCommandExpected = errors.New("command must not be nil")
+func (h *Handler) readFrames() error {
-var errResponseExpected = errors.New("response must not be nil")
+	const (
-
+		readInterval = 50 * time.Millisecond
-func (h *Handler) handleProtocolState() error {
-	var (
-		command  *protocol.Command
-		response *protocol.Response
-		err      error
 	)
 
+	var frame []byte
+
+	buffer := &bytes.Buffer{}
+
+	delimiter := []byte{cobsConfig.SpecialByte}
+
 	for {
-		h.logger.Debugf("handling protocol state %s", h.protocolState)
+		readBytes, err := h.readFromPort()
+		if err != nil {
+			close(h.framesIn)
+
+			return err
+		}
+
+		if len(readBytes) == 0 {
+			time.Sleep(readInterval)
+
+			continue
+		}
+
+		h.logger.Tracef("read %d bytes", len(readBytes))
+
+		buffer.Write(readBytes)
+
+		h.logger.Tracef("read buffer is now %d bytes long", buffer.Len())
+
+		rest := buffer.Bytes()
+
+		if !bytes.Contains(rest, delimiter) {
+			continue
+		}
+
+		for bytes.Contains(rest, delimiter) {
+			parts := bytes.SplitAfterN(rest, delimiter, 2)
+			frame, rest = parts[0], parts[1]
+
+			h.logger.Tracef("frame of length %d", len(frame))
+
+			if len(frame) == 0 {
+				continue
+			}
+
+			if err := cobs.Verify(frame, cobsConfig); err != nil {
+				close(h.framesIn)
+
+				return fmt.Errorf("could not verify COBS frame: %w", err)
+			}
+
+			decoded := cobs.Decode(frame, cobsConfig)
+
+			h.logger.Tracef("frame decoded to length %d", len(decoded))
+
+			h.framesIn <- decoded
+		}
+
+		buffer.Truncate(0)
+		buffer.Write(rest)
+
+		h.logger.Tracef("read buffer is now %d bytes long", buffer.Len())
+	}
+}
+
+func (h *Handler) writeFrame(frame []byte) error {
+	encoded := cobs.Encode(frame, cobsConfig)
+
+	return h.writeToPort(encoded)
+}
+
+func (h *Handler) nextState() error {
+	next, ok := validTransitions[h.protocolState]
+	if !ok {
+		return fmt.Errorf("illegal protocol state %s", h.protocolState)
+	}
+
+	h.protocolState = next
+
+	return nil
+}
+
+func (h *Handler) handleProtocolState() error {
+	h.logger.Tracef("handling protocol state %s", h.protocolState)
+
+	h.lock.Lock()
+	defer h.lock.Unlock()
 
 	switch h.protocolState {
 	case cmdAnnounce:
-			command, err = h.protocolHandler.CommandAnnounce(h.framesIn)
+		if err := h.handleCmdAnnounce(); err != nil {
-			if err != nil {
+			return err
-				h.logger.WithError(err).Error("could not handle command announce")
-
-				break
 		}
-
-			h.protocolState = cmdData
 	case cmdData:
-			if command == nil {
+		if err := h.handleCmdData(); err != nil {
-				return errCommandExpected
+			return err
 		}
-
+	case respAnnounce:
-			err = h.protocolHandler.CommandData(h.framesIn, command)
+		if err := h.handleRespAnnounce(); err != nil {
-			if err != nil {
+			return err
-				h.logger.WithError(err).Error("could not handle command data")
-
-				h.protocolState = cmdAnnounce
-
-				break
 		}
-
+	case respData:
-			h.protocolState = handleCommand
+		if err := h.handleRespData(); err != nil {
-		case handleCommand:
+			return err
-			if command == nil {
-				return errCommandExpected
 		}
-
-			response, err = h.protocolHandler.HandleCommand(command)
-			if err != nil {
-				h.logger.WithError(err).Error("could not handle command")
-
-				h.protocolState = cmdAnnounce
-
-				break
-			}
-
-			command = nil
-
-			h.protocolState = respond
-		case respond:
-			if response == nil {
-				return errResponseExpected
-			}
-
-			err = h.protocolHandler.Respond(response, h.framesOut)
-			if err != nil {
-				h.logger.WithError(err).Error("could not respond")
-
-				h.protocolState = cmdAnnounce
-
-				break
-			}
-
-			response = nil
-
-			h.protocolState = cmdAnnounce
 	default:
 		return fmt.Errorf("unknown protocol state %s", h.protocolState)
 	}
-	}
+
+	return nil
 }
 
-func New(
+func (h *Handler) writeToPort(data []byte) error {
-	cfg *config.Serial,
+	reader := bytes.NewReader(data)
-	logger *logrus.Logger,
+
-	protocolHandler protocol.ServerHandler,
+	n, err := io.Copy(h.port, reader)
-) (*Handler, error) {
+	if err != nil {
+		return fmt.Errorf("could not write data: %w", err)
+	}
+
+	h.logger.Tracef("wrote %d bytes", n)
+
+	return nil
+}
+
+func (h *Handler) readFromPort() ([]byte, error) {
+	const bufferSize = 1024
+
+	buf := make([]byte, bufferSize)
+
+	count, err := h.port.Read(buf)
+	if err != nil {
+		return nil, fmt.Errorf("could not read from serial port: %w", err)
+	}
+
+	return buf[:count], nil
+}
+
+func (h *Handler) handleCmdAnnounce() error {
+	h.logger.Trace("waiting for command announce")
+
+	frame := <-h.framesIn
+	if frame == nil {
+		return nil
+	}
+
+	if err := h.protocolHandler.HandleCommandAnnounce(frame); err != nil {
+		return fmt.Errorf("command announce handling failed: %w", err)
+	}
+
+	if err := h.nextState(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (h *Handler) handleCmdData() error {
+	h.logger.Trace("waiting for command data")
+
+	frame := <-h.framesIn
+
+	if frame == nil {
+		return nil
+	}
+
+	if err := h.protocolHandler.HandleCommand(frame); err != nil {
+		return fmt.Errorf("command handler failed: %w", err)
+	}
+
+	if err := h.nextState(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (h *Handler) handleRespAnnounce() error {
+	frame, err := h.protocolHandler.ResponseAnnounce()
+	if err != nil {
+		return fmt.Errorf("could not get response announcement: %w", err)
+	}
+
+	if err := h.writeFrame(frame); err != nil {
+		return err
+	}
+
+	if err := h.nextState(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (h *Handler) handleRespData() error {
+	frame, err := h.protocolHandler.ResponseData()
+	if err != nil {
+		return fmt.Errorf("could not get response data: %w", err)
+	}
+
+	if err := h.writeFrame(frame); err != nil {
+		return err
+	}
+
+	if err := h.nextState(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func New(cfg *config.Serial, logger *logrus.Logger, protocolHandler protocol.Handler) (*Handler, error) {
 	h := &Handler{
 		protocolHandler: protocolHandler,
 		logger:          logger,
 		framesIn:        make(chan []byte),
-		framesOut:       make(chan []byte),
-		framer:          protocol.NewCOBSFramer(logger),
 	}
 	h.config = &serial.Config{Name: cfg.Device, Baud: cfg.Baud, ReadTimeout: cfg.Timeout}
 

pkg/messages/messages.go

@@ -43,7 +43,7 @@ const (
 
 var commandNames = map[CommandCode]string{
 	CmdHealth:   "HEALTH",
-	CmdFetchCRL: "FETCH CRL",
+	CmdFetchCRL: "FETCH URL",
 }
 
 func (c CommandCode) String() string {

pkg/protocol/protocol.go

@@ -19,14 +19,7 @@ limitations under the License.
 package protocol
 
 import (
-	"bytes"
-	"errors"
 	"fmt"
-	"io"
-	"time"
-
-	"github.com/justincpresley/go-cobs"
-	"github.com/sirupsen/logrus"
 
 	"git.cacert.org/cacert-gosigner/pkg/messages"
 )
@@ -51,130 +44,14 @@ func (r *Response) String() string {
 	return fmt.Sprintf("Rsp[announce={%s}, data={%s}]", r.Announce, r.Response)
 }
 
-// ServerHandler is responsible for parsing incoming frames and calling commands
+// Handler is responsible for parsing incoming frames and calling commands
-type ServerHandler interface {
+type Handler interface {
-	// CommandAnnounce handles the initial announcement of a command.
+	// HandleCommandAnnounce handles the initial announcement of a command.
-	CommandAnnounce(chan []byte) (*Command, error)
+	HandleCommandAnnounce([]byte) error
-	// CommandData handles the command data.
+	// HandleCommand handles the command data.
-	CommandData(chan []byte, *Command) error
+	HandleCommand([]byte) error
-	// HandleCommand executes the command, generating a response.
+	// ResponseAnnounce generates the announcement for a response.
-	HandleCommand(*Command) (*Response, error)
+	ResponseAnnounce() ([]byte, error)
-	// Respond generates the response for a command.
+	// ResponseData generates the response data.
-	Respond(*Response, chan []byte) error
+	ResponseData() ([]byte, error)
-}
-
-// 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(io.Reader, chan []byte) error
-	// WriteFrames takes data from the channel and writes framed data to the writer.
-	WriteFrames(io.Writer, chan []byte) error
-}
-
-const bufferSize = 1024
-const readInterval = 50 * time.Millisecond
-
-type COBSFramer struct {
-	config cobs.Config
-	logger *logrus.Logger
-}
-
-func NewCOBSFramer(logger *logrus.Logger) *COBSFramer {
-	return &COBSFramer{
-		config: cobs.Config{SpecialByte: CobsDelimiter, Delimiter: true, EndingSave: true},
-		logger: logger,
-	}
-}
-
-func (c *COBSFramer) ReadFrames(reader io.Reader, frameChan chan []byte) error {
-	var (
-		err              error
-		raw, data, frame []byte
-	)
-
-	buffer := &bytes.Buffer{}
-
-	for {
-		raw, err = c.readRaw(reader)
-		if err != nil {
-			close(frameChan)
-
-			return err
-		}
-
-		if len(raw) == 0 {
-			time.Sleep(readInterval)
-
-			continue
-		}
-
-		c.logger.Tracef("read %d raw bytes", len(raw))
-
-		buffer.Write(raw)
-
-		for {
-			data, err = buffer.ReadBytes(c.config.SpecialByte)
-			if err != nil {
-				if errors.Is(err, io.EOF) {
-					buffer.Write(data)
-
-					break
-				}
-
-				return fmt.Errorf("could not read from buffer: %w", err)
-			}
-
-			if err = cobs.Verify(data, c.config); err != nil {
-				c.logger.WithError(err).Warnf("skipping invalid frame of %d bytes", len(data))
-
-				break
-			}
-
-			frame = cobs.Decode(data, c.config)
-
-			c.logger.Tracef("frame decoded to length %d", len(frame))
-
-			frameChan <- frame
-		}
-
-		c.logger.Tracef("read buffer is now %d bytes long", buffer.Len())
-	}
-}
-
-func (c *COBSFramer) readRaw(reader io.Reader) ([]byte, error) {
-	buf := make([]byte, bufferSize)
-
-	count, err := reader.Read(buf)
-	if err != nil {
-		if errors.Is(err, io.EOF) {
-			return []byte{}, nil
-		}
-
-		return nil, fmt.Errorf("could not read data: %w", err)
-	}
-
-	raw := buf[:count]
-
-	return raw, nil
-}
-
-func (c *COBSFramer) WriteFrames(writer io.Writer, frameChan chan []byte) error {
-	for {
-		frame := <-frameChan
-
-		if frame == nil {
-			c.logger.Debug("channel closed")
-
-			return nil
-		}
-
-		encoded := cobs.Encode(frame, c.config)
-
-		n, err := io.Copy(writer, bytes.NewReader(encoded))
-		if err != nil {
-			return fmt.Errorf("cold not write data: %w", err)
-		}
-
-		c.logger.Tracef("wrote %d bytes", n)
-	}
 }