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nodejs · Oct 8, 2022 · 08dfdac · 08dfdac
1 parent c43f223
commit 08dfdac
Showing 1 changed file with 13 additions and 22 deletions.
diff --git a/lib/buffer.js b/lib/buffer.js
@@ -1256,6 +1256,8 @@ const kForgivingBase64AllowedChars = [
   0x2F, // /
   0x3D, // =
 ];
+const kEqualSignIndex = ArrayPrototypeIndexOf(kForgivingBase64AllowedChars,
+                                              0x3D);
 
 function atob(input) {
   // The implementation here has not been performance optimized in any way and
@@ -1266,7 +1268,6 @@ function atob(input) {
   }
 
   input = `${input}`;
-  const initLength = input.length;
   let nonAsciiWhitespaceCharCount = 0;
   let equalCharCount = 0;
 
@@ -1280,10 +1281,14 @@ function atob(input) {
       // ASCII whitespace char codes.
       nonAsciiWhitespaceCharCount++;
 
-      if (index === kForgivingBase64AllowedChars.length - 1 && equalCharCount !== 2) {
-        // The last element of `kForgivingBase64AllowedChars` is the `=`
+      if (index === kEqualSignIndex) {
         equalCharCount++;
       } else if (equalCharCount) {
+        // The `=` char is only allowed at the end.
+        throw lazyDOMException('Invalid character', 'InvalidCharacterError');
+      }
+
+      if (equalCharCount > 2) {
         // Only one more `=` is permitted after the first equal sign.
         throw lazyDOMException('Invalid character', 'InvalidCharacterError');
       }
@@ -1292,28 +1297,14 @@ function atob(input) {
     }
   }
 
-  // See #2 and #4 - https://infra.spec.whatwg.org/#forgiving-base64
-  if (equalCharCount > 2) {
-    throw lazyDOMException('Invalid character', 'InvalidCharacterError');
-  }
-
   let reminder = nonAsciiWhitespaceCharCount % 4;
 
-  // See #2 - https://infra.spec.whatwg.org/#forgiving-base64
+  // See #2, #3, #4 - https://infra.spec.whatwg.org/#forgiving-base64
   if (!reminder) {
-    // Remove all trailing `=` characters (whitespace characters will be
-    // ignored).
-    input = input.replace(/(=\s*){1,2}$/, (s) => {
-      return s.replace(/=/gi, '');
-    });
-    const deltaLength = initLength - input.length;
-    nonAsciiWhitespaceCharCount -= deltaLength;
-    equalCharCount -= deltaLength;
-    reminder = nonAsciiWhitespaceCharCount % 4;
-  }
-
-  // See #4 - https://infra.spec.whatwg.org/#forgiving-base64
-  if (equalCharCount) {
+    // Remove all trailing `=` characters and get the new reminder.
+    reminder = (nonAsciiWhitespaceCharCount - equalCharCount) % 4;
+  } else if (equalCharCount) {
+    // `=` should not in the input if there's a reminder.
     throw lazyDOMException('Invalid character', 'InvalidCharacterError');
   }