feat: allow providing a custom --maxbytes param for a relay server

making the MAXBYTES customizable helps to run relay servers
which can allow an arbitary amount of max bytes. By default, the
MaxBytes will be set to 40000.

To set a custom MaxBytes variable value:

croc relay --maxbytes 10000000

src/cli/cli.go

@@ -80,6 +80,7 @@ func Run() (err error) {
 			Flags: []cli.Flag{
 				&cli.StringFlag{Name: "host", Usage: "host of the relay"},
 				&cli.StringFlag{Name: "ports", Value: "9009,9010,9011,9012,9013", Usage: "ports of the relay"},
+				&cli.IntFlag{Name: "maxbytes", Value: comm.MaxBytes, Usage: "maximum bytes which can be relayed"},
 			},
 		},
 	}
@@ -463,6 +464,8 @@ func relay(c *cli.Context) (err error) {
 		debugString = "debug"
 	}
 	host := c.String("host")
+	comm.MaxBytes = c.Int("maxbytes")
+	log.Debugf("setting the maxbytes allowed for relay as %d", comm.MaxBytes)
 	ports := strings.Split(c.String("ports"), ",")
 	tcpPorts := strings.Join(ports[1:], ",")
 	for i, port := range ports {

src/comm/comm.go

@@ -18,6 +18,7 @@ import (
 var Socks5Proxy = ""
 
 var MAGIC_BYTES = []byte("croc")
+var MaxBytes = 4000000
 
 // Comm is some basic TCP communication
 type Comm struct {
@@ -150,6 +151,11 @@ func (c *Comm) Read() (buf []byte, numBytes int, bs []byte, err error) {
 		return
 	}
 	numBytes = int(numBytesUint32)
+	if numBytes > MaxBytes {
+		err = fmt.Errorf("too many bytes: %d", numBytes)
+		log.Debug(err)
+		return
+	}
 
 	// shorten the reading deadline in case getting weird data
 	if err := c.connection.SetReadDeadline(time.Now().Add(10 * time.Second)); err != nil {

src/comm/comm_test.go

@@ -11,7 +11,7 @@ import (
 )
 
 func TestComm(t *testing.T) {
-	token := make([]byte, 3000)
+	token := make([]byte, MaxBytes)
 	if _, err := rand.Read(token); err != nil {
 		t.Error(err)
 	}