feat: capture peak memory usage at the of request and expose it to via context and caddy replacer vars

This captures peak memory usage similar to FPM and Apache2 SAPIs.
To propagate this back to Go we store it in FrankenPHP context first, before retrieving it in embedder / runtime (e.g. Caddy) from context.

Using in Caddy:
```
  log_append memory_usage {http.frankenphp.memory_usage}
  log_append script {http.frankenphp.script}
```

Author: ikrestov

caddy/module.go

@@ -235,7 +235,17 @@ func (f *FrankenPHPModule) ServeHTTP(w http.ResponseWriter, r *http.Request, _ c
 
 	// TODO: set caddyhttp.ServerHeader when https://github.com/caddyserver/caddy/pull/7338 will be released
 	w.Header()["Server"] = serverHeader
-	if err = frankenphp.ServeHTTP(w, fr); err != nil && !errors.As(err, &frankenphp.ErrRejected{}) {
+	err = frankenphp.ServeHTTP(w, fr)
+
+	// Retrieve and add stats to the Caddy Replacer
+	stats, ok := frankenphp.StatusFromContext(fr.Context())
+	if ok {
+		repl.Set("http.frankenphp.memory_usage", stats.MemoryUsage)
+		repl.Set("http.frankenphp.script", stats.Script)
+		repl.Set("http.frankenphp.script_filename", stats.ScriptFilename)
+	}
+
+	if err != nil && !errors.As(err, &frankenphp.ErrRejected{}) {
 		return caddyhttp.Error(http.StatusInternalServerError, err)
 	}
 

context.go

@@ -38,6 +38,14 @@ type frankenPHPContext struct {
 
 	done      chan any
 	startedAt time.Time
+
+	memoryUsage uint64
+}
+
+type Stats struct {
+	MemoryUsage    uint64
+	Script         string
+	ScriptFilename string
 }
 
 type contextHolder struct {

frankenphp.c

@@ -609,6 +609,8 @@ static zend_module_entry frankenphp_module = {
     STANDARD_MODULE_PROPERTIES};
 
 static void frankenphp_request_shutdown() {
+  go_frankenphp_set_memory_peak_usage(thread_index, zend_memory_peak_usage(1));
+
   frankenphp_free_request_context();
   php_request_shutdown((void *)0);
 }

frankenphp.go

@@ -382,6 +382,19 @@ func Shutdown() {
 	resetGlobals()
 }
 
+// Stats returns FrankenPHP-specific execution stats from the given context.
+func StatusFromContext(ctx context.Context) (Stats, bool) {
+	fc, ok := fromContext(ctx)
+	if !ok {
+		return Stats{}, false
+	}
+	return Stats{
+		MemoryUsage:    fc.memoryUsage,
+		Script:         fc.scriptName,
+		ScriptFilename: fc.scriptFilename,
+	}, true
+}
+
 // ServeHTTP executes a PHP script according to the given context.
 func ServeHTTP(responseWriter http.ResponseWriter, request *http.Request) error {
 	h := responseWriter.Header()

phpthread.go

@@ -173,6 +173,13 @@ func go_frankenphp_after_script_execution(threadIndex C.uintptr_t, exitStatus C.
 	thread.Unpin()
 }
 
+//export go_frankenphp_set_memory_peak_usage
+func go_frankenphp_set_memory_peak_usage(threadIndex C.uintptr_t, memoryPeakUsage C.uint64_t) {
+	thread := phpThreads[threadIndex]
+	fc := thread.frankenPHPContext()
+	fc.memoryUsage = uint64(memoryPeakUsage)
+}
+
 //export go_frankenphp_on_thread_shutdown
 func go_frankenphp_on_thread_shutdown(threadIndex C.uintptr_t) {
 	thread := phpThreads[threadIndex]