fix utm unicode

src/app/[locale]/(payment)/payment/route.ts

@@ -3,8 +3,18 @@ import { NextRequest, NextResponse } from "next/server";
 import { createPaymentCheckout } from "@/entities/payment/api";
 import { ROUTES } from "@/shared/constants/client-routes";
 
+/**
+ * Convert base64 string to bytes (handles UTF-8 properly)
+ * MDN recommended approach: https://developer.mozilla.org/en-US/docs/Web/API/Window/btoa#unicode_strings
+ */
+function base64ToBytes(base64: string): Uint8Array {
+  const binString = atob(base64);
+  return Uint8Array.from(binString, (m) => m.codePointAt(0) ?? 0);
+}
+
 /**
  * Decode URL-safe base64 state parameter to UTM object
+ * Supports UTF-8 encoded content (e.g., utm_campaign=夏セール)
  */
 function decodeStateParam(state: string): Record<string, string> | undefined {
   if (!state) return undefined;
@@ -16,7 +26,9 @@ function decodeStateParam(state: string): Record<string, string> | undefined {
     while (base64.length % 4) {
       base64 += "=";
     }
-    const json = atob(base64);
+    // Decode base64 to bytes, then decode UTF-8
+    const bytes = base64ToBytes(base64);
+    const json = new TextDecoder().decode(bytes);
     return JSON.parse(json);
   } catch {
     return undefined;

src/shared/utils/url.ts

@@ -61,17 +61,30 @@ export const getCurrentQueryParams = (): Record<string, string> => {
   return utmParams;
 };
 
+/**
+ * Convert bytes to base64 string (handles UTF-8 properly)
+ * MDN recommended approach: https://developer.mozilla.org/en-US/docs/Web/API/Window/btoa#unicode_strings
+ */
+const bytesToBase64 = (bytes: Uint8Array): string => {
+  const binString = Array.from(bytes, (byte) =>
+    String.fromCodePoint(byte)
+  ).join("");
+  return btoa(binString);
+};
+
 /**
  * Encode params as base64 JSON for state parameter
- * Uses URL-safe base64 encoding
+ * Uses URL-safe base64 encoding with UTF-8 support
+ * Handles Unicode characters (e.g., utm_campaign=夏セール)
  */
 export const encodeStateParam = (params: Record<string, string>): string => {
   if (Object.keys(params).length === 0) return "";
 
   try {
     const json = JSON.stringify(params);
-    // Use btoa for base64, replace unsafe chars for URL
-    const base64 = btoa(json)
+    // Encode string as UTF-8 bytes, then convert to base64
+    const bytes = new TextEncoder().encode(json);
+    const base64 = bytesToBase64(bytes)
       .replace(/\+/g, "-")
       .replace(/\//g, "_")
       .replace(/=+$/, "");