Add support for IOBuf::takeOwnership sizedFree

Summary:
Add support for IOBuf::takeOwnership sizedFree

(Note: this ignores all push blocking failures!)

Reviewed By: simpkins

Differential Revision: D28510736

fbshipit-source-id: b102bd462df3d85856897d4acfff689d371ceb6c

folly/io/IOBuf.cpp

@@ -377,6 +377,11 @@ IOBuf::IOBuf(
   // since we use that for folly::sizedFree
   DCHECK(!userData || (userData && freeFn));
 
+  // add support for sized dealloc if freeFn is null
+  if (!userData && !freeFn) {
+    userData = reinterpret_cast<void*>(capacity);
+  }
+
   auto rollback = makeGuard([&] { //
     takeOwnershipError(freeOnError, buf, freeFn, userData);
   });
@@ -396,6 +401,11 @@ unique_ptr<IOBuf> IOBuf::takeOwnership(
   // since we use that for folly::sizedFree
   DCHECK(!userData || (userData && freeFn));
 
+  // add support for sized dealloc if freeFn is null
+  if (!userData && !freeFn) {
+    userData = reinterpret_cast<void*>(capacity);
+  }
+
   HeapFullStorage* storage = nullptr;
   auto rollback = makeGuard([&] {
     if (storage) {