string_bytes: strip padding from base64 strings

Because of variations in different base64 implementation, it's been
decided to strip all padding from the end of a base64 string and
calculate its size from that.

src/string_bytes.cc

@@ -63,16 +63,15 @@ static inline size_t base64_decoded_size_fast(size_t size) {
 }
 
 static inline size_t base64_decoded_size(const char* src, size_t size) {
-  size = base64_decoded_size_fast(size);
+  if (size == 0)
+    return 0;
 
-  const char* end = src + size;
-  // check for trailing padding (1 or 2 bytes)
-  if (size > 0) {
-    if (end[-1] == '=') size--;
-    if (size > 0 && end[-2] == '=') size--;
-  }
+  if (src[size - 1] == '=')
+    size--;
+  if (size > 0 && src[size - 1] == '=')
+    size--;
 
-  return size;
+  return base64_decoded_size_fast(size);
 }
 
 

test/simple/test-buffer.js

@@ -980,6 +980,10 @@ assert.throws(function() {
   }
 })();
 
+// Make sure byteLength properly checks for base64 padding
+assert.equal(Buffer.byteLength('aaa=', 'base64'), 2);
+assert.equal(Buffer.byteLength('aaaa==', 'base64'), 3);
+
 // Regression test for #5482: should throw but not assert in C++ land.
 assert.throws(function() {
   Buffer('', 'buffer');