fix: remove constructor.Reset() from S7Client/S7Server destructors

[JordiB-Inserma]

Summary

S7Client and S7Server destructors were calling constructor.Reset() on a static Nan::Persistent<FunctionTemplate>, which destroys the V8 constructor template shared across all instances. This causes segfaults on Linux when applications create and destroy S7Client instances repeatedly (e.g. SCADA/HMI reconnection loops like FUXA).

Root cause

constructor is a static class member initialized once during module load (Init). It stores the FunctionTemplate that V8 uses to create new instances. Both ~S7Client() and ~S7Server() were calling constructor.Reset(), which releases the persistent handle to the static FunctionTemplate.

Since this is a static resource shared across ALL instances:

1. new snap7.S7Client() — works, FunctionTemplate alive
2. Instance destroyed (GC/reference lost) → constructor.Reset() destroys the static template
3. Next new snap7.S7Client() → V8's internal constructor resolution fails → SEGFAULT

The crash is non-deterministic and depends on V8 GC timing. On Linux, the GC is more aggressive, making this crash frequent in production SCADA systems.

Fix

Remove constructor.Reset() from both ~S7Client() (node_snap7_client.cpp:722) and ~S7Server() (node_snap7_server.cpp:682). The static FunctionTemplate should live for the lifetime of the module, not per-instance.

Changes

File	Change
src/node_snap7_client.cpp	Removed constructor.Reset() from ~S7Client()
src/node_snap7_server.cpp	Removed constructor.Reset() from ~S7Server()

Stack trace before fix (Linux)

Thread 1 "FUXA" received signal SIGSEGV, Segmentation fault.
#0  v8::internal::ApiNatives::InstantiateFunction(...)
#1  v8::FunctionTemplate::GetFunction(v8::Local<v8::Context>)
#2  node_snap7::S7Client::New(Nan::FunctionCallbackInfo<v8::Value> const&)

Related

• Upstream pthread fix: davenardella/snap7#29 — prerequisite for full Linux stability (fixes undefined behavior when joining detached threads)
• Upstream issues: davenardella/snap7#19, #23
• Environment: Linux, Node.js 18+, node-snap7 1.0.9, FUXA SCADA v1.3.3