Use global, sync'ed random source

Almost unbelievably it appears tests on AppVeyor get the same value when
seeding the random generator. See https://ci.appveyor.com/project/otoolep/rqlite/builds/47853399

db/db.go

@@ -1405,18 +1405,6 @@ func isTextType(t string) bool {
 		strings.HasPrefix(t, "clob")
 }
 
-func randomString() string {
-	var output strings.Builder
-	chars := "abcdedfghijklmnopqrstABCDEFGHIJKLMNOP"
-
-	for i := 0; i < 20; i++ {
-		random := rand.Intn(len(chars))
-		randomChar := chars[random]
-		output.WriteByte(randomChar)
-	}
-	return output.String()
-}
-
 func containsEmptyType(slice []string) bool {
 	for _, str := range slice {
 		if str == "" {

random/random.go

@@ -0,0 +1,29 @@
+package random
+
+import (
+	"math/rand"
+	"strings"
+	"sync"
+	"time"
+)
+
+var r *rand.Rand
+var mu sync.Mutex
+
+func init() {
+	r = rand.New(rand.NewSource(time.Now().UnixNano()))
+}
+
+// RandomString returns a random string of 20 characters
+func RandomString() string {
+	mu.Lock()
+	defer mu.Unlock()
+	var output strings.Builder
+	chars := "abcdedfghijklmnopqrstABCDEFGHIJKLMNOP"
+	for i := 0; i < 20; i++ {
+		random := r.Intn(len(chars))
+		randomChar := chars[random]
+		output.WriteString(string(randomChar))
+	}
+	return output.String()
+}

random/random_test.go

@@ -0,0 +1,25 @@
+package random
+
+import (
+	"testing"
+)
+
+func Test_RandomStringLength(t *testing.T) {
+	str := RandomString()
+	if len(str) != 20 {
+		t.Errorf("RandomString() returned a string of length %d; want 20", len(str))
+	}
+}
+
+func Test_RandomStringUniqueness(t *testing.T) {
+	const numStrings = 100
+	strs := make(map[string]bool, numStrings)
+
+	for i := 0; i < numStrings; i++ {
+		str := RandomString()
+		if strs[str] {
+			t.Errorf("RandomString() returned a non-unique string: %s", str)
+		}
+		strs[str] = true
+	}
+}

store/store_test.go

@@ -5,18 +5,17 @@ import (
 	"errors"
 	"expvar"
 	"fmt"
-	"math/rand"
 	"net"
 	"os"
 	"path/filepath"
 	"sort"
-	"strings"
 	"testing"
 	"time"
 
 	"github.com/rqlite/rqlite/command"
 	"github.com/rqlite/rqlite/command/encoding"
 	"github.com/rqlite/rqlite/db"
+	"github.com/rqlite/rqlite/random"
 	"github.com/rqlite/rqlite/testdata/chinook"
 )
 
@@ -2867,18 +2866,18 @@ func mustNewStoreAtPathsLn(id, dataPath, sqlitePath string, fk bool) (*Store, ne
 }
 
 func mustNewStore(t *testing.T) (*Store, net.Listener) {
-	return mustNewStoreAtPathsLn(randomString(), t.TempDir(), "", false)
+	return mustNewStoreAtPathsLn(random.RandomString(), t.TempDir(), "", false)
 }
 
 func mustNewStoreFK(t *testing.T) (*Store, net.Listener) {
-	return mustNewStoreAtPathsLn(randomString(), t.TempDir(), "", true)
+	return mustNewStoreAtPathsLn(random.RandomString(), t.TempDir(), "", true)
 }
 
 func mustNewStoreSQLitePath(t *testing.T) (*Store, net.Listener, string) {
 	dataDir := t.TempDir()
 	sqliteDir := t.TempDir()
 	sqlitePath := filepath.Join(sqliteDir, "explicit-path.db")
-	s, ln := mustNewStoreAtPathsLn(randomString(), dataDir, sqlitePath, true)
+	s, ln := mustNewStoreAtPathsLn(random.RandomString(), dataDir, sqlitePath, true)
 	return s, ln, sqlitePath
 }
 
@@ -3103,19 +3102,6 @@ func asJSONAssociative(v interface{}) string {
 	return string(b)
 }
 
-func randomString() string {
-	var output strings.Builder
-	r := rand.New(rand.NewSource(time.Now().UnixNano()))
-	chars := "abcdedfghijklmnopqrstABCDEFGHIJKLMNOP"
-
-	for i := 0; i < 20; i++ {
-		random := r.Intn(len(chars))
-		randomChar := chars[random]
-		output.WriteString(string(randomChar))
-	}
-	return output.String()
-}
-
 func testPoll(t *testing.T, f func() bool, p time.Duration, d time.Duration) {
 	tck := time.NewTicker(p)
 	defer tck.Stop()