perf(ext/web): avoid reallocations in op_base64_atob (#15018)

ext/web/lib.rs

@@ -124,25 +124,27 @@ pub fn init<P: TimersPermission + 'static>(
 
 #[op]
 fn op_base64_decode(input: String) -> Result<ZeroCopyBuf, AnyError> {
-  Ok(forgiving_base64_decode(input.into_bytes())?.into())
+  let mut s = input.into_bytes();
+  let decoded_len = forgiving_base64_decode(&mut s)?;
+  s.truncate(decoded_len);
+  Ok(s.into())
 }
 
 #[op]
-fn op_base64_atob(s: ByteString) -> Result<ByteString, AnyError> {
-  Ok(forgiving_base64_decode(s.into())?.into())
+fn op_base64_atob(mut s: ByteString) -> Result<ByteString, AnyError> {
+  let decoded_len = forgiving_base64_decode(&mut s)?;
+  s.truncate(decoded_len);
+  Ok(s)
 }
 
 /// See <https://infra.spec.whatwg.org/#forgiving-base64>
-fn forgiving_base64_decode(mut input: Vec<u8>) -> Result<Vec<u8>, AnyError> {
+#[inline]
+fn forgiving_base64_decode(input: &mut [u8]) -> Result<usize, AnyError> {
   let error: _ =
     || DomExceptionInvalidCharacterError::new("Failed to decode base64");
-
-  let decoded = base64_simd::Base64::forgiving_decode_inplace(&mut input)
+  let decoded = base64_simd::Base64::forgiving_decode_inplace(input)
     .map_err(|_| error())?;
-
-  let decoded_len = decoded.len();
-  input.truncate(decoded_len);
-  Ok(input)
+  Ok(decoded.len())
 }
 
 #[op]
@@ -156,9 +158,10 @@ fn op_base64_btoa(s: ByteString) -> String {
 }
 
 /// See <https://infra.spec.whatwg.org/#forgiving-base64>
+#[inline]
 fn forgiving_base64_encode(s: &[u8]) -> String {
-  let base64 = base64_simd::Base64::STANDARD;
-  base64.encode_to_boxed_str(s).into_string()
+  const BASE64_STANDARD: base64_simd::Base64 = base64_simd::Base64::STANDARD;
+  BASE64_STANDARD.encode_to_boxed_str(s).into_string()
 }
 
 #[derive(Deserialize)]