Added explicit settings to control segmented write length and delay

README.md

@@ -183,6 +183,14 @@ void setOptions(int keepAlive, bool cleanSession, int timeout);
 - The `cleanSession` option controls the session retention on the broker side (default: true).
 - The `timeout` option controls the default timeout for all commands in milliseconds (default: 1000).
 
+```c++
+void setNetworkSegmentedWrite(size_t segmentLength, uint32_t writeDelayMs);
+```
+
+- The `segmentLength` option controls maximum segment write length for each successive segmented write into network buffer (default: 65535).
+- The `writeDelayMs` option controls delay in ms between each successive segmented write into network buffer (default: 0).
+- This function controls the flow of data into the network buffer, helping to prevent buffer overflows and network congestion, particularly when handling large payloads.
+
 Set a custom clock source "custom millis" callback to enable deep sleep applications:
 
 ```c++

src/MQTTClient.cpp

@@ -91,7 +91,29 @@ inline lwmqtt_err_t lwmqtt_arduino_network_write(void *ref, uint8_t *buffer, siz
   auto n = (lwmqtt_arduino_network_t *)ref;
 
   // write bytes
-  *sent = n->client->write(buffer, len);
+  size_t partial_written = 0;
+  size_t written = 0;
+
+  while (true) {
+    if (len - written > n->segmentLength) {
+      partial_written = n->client->write(buffer + written, n->segmentLength);
+      written += partial_written;
+    }
+    else {
+      partial_written = n->client->write(buffer + written, len - written);
+      written += partial_written;
+      break;
+    }
+
+    delay(n->writeDelayMs);
+
+    if (partial_written <= 0) {
+      return LWMQTT_NETWORK_FAILED_WRITE;
+    }
+  }
+
+  *sent = written;
+
   if (*sent <= 0) {
     return LWMQTT_NETWORK_FAILED_WRITE;
   }
@@ -195,6 +217,9 @@ void MQTTClient::begin(Client &_client) {
 
   // set callback
   lwmqtt_set_callback(&this->client, (void *)&this->callback, MQTTClientHandler);
+
+  this->network.segmentLength = this->_segmentLength;
+  this->network.writeDelayMs = this->_writeDelayMs;
 }
 
 void MQTTClient::onMessage(MQTTClientCallbackSimple cb) {
@@ -314,6 +339,14 @@ void MQTTClient::setCleanSession(bool _cleanSession) { this->cleanSession = _cle
 
 void MQTTClient::setTimeout(int _timeout) { this->timeout = _timeout; }
 
+void MQTTClient::setNetworkSegmentedWrite(size_t segmentLength, uint32_t writeDelayMs) {
+  this->_segmentLength = segmentLength;
+  this->_writeDelayMs = writeDelayMs;
+
+  this->network.segmentLength = this->_segmentLength;
+  this->network.writeDelayMs = this->_writeDelayMs;
+}
+
 void MQTTClient::dropOverflow(bool enabled) {
   // configure drop overflow
   lwmqtt_drop_overflow(&this->client, enabled, &this->_droppedMessages);

src/MQTTClient.h

@@ -41,6 +41,8 @@ typedef struct {
 
 typedef struct {
   Client *client;
+  size_t segmentLength;
+  uint32_t writeDelayMs;
 } lwmqtt_arduino_network_t;
 
 class MQTTClient;
@@ -93,6 +95,9 @@ class MQTTClient {
   lwmqtt_err_t _lastError = (lwmqtt_err_t)0;
   uint32_t _droppedMessages = 0;
 
+  size_t _segmentLength = 65535;
+  uint32_t _writeDelayMs = 0;
+
  public:
   void *ref = nullptr;
 
@@ -141,6 +146,8 @@ class MQTTClient {
     this->setTimeout(_timeout);
   }
 
+  void setNetworkSegmentedWrite(size_t segmentLength, uint32_t writeDelayMs);
+
   void dropOverflow(bool enabled);
   uint32_t droppedMessages() { return this->_droppedMessages; }