Add crypto.randomBytes (#922)

js/modules/k6/crypto/crypto.go

@@ -24,6 +24,7 @@ import (
 	"context"
 	"crypto/hmac"
 	"crypto/md5"
+	"crypto/rand"
 	"crypto/sha1"
 	"crypto/sha256"
 	"crypto/sha512"
@@ -50,6 +51,18 @@ func New() *Crypto {
 	return &Crypto{}
 }
 
+func (*Crypto) RandomBytes(ctx context.Context, size int) []byte {
+	if size < 1 {
+		common.Throw(common.GetRuntime(ctx), errors.New("Invalid size"))
+	}
+	bytes := make([]byte, size)
+	_, err := rand.Read(bytes)
+	if err != nil {
+		common.Throw(common.GetRuntime(ctx), err)
+	}
+	return bytes
+}
+
 func (c *Crypto) Md4(ctx context.Context, input []byte, outputEncoding string) string {
 	hasher := c.CreateHash(ctx, "md4")
 	hasher.Update(input)

js/modules/k6/crypto/crypto_test.go

@@ -22,6 +22,8 @@ package crypto
 
 import (
 	"context"
+	"crypto/rand"
+	"errors"
 	"testing"
 
 	"github.com/dop251/goja"
@@ -30,6 +32,12 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+type MockReader struct{}
+
+func (MockReader) Read(p []byte) (n int, err error) {
+	return -1, errors.New("Contrived failure")
+}
+
 func TestCryptoAlgorithms(t *testing.T) {
 	if testing.Short() {
 		return
@@ -41,6 +49,33 @@ func TestCryptoAlgorithms(t *testing.T) {
 	ctx = common.WithRuntime(ctx, rt)
 	rt.Set("crypto", common.Bind(rt, New(), &ctx))
 
+	t.Run("RandomBytesSuccess", func(t *testing.T) {
+		_, err := common.RunString(rt, `
+		let bytes = crypto.randomBytes(5);
+		if (bytes.length !== 5) {
+			throw new Error("Incorrect size: " + bytes.length);
+		}`)
+
+		assert.NoError(t, err)
+	})
+
+	t.Run("RandomBytesInvalidSize", func(t *testing.T) {
+		_, err := common.RunString(rt, `
+		crypto.randomBytes(-1);`)
+
+		assert.Error(t, err)
+	})
+
+	t.Run("RandomBytesFailure", func(t *testing.T) {
+		SavedReader := rand.Reader
+		rand.Reader = MockReader{}
+		_, err := common.RunString(rt, `
+		crypto.randomBytes(5);`)
+		rand.Reader = SavedReader
+
+		assert.Error(t, err)
+	})
+
 	t.Run("MD4", func(t *testing.T) {
 		_, err := common.RunString(rt, `
 		const correct = "aa010fbc1d14c795d86ef98c95479d17";