buffer: speed up concat via TypedArray#set

Author: gurgunday

lib/buffer.js

@@ -51,6 +51,7 @@ const {
   TypedArrayPrototypeGetLength,
   TypedArrayPrototypeSet,
   TypedArrayPrototypeSlice,
+  TypedArrayPrototypeSubarray,
   Uint8Array,
 } = primordials;
 
@@ -600,7 +601,21 @@ Buffer.concat = function concat(list, length) {
       throw new ERR_INVALID_ARG_TYPE(
         `list[${i}]`, ['Buffer', 'Uint8Array'], list[i]);
     }
-    pos += _copyActual(buf, buffer, pos, 0, buf.length);
+
+    if (buf.length === 0 || pos >= length) {
+      // Empty buf or destination is full; subsequent copies are no-ops.
+      // We don't break to preserve compatibility and throw if isUint8Array fails.
+      continue;
+    }
+
+    const available = length - pos;
+    const toCopy = buf.length > available ? available : buf.length;
+    if (toCopy === buf.length) {
+      TypedArrayPrototypeSet(buffer, buf, pos);
+    } else {
+      TypedArrayPrototypeSet(buffer, TypedArrayPrototypeSubarray(buf, 0, toCopy), pos);
+    }
+    pos += toCopy;
   }
 
   // Note: `length` is always equal to `buffer.length` at this point