internal: add randutil.String() helper

internal/randutil/randutil.go

@@ -0,0 +1,39 @@
+package randutil
+
+import (
+	"math/rand"
+)
+
+const (
+	AsciiLower  = "abcdefghijklmnopqrstuvwxyz"
+	AsciiUpper  = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+	AsciiDigit  = "0123456789"
+	AsciiSymbol = "!@#$%^&*()-_=+[]{}|;:',.<>/?`~"
+)
+
+// String returns a (weak) random string of the length "n". When not
+// passing a seqs it will generate the string based on ascii
+// lower,upper,digits and a bunch of (ascii) symbols.
+//
+// With seqs passed it will select based on the provided
+// sequences, i.e. String(10, AsciiDigits) will produce 10
+// random digits.
+//
+// Do not use to generate secrets.
+func String(n int, seqs ...string) string {
+	if len(seqs) == 0 {
+		seqs = []string{AsciiLower, AsciiUpper, AsciiDigit, AsciiSymbol}
+	}
+
+	var inp []byte
+	for _, s := range seqs {
+		inp = append(inp, []byte(s)...)
+	}
+
+	b := make([]byte, n)
+	for i := range b {
+		// nolint:gosec
+		b[i] = inp[rand.Intn(len(inp))]
+	}
+	return string(b)
+}

internal/randutil/randutil_test.go

@@ -0,0 +1,33 @@
+package randutil_test
+
+import (
+	"testing"
+	"unicode"
+
+	"github.com/stretchr/testify/assert"
+
+	"github.com/osbuild/images/internal/randutil"
+)
+
+func TestChoiceSimple(t *testing.T) {
+	n := 128
+
+	r1 := randutil.String(n)
+	r2 := randutil.String(n)
+	assert.NotEqual(t, r1, r2)
+	assert.Len(t, r1, n)
+	assert.Len(t, r2, n)
+	// by default we pick lower,upper,digit,symbols, ensure
+	// we do not stray from this range
+	defaultChars := randutil.AsciiLower + randutil.AsciiUpper + randutil.AsciiDigit + randutil.AsciiSymbol
+	for _, char := range r1 {
+		assert.Contains(t, []rune(defaultChars), char)
+	}
+}
+
+func TestChoiceHonorsSeq(t *testing.T) {
+	result := randutil.String(128, randutil.AsciiDigit)
+	for _, char := range result {
+		assert.True(t, unicode.IsDigit(char))
+	}
+}

pkg/distro/bootc/bootc_test.go

@@ -4,14 +4,14 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"math/rand"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
 
 	"github.com/osbuild/blueprint/pkg/blueprint"
 
 	"github.com/osbuild/images/internal/common"
+	"github.com/osbuild/images/internal/randutil"
 	"github.com/osbuild/images/pkg/container"
 	"github.com/osbuild/images/pkg/distro"
 	"github.com/osbuild/images/pkg/dnfjson"
@@ -54,19 +54,9 @@ func TestManifestGenerationEmptyConfig(t *testing.T) {
 	}
 }
 
-func randomLetters(n int) string {
-	const letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
-
-	b := make([]byte, n)
-	for i := range b {
-		b[i] = letters[rand.Intn(len(letters))]
-	}
-	return string(b)
-}
-
 func getUserConfig() *blueprint.Blueprint {
 	// add a user
-	pass := randomLetters(20)
+	pass := randutil.String(20)
 	key := "ssh-ed25519 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
 	return &blueprint.Blueprint{
 		Customizations: &blueprint.Customizations{