Correctly transform base64 with multiple instances of + or / (#4252)

String.replace only replaces a single instance of the search pattern by default; we need a regex in g mode if we want to replace them all.

spec/unit/base64.spec.ts

@@ -50,17 +50,18 @@ describe.each(["browser", "node"])("Base64 encoding (%s)", (env) => {
     });
 
     it("Should encode unpadded URL-safe base64", () => {
-        const toEncode = "?????";
+        // Chosen to have padding and multiple instances of / and + in the base64
+        const toEncode = "???????⊕⊗⊗";
         const data = new TextEncoder().encode(toEncode);
 
         const encoded = encodeUnpaddedBase64Url(data);
-        expect(encoded).toEqual("Pz8_Pz8");
+        expect(encoded).toEqual("Pz8_Pz8_P-KKleKKl-KKlw");
     });
 
     it("Should decode URL-safe base64", () => {
-        const decoded = new TextDecoder().decode(decodeBase64("Pz8_Pz8="));
+        const decoded = new TextDecoder().decode(decodeBase64("Pz8_Pz8_P-KKleKKl-KKlw=="));
 
-        expect(decoded).toStrictEqual("?????");
+        expect(decoded).toStrictEqual("???????⊕⊗⊗");
     });
 
     it("Encode unpadded should not have padding", () => {

src/base64.ts

@@ -59,7 +59,7 @@ export function encodeUnpaddedBase64(uint8Array: ArrayBuffer | Uint8Array): stri
  * @returns The unpadded base64.
  */
 export function encodeUnpaddedBase64Url(uint8Array: ArrayBuffer | Uint8Array): string {
-    return encodeUnpaddedBase64(uint8Array).replace("+", "-").replace("/", "_");
+    return encodeUnpaddedBase64(uint8Array).replace(/\+/g, "-").replace(/\//g, "_");
 }
 
 /**
@@ -75,7 +75,7 @@ export function decodeBase64(base64: string): Uint8Array {
         const itFunc = function* (): Generator<number> {
             const decoded = atob(
                 // built-in atob doesn't support base64url: convert so we support either
-                base64.replace("-", "+").replace("_", "/"),
+                base64.replace(/-/g, "+").replace(/_/g, "/"),
             );
             for (let i = 0; i < decoded.length; ++i) {
                 yield decoded.charCodeAt(i);