From bf51c38975a6bae45ab3d6cb0588f48834d3ddc0 Mon Sep 17 00:00:00 2001
From: Ben Meadors <benmmeadors@gmail.com>
Date: Fri, 5 Sep 2025 07:18:03 -0500
Subject: [PATCH] Don't add heap allocations while debugging the heap

---
 src/Power.cpp | 35 ++++++++++++++++++++++++-----------
 1 file changed, 24 insertions(+), 11 deletions(-)

diff --git a/src/Power.cpp b/src/Power.cpp
index a123fe984..06c6a9089 100644
--- a/src/Power.cpp
+++ b/src/Power.cpp
@@ -833,16 +833,25 @@ void Power::readPowerStatus()
     newStatus.notifyObservers(&powerStatus2);
 #ifdef DEBUG_HEAP
     if (lastheap != memGet.getFreeHeap()) {
-        std::string threadlist = "Threads running:";
+        // Use stack-allocated buffer to avoid heap allocations in monitoring code
+        char threadlist[256] = "Threads running:";
+        int threadlistLen = strlen(threadlist);
         int running = 0;
         for (int i = 0; i < MAX_THREADS; i++) {
             auto thread = concurrency::mainController.get(i);
             if ((thread != nullptr) && (thread->enabled)) {
-                threadlist += vformat(" %s", thread->ThreadName.c_str());
+                // Use snprintf to safely append to stack buffer without heap allocation
+                int remaining = sizeof(threadlist) - threadlistLen - 1;
+                if (remaining > 0) {
+                    int written = snprintf(threadlist + threadlistLen, remaining, " %s", thread->ThreadName.c_str());
+                    if (written > 0 && written < remaining) {
+                        threadlistLen += written;
+                    }
+                }
                 running++;
             }
         }
-        LOG_DEBUG(threadlist.c_str());
+        LOG_DEBUG(threadlist);
         LOG_DEBUG("Heap status: %d/%d bytes free (%d), running %d/%d threads", memGet.getFreeHeap(), memGet.getHeapSize(),
                   memGet.getFreeHeap() - lastheap, running, concurrency::mainController.size(false));
         lastheap = memGet.getFreeHeap();
@@ -856,15 +865,19 @@ void Power::readPowerStatus()
         sprintf(mac, "!%02x%02x%02x%02x", dmac[2], dmac[3], dmac[4], dmac[5]);
 
         auto newHeap = memGet.getFreeHeap();
-        std::string heapTopic =
-            (*moduleConfig.mqtt.root ? moduleConfig.mqtt.root : "msh") + std::string("/2/heap/") + std::string(mac);
-        std::string heapString = std::to_string(newHeap);
-        mqtt->pubSub.publish(heapTopic.c_str(), heapString.c_str(), false);
+        // Use stack-allocated buffers to avoid heap allocations in monitoring code
+        char heapTopic[128];
+        snprintf(heapTopic, sizeof(heapTopic), "%s/2/heap/%s", (*moduleConfig.mqtt.root ? moduleConfig.mqtt.root : "msh"), mac);
+        char heapString[16];
+        snprintf(heapString, sizeof(heapString), "%u", newHeap);
+        mqtt->pubSub.publish(heapTopic, heapString, false);
+
         auto wifiRSSI = WiFi.RSSI();
-        std::string wifiTopic =
-            (*moduleConfig.mqtt.root ? moduleConfig.mqtt.root : "msh") + std::string("/2/wifi/") + std::string(mac);
-        std::string wifiString = std::to_string(wifiRSSI);
-        mqtt->pubSub.publish(wifiTopic.c_str(), wifiString.c_str(), false);
+        char wifiTopic[128];
+        snprintf(wifiTopic, sizeof(wifiTopic), "%s/2/wifi/%s", (*moduleConfig.mqtt.root ? moduleConfig.mqtt.root : "msh"), mac);
+        char wifiString[16];
+        snprintf(wifiString, sizeof(wifiString), "%d", wifiRSSI);
+        mqtt->pubSub.publish(wifiTopic, wifiString, false);
     }
 #endif