Use crypto/rand to generate random numbers

cmd/bgammon-server/game.go

@@ -3,7 +3,6 @@ package main
 import (
 	"bufio"
 	"bytes"
-	"math/rand"
 	"time"
 
 	"code.rocket9labs.com/tslocum/bgammon"
@@ -22,7 +21,6 @@ type serverGame struct {
 	rematch    int
 	rejoin1    bool
 	rejoin2    bool
-	r          *rand.Rand
 	*bgammon.Game
 }
 
@@ -33,7 +31,6 @@ func newServerGame(id int) *serverGame {
 		created:    now,
 		lastActive: now,
 		Game:       bgammon.NewGame(),
-		r:          rand.New(rand.NewSource(time.Now().UnixNano() + rand.Int63n(1000000))),
 	}
 }
 
@@ -50,14 +47,14 @@ func (g *serverGame) roll(player int) bool {
 			} else {
 				secondRoll = true
 			}
-			g.Roll1 = g.r.Intn(6) + 1
+			g.Roll1 = randInt(6) + 1
 		} else {
 			if g.Roll2 != 0 {
 				return false
 			} else {
 				secondRoll = true
 			}
-			g.Roll2 = g.r.Intn(6) + 1
+			g.Roll2 = randInt(6) + 1
 		}
 		if secondRoll && g.Started.IsZero() {
 			g.Started = time.Now()
@@ -72,7 +69,8 @@ func (g *serverGame) roll(player int) bool {
 		return false
 	}
 
-	g.Roll1, g.Roll2 = g.r.Intn(6)+1, g.r.Intn(6)+1
+	g.Roll1 = randInt(6) + 1
+	g.Roll2 = randInt(6) + 1
 	return true
 }
 
@@ -184,8 +182,7 @@ func (g *serverGame) addClient(client *serverClient) (bool, string) {
 		client.playerNumber = 1
 		playerNumber = 1
 	default:
-		i := rand.Intn(2)
-		if i == 0 {
+		if randInt(2) == 0 {
 			g.client1 = client
 			g.Player1.Name = string(client.name)
 			client.playerNumber = 1

cmd/bgammon-server/main.go

@@ -10,15 +10,22 @@ import (
 
 func main() {
 	var (
-		tcpAddress string
-		wsAddress  string
-		debug      int
+		tcpAddress     string
+		wsAddress      string
+		debug          int
+		rollStatistics bool
 	)
 	flag.StringVar(&tcpAddress, "tcp", "localhost:1337", "TCP listen address")
 	flag.StringVar(&wsAddress, "ws", "localhost:1338", "WebSocket listen address")
 	flag.IntVar(&debug, "debug", 0, "print debug information and serve pprof on specified port")
+	flag.BoolVar(&rollStatistics, "statistics", false, "print dice roll statistics and exit")
 	flag.Parse()
 
+	if rollStatistics {
+		printRollStatistics()
+		return
+	}
+
 	if tcpAddress == "" && wsAddress == "" {
 		log.Fatal("Error: A TCP and/or WebSocket listen address must be specified.")
 	}
@@ -38,3 +45,26 @@ func main() {
 	}
 	select {}
 }
+
+func printRollStatistics() {
+	var oneSame, doubles int
+	var lastroll1, lastroll2 int
+
+	total := 1000000
+	for i := 0; i < total; i++ {
+		roll1 := randInt(6) + 1
+		roll2 := randInt(6) + 1
+
+		if roll1 == lastroll1 || roll1 == lastroll2 || roll2 == lastroll1 || roll2 == lastroll2 {
+			oneSame++
+		}
+
+		if roll1 == roll2 {
+			doubles++
+		}
+
+		lastroll1, lastroll2 = roll1, roll2
+	}
+
+	log.Printf("total: %d, one same: %d (%.0f%%), doubles: %d (%.0f%%)", total, oneSame, float64(oneSame)/float64(total)*100, doubles, float64(doubles)/float64(total)*100)
+}

cmd/bgammon-server/server.go

@@ -2,9 +2,10 @@ package main
 
 import (
 	"bytes"
+	"crypto/rand"
 	"fmt"
 	"log"
-	"math/rand"
+	"math/big"
 	"net"
 	"net/http"
 	"regexp"
@@ -18,7 +19,7 @@ import (
 
 const clientTimeout = 40 * time.Second
 
-const allowDebugCommands = false
+var allowDebugCommands bool
 
 var (
 	onlyNumbers = regexp.MustCompile(`^[0-9]+$`)
@@ -262,8 +263,7 @@ func (s *server) handleNewClientIDs() {
 // randomUsername returns a random guest username, and assumes clients are already locked.
 func (s *server) randomUsername() []byte {
 	for {
-		i := 100 + rand.Intn(900)
-		name := []byte(fmt.Sprintf("Guest%d", i))
+		name := []byte(fmt.Sprintf("Guest%d", 100+randInt(900)))
 
 		if s.clientByUsername(name) == nil {
 			return name
@@ -1081,3 +1081,11 @@ COMMANDS:
 		}
 	}
 }
+
+func randInt(max int) int {
+	i, err := rand.Int(rand.Reader, big.NewInt(int64(max)))
+	if err != nil {
+		panic(err)
+	}
+	return int(i.Int64())
+}