cacert-gosigner/signer/main.go

package main

import (
	"errors"
	"flag"
	"fmt"
	"time"

	log "github.com/sirupsen/logrus"
	"go.bug.st/serial"

	"git.cacert.org/cacert-gosigner/datastructures"
	"git.cacert.org/cacert-gosigner/shared"
)

var (
	address  string
	baudrate int
)

func main() {
	flag.StringVar(&address, "a", "/dev/ttyUSB0", "address")
	flag.IntVar(&baudrate, "b", 115200, "baud rate")
	flag.Parse()

	serialMode := &serial.Mode{
		BaudRate: baudrate,
		DataBits: 8,
		StopBits: serial.OneStopBit,
		Parity:   serial.NoParity,
	}
	log.Infof("connecting to %s using %+v", address, serialMode)
	port, err := serial.Open(address, serialMode)
	if err != nil {
		log.Fatal(err)
	}
	log.Println("connected")

	count := 0

	defer func() {
		err := port.Close()
		if err != nil {
			log.Fatal(err)
		}
		log.Println("closed")
	}()

readLoop:
	for {
		// timeout if no command has been received within 15 seconds
		timeout := time.After(15 * time.Second)

		commandChan := make(chan datastructures.SignerRequest, 1)
		errChan := make(chan error, 1)
		go Receive(&port, &commandChan, &errChan)

		select {
		case command := <-commandChan:
			response, err := Process(command)
			if err != nil {
				log.Printf("ERROR %v\n", err)
			} else {
				_ = SendResponse(&port, response)
			}
		case <-timeout:
			log.Println("timeout in main loop")
			break readLoop
		case err := <-errChan:
			log.Printf("ERROR %v\n", err)
		}

		count++
		log.Printf("INFO %d requests processed. Waiting for next request ...\n", count)
	}
}

// Send a response to the client
func SendResponse(port *serial.Port, response *datastructures.SignerResponse) error {
	if _, err := (*port).Write([]byte{0x02}); err != nil {
		return err
	}

	if ack, err := shared.ReceiveBytes(port, 1, 5); err != nil {
		return err
	} else if ack[0] != 0x10 {
		return errors.New(fmt.Sprintf("invalid ack byte 0x%02x", ack[0]))
	}

	tryAgain := true
	for tryAgain {
		data := response.Serialize()
		if _, err := (*port).Write(data); err != nil {
			return err
		}

		checksum := datastructures.CalculateXorCheckSum([][]byte{data})
		if _, err := (*port).Write([]byte{checksum}); err != nil {
			return err
		}

		if _, err := (*port).Write([]byte(shared.MagicTrailer)); err != nil {
			return err
		}

		if ack, err := shared.ReceiveBytes(port, 1, 5); err != nil {
			return err
		} else if ack[0] == 0x10 {
			tryAgain = false
		} else if ack[0] != 0x11 {
			return errors.New(fmt.Sprintf("invalid ack byte 0x%02x", ack[0]))
		}
	}

	return nil
}

// Process the signer request
func Process(command datastructures.SignerRequest) (response *datastructures.SignerResponse, err error) {
	log.Printf("INFO analyze %+v\n", command)

	switch command.Action {
	case datastructures.ActionNul:
		response, err = handleNulAction(command)
		return
	default:
		return nil, errors.New(fmt.Sprintf("unsupported Action 0x%02x", command.Action))
	}
}

func handleNulAction(command datastructures.SignerRequest) (*datastructures.SignerResponse, error) {
	// todo: generate script to set system time from command time data in command.content1
	return &datastructures.SignerResponse{
		Version: command.Version, Action: command.Action,
		Content1: "", Content2: "", Content3: ""}, nil
}

// Receive a request and generate a request data structure
func Receive(port *serial.Port, commandChan *chan datastructures.SignerRequest, errorChan *chan error) {
	header, err := shared.ReceiveBytes(port, 1, 20)
	if err != nil {
		*errorChan <- err
		return
	}
	if header[0] != shared.HandshakeByte {
		*errorChan <- fmt.Errorf("unexpected byte 0x%x expected 0x%x", header[0], shared.HandshakeByte)
	}

	if _, err := (*port).Write([]byte{shared.AckByte}); err != nil {
		*errorChan <- errors.New("could not write ACK")
		return
	}

	lengthBytes, err := shared.ReceiveBytes(port, 3, 2)
	if err != nil {
		*errorChan <- err
		return
	}
	blockLength := datastructures.Decode24BitLength(lengthBytes)
	blockData, err := shared.ReceiveBytes(port, blockLength, 5)
	if err != nil {
		*errorChan <- err
		return
	}

	checkSum, err := shared.ReceiveBytes(port, 1, 2)
	if err != nil {
		*errorChan <- err
		return
	}

	command, err := datastructures.SignerRequestFromData(lengthBytes, blockData, checkSum[0])
	if err != nil {
		*errorChan <- err
	}

	trailer, err := shared.ReceiveBytes(port, len(shared.MagicTrailer), 2)
	if err != nil {
		*errorChan <- err
		return
	}
	if string(trailer) != shared.MagicTrailer {
		*errorChan <- errors.New("expected trailer bytes not found")
		return
	}

	if _, err := (*port).Write([]byte{0x10}); err != nil {
		*errorChan <- err
		return
	}

	*commandChan <- *command
}