randutil: introduce an utility package for random value generation

randutil/crypto.go

@@ -0,0 +1,46 @@
+// -*- Mode: Go; indent-tabs-mode: t -*-
+
+/*
+ * Copyright (C) 2020 Canonical Ltd
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+package randutil
+
+import (
+	cryptorand "crypto/rand"
+	"encoding/base64"
+	"fmt"
+)
+
+// CryptoTokenBytes returns a crypthographically random token byte sequence.
+func CryptoTokenBytes(nbytes int) ([]byte, error) {
+	b := make([]byte, nbytes)
+	_, err := cryptorand.Read(b)
+	if err != nil {
+		return nil, fmt.Errorf("canot obtain %d crypto random bytes: %v", nbytes, err)
+	}
+	return b, nil
+}
+
+// CryptoToken returns a crypthographically random token string.
+// The result is URL-safe.
+func CryptoToken(nbytes int) (string, error) {
+	b, err := CryptoTokenBytes(nbytes)
+	if err != nil {
+		return "", err
+	}
+	return base64.RawURLEncoding.EncodeToString(b), nil
+}

randutil/crypto_test.go

@@ -0,0 +1,47 @@
+// -*- Mode: Go; indent-tabs-mode: t -*-
+
+/*
+ * Copyright (C) 2020 Canonical Ltd
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+package randutil_test
+
+import (
+	"encoding/base64"
+
+	. "gopkg.in/check.v1"
+
+	"github.com/snapcore/snapd/randutil"
+)
+
+type cryptoRandutilSuite struct{}
+
+var _ = Suite(&cryptoRandutilSuite{})
+
+func (s *cryptoRandutilSuite) TestCryptoTokenBytes(c *C) {
+	x, err := randutil.CryptoTokenBytes(5)
+	c.Assert(err, IsNil)
+	c.Check(x, HasLen, 5)
+}
+
+func (s *cryptoRandutilSuite) TestCryptoToken(c *C) {
+	x, err := randutil.CryptoToken(5)
+	c.Assert(err, IsNil)
+
+	b, err := base64.RawURLEncoding.DecodeString(x)
+	c.Assert(err, IsNil)
+	c.Check(b, HasLen, 5)
+}

randutil/rand.go

@@ -0,0 +1,63 @@
+// -*- Mode: Go; indent-tabs-mode: t -*-
+
+/*
+ * Copyright (C) 2014-2020 Canonical Ltd
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+// Package randutil initialises properly random value generation and
+// exposes a streamlined set of functions for it, including for crypto
+// random tokens.
+package randutil
+
+import (
+	cryptorand "crypto/rand"
+	"fmt"
+	"math"
+	"math/big"
+	"math/rand"
+)
+
+func init() {
+	// golang does not init Seed() itself
+	bigSeed, err := cryptorand.Int(cryptorand.Reader, big.NewInt(math.MaxInt64))
+	if err != nil {
+		panic(fmt.Sprintf("cannot obtain random seed: %v", err))
+	}
+	rand.Seed(bigSeed.Int64())
+}
+
+const letters = "BCDFGHJKLMNPQRSTVWXYbcdfghjklmnpqrstvwxy0123456789"
+
+// MakeRandomString returns a random string of length length
+//
+// The vowels are omitted to avoid that words are created by pure
+// chance. Numbers are included.
+//
+// Not cryptographically safe.
+func MakeRandomString(length int) string {
+	out := ""
+	for i := 0; i < length; i++ {
+		out += string(letters[rand.Intn(len(letters))])
+	}
+
+	return out
+}
+
+// Rexported from math/rand for streamlining.
+var (
+	Intn   = rand.Intn
+	Int63n = rand.Int63n
+)

randutil/rand_test.go

@@ -0,0 +1,46 @@
+// -*- Mode: Go; indent-tabs-mode: t -*-
+
+/*
+ * Copyright (C) 2014-2020 Canonical Ltd
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+package randutil_test
+
+import (
+	"math/rand"
+	"testing"
+
+	. "gopkg.in/check.v1"
+
+	"github.com/snapcore/snapd/randutil"
+)
+
+func Test(t *testing.T) { TestingT(t) }
+
+type randutilSuite struct{}
+
+var _ = Suite(&randutilSuite{})
+
+func (s *randutilSuite) TestMakeRandomString(c *C) {
+	// for our tests
+	rand.Seed(1)
+
+	s1 := randutil.MakeRandomString(10)
+	c.Assert(s1, Equals, "pw7MpXh0JB")
+
+	s2 := randutil.MakeRandomString(5)
+	c.Assert(s2, Equals, "4PQyl")
+}