fix an issue that calling Touch() right before file deletion causes use-after-free

main.cc

@@ -206,10 +206,11 @@ class Env final : public nf7::Env {
     }
   }
 
-  void Handle(const nf7::File::Event& e) noexcept override
+  nf7::File* Handle(const nf7::File::Event& e) noexcept override
   try {
     // trigger File::Handle()
-    GetFileOrThrow(e.id).Handle(e);
+    auto& f = GetFileOrThrow(e.id);
+    f.Handle(e);
 
     // trigger file watcher
     auto itr = watchers_map_.find(e.id);
@@ -219,7 +220,10 @@ class Env final : public nf7::Env {
 
     // trigger global watcher
     for (auto w : watchers_map_[0]) w->Handle(e);
+
+    return &f;
   } catch (nf7::ExpiredException&) {
+    return nullptr;
   }
 
   void Exit() noexcept override {

nf7.cc

@@ -105,11 +105,12 @@ void File::Touch() noexcept {
   if (std::exchange(touch_, true)) {
     return;
   }
-  env().ExecMain(std::make_shared<nf7::GenericContext>(*this), [this]() {
-    if (id()) {
-      env().Handle( {.id = id(), .type = Event::kUpdate});
-    }
+  env().ExecSub(
+      std::make_shared<nf7::GenericContext>(*this),
+      [this, &env = env(), fid = id()]() {
+        if (env.Handle({ .id = fid, .type = nf7::File::Event::kUpdate })) {
           touch_ = false;
+        }
       });
 }
 File& File::FindOrThrow(std::string_view name) const {

nf7.hh

@@ -288,7 +288,8 @@ class Env {
   virtual void Save() noexcept = 0;
   virtual void Throw(std::exception_ptr&&) noexcept = 0;
 
-  virtual void Handle(const File::Event&) noexcept = 0;
+  // returns the target file if alive
+  virtual nf7::File* Handle(const File::Event&) noexcept = 0;
 
   virtual File* GetFile(File::Id) const noexcept = 0;
   File& GetFileOrThrow(File::Id) const;