Add random string generation capabilities

random/random.go

@@ -0,0 +1,46 @@
+// Package random provides utilities and functions for generating random data.
+package random
+
+import (
+	"bytes"
+	"crypto/rand"
+	"math/big"
+)
+
+// Character sets that you can use when passing into RandomString
+const Digits = "0123456789"
+const UpperLetters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+const LowerLetters = "abcdefghijklmnopqrstuvwxyz"
+const SpecialChars = "<>[]{}()-_*%&/?\"'\\"
+
+var Base62Chars = Digits + UpperLetters + LowerLetters
+
+// RandomString generates a random string of length strLength, composing only of characters in allowedChars. Based on
+// code here: http://stackoverflow.com/a/9543797/483528
+// For convenience, the random package exposes various character sets you can use for the allowedChars parameter. Here
+// are a few examples:
+//
+// // Only lower case chars + digits
+// random.RandomString(6, random.Digits + random.LowerLetters)
+//
+// // alphanumerics + special chars
+// random.RandomString(6, random.Base62Chars + random.SpecialChars)
+//
+// // Only alphanumerics (base62)
+// random.RandomString(6, random.Base62Chars)
+//
+// // Only abc
+// random.RandomString(6, "abc")
+func RandomString(strLength int, allowedChars string) (string, error) {
+	var out bytes.Buffer
+
+	for i := 0; i < strLength; i++ {
+		id, err := rand.Int(rand.Reader, big.NewInt(int64(len(allowedChars))))
+		if err != nil {
+			return out.String(), err
+		}
+		out.WriteByte(allowedChars[id.Int64()])
+	}
+
+	return out.String(), nil
+}

random/random_test.go

@@ -0,0 +1,46 @@
+package random
+
+import (
+	"strconv"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestRandomStringIsMostlyRandom(t *testing.T) {
+	t.Parallel()
+
+	// Ensure that there is no overlap in 32 character random strings generated 100 times
+	seen := map[string]bool{}
+	for i := 0; i < 100; i++ {
+		newStr, err := RandomString(32, Base62Chars)
+		require.NoError(t, err)
+		_, hasSeen := seen[newStr]
+		require.False(t, hasSeen)
+		seen[newStr] = true
+	}
+}
+
+func TestRandomStringRespectsStrLen(t *testing.T) {
+	t.Parallel()
+
+	for i := 0; i < 40; i++ {
+		newStr, err := RandomString(i, Base62Chars)
+		require.NoError(t, err)
+		assert.Equal(t, len(newStr), i)
+	}
+}
+
+func TestRandomStringRespectsAllowedChars(t *testing.T) {
+	t.Parallel()
+
+	for i := 0; i < 100; i++ {
+		newStr, err := RandomString(10, Digits)
+		require.NoError(t, err)
+		// Since the new string should only be composed of digits, if RandomString respects allowed chars you should
+		// always be able to convert the string to an int
+		_, err = strconv.Atoi(newStr)
+		require.NoError(t, err)
+	}
+}