From 833eb660fd274164568a06d208fabd35e9dde9d5 Mon Sep 17 00:00:00 2001
From: Peter Hellberg <peter@c7.se>
Date: Tue, 5 Sep 2023 18:37:43 +0200
Subject: [PATCH] Check that the alphabet does not contain multibyte characters

---
 alphabet_test.go | 10 ++++++++++
 sqids.go         | 19 ++++++++++++++++---
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/alphabet_test.go b/alphabet_test.go
index f1472ad..6c7c907 100644
--- a/alphabet_test.go
+++ b/alphabet_test.go
@@ -5,6 +5,16 @@ import (
 	"testing"
 )
 
+func TestMultibyteAlphabet(t *testing.T) {
+	_, err := New(Options{
+		Alphabet: "ë1092",
+	})
+
+	if err != errAlphabetMultibyte {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}
+
 func TestAlphabetSimple(t *testing.T) {
 	numbers := []uint64{1, 2, 3}
 	id := "4d9fd2"
diff --git a/sqids.go b/sqids.go
index 7658f9a..707a4e6 100644
--- a/sqids.go
+++ b/sqids.go
@@ -18,6 +18,14 @@ const (
 
 var defaultBlocklist []string = newDefaultBlocklist()
 
+// Alphabet validation errors
+var (
+	errAlphabetMultibyte      = errors.New("alphabet must not contain any multibyte characters")
+	errAlphabetTooShort       = errors.New("alphabet length must be at least 5")
+	errAlphabetNotUniqueChars = errors.New("alphabet must contain unique characters")
+	errAlphabetMinLength      = errors.New("alphabet minimum length")
+)
+
 // Options for a custom instance of Sqids
 type Options struct {
 	Alphabet  string
@@ -59,19 +67,24 @@ func validatedOptions(o Options) (Options, error) {
 		o.Alphabet = defaultAlphabet
 	}
 
+	// check that the alphabet does not contain multibyte characters
+	if len(o.Alphabet) != len([]rune(o.Alphabet)) {
+		return Options{}, errAlphabetMultibyte
+	}
+
 	// check the length of the alphabet
 	if len(o.Alphabet) < minAlphabetLength {
-		return Options{}, errors.New("alphabet length must be at least 5")
+		return Options{}, errAlphabetTooShort
 	}
 
 	// check that the alphabet has only unique characters
 	if !hasUniqueChars(o.Alphabet) {
-		return Options{}, errors.New("alphabet must contain unique characters")
+		return Options{}, errAlphabetNotUniqueChars
 	}
 
 	// test min length (type [might be lang-specific] + min length + max length)
 	if o.MinLength < int(minUint64Value) || o.MinLength > len(o.Alphabet) {
-		return Options{}, fmt.Errorf("minimum length has to be between %d and %d", minUint64Value, len(o.Alphabet))
+		return Options{}, fmt.Errorf("%w has to be between %d and %d", errAlphabetMinLength, minUint64Value, len(o.Alphabet))
 	}
 
 	o.Blocklist = filterBlocklist(o.Alphabet, o.Blocklist)