src: use offset calc. instead of req->data in node_file

A small refactor – this removes one layer of pointer indirection.
(The performance gain is likely negligible, the main point here
being that this encapsulates libuv request management a bit more.)

PR-URL: #21839
Reviewed-By: Eugene Ostroukhov <eostroukhov@google.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Jon Moss <me@jonathanmoss.me>

Author: addaleax

src/node_file.cc

@@ -221,7 +221,7 @@ inline MaybeLocal<Promise> FileHandle::ClosePromise() {
     closing_ = true;
     CloseReq* req = new CloseReq(env(), promise, object());
     auto AfterClose = uv_fs_callback_t{[](uv_fs_t* req) {
-      CloseReq* close = static_cast<CloseReq*>(req->data);
+      CloseReq* close = CloseReq::from_req(req);
       CHECK_NOT_NULL(close);
       close->file_handle()->AfterClose();
       Isolate* isolate = close->env()->isolate();
@@ -475,15 +475,15 @@ bool FSReqAfterScope::Proceed() {
 }
 
 void AfterNoArgs(uv_fs_t* req) {
-  FSReqBase* req_wrap = static_cast<FSReqBase*>(req->data);
+  FSReqBase* req_wrap = FSReqBase::from_req(req);
   FSReqAfterScope after(req_wrap, req);
 
   if (after.Proceed())
     req_wrap->Resolve(Undefined(req_wrap->env()->isolate()));
 }
 
 void AfterStat(uv_fs_t* req) {
-  FSReqBase* req_wrap = static_cast<FSReqBase*>(req->data);
+  FSReqBase* req_wrap = FSReqBase::from_req(req);
   FSReqAfterScope after(req_wrap, req);
 
   if (after.Proceed()) {
@@ -492,15 +492,15 @@ void AfterStat(uv_fs_t* req) {
 }
 
 void AfterInteger(uv_fs_t* req) {
-  FSReqBase* req_wrap = static_cast<FSReqBase*>(req->data);
+  FSReqBase* req_wrap = FSReqBase::from_req(req);
   FSReqAfterScope after(req_wrap, req);
 
   if (after.Proceed())
     req_wrap->Resolve(Integer::New(req_wrap->env()->isolate(), req->result));
 }
 
 void AfterOpenFileHandle(uv_fs_t* req) {
-  FSReqWrap* req_wrap = static_cast<FSReqWrap*>(req->data);
+  FSReqBase* req_wrap = FSReqBase::from_req(req);
   FSReqAfterScope after(req_wrap, req);
 
   if (after.Proceed()) {
@@ -510,7 +510,7 @@ void AfterOpenFileHandle(uv_fs_t* req) {
 }
 
 void AfterStringPath(uv_fs_t* req) {
-  FSReqBase* req_wrap = static_cast<FSReqBase*>(req->data);
+  FSReqBase* req_wrap = FSReqBase::from_req(req);
   FSReqAfterScope after(req_wrap, req);
 
   MaybeLocal<Value> link;
@@ -529,7 +529,7 @@ void AfterStringPath(uv_fs_t* req) {
 }
 
 void AfterStringPtr(uv_fs_t* req) {
-  FSReqBase* req_wrap = static_cast<FSReqBase*>(req->data);
+  FSReqBase* req_wrap = FSReqBase::from_req(req);
   FSReqAfterScope after(req_wrap, req);
 
   MaybeLocal<Value> link;
@@ -548,7 +548,7 @@ void AfterStringPtr(uv_fs_t* req) {
 }
 
 void AfterScanDir(uv_fs_t* req) {
-  FSReqBase* req_wrap = static_cast<FSReqBase*>(req->data);
+  FSReqBase* req_wrap = FSReqBase::from_req(req);
   FSReqAfterScope after(req_wrap, req);
 
   if (after.Proceed()) {

src/node_file.h

@@ -68,6 +68,10 @@ class FSReqBase : public ReqWrap<uv_fs_t> {
 
   bool use_bigint() const { return use_bigint_; }
 
+  static FSReqBase* from_req(uv_fs_t* req) {
+    return static_cast<FSReqBase*>(ReqWrap::from_req(req));
+  }
+
  private:
   enum encoding encoding_ = UTF8;
   bool has_data_ = false;
@@ -284,6 +288,10 @@ class FileHandle : public AsyncWrap, public StreamBase {
 
     void Reject(Local<Value> reason);
 
+    static CloseReq* from_req(uv_fs_t* req) {
+      return static_cast<CloseReq*>(ReqWrap::from_req(req));
+    }
+
    private:
     Persistent<Promise> promise_;
     Persistent<Value> ref_;