[e131] Remove unnecessary heap allocation from packet receive loop

The received data was already in stack buffer buf[1460], but was being
copied into a std::vector just to satisfy the packet_() signature.
E1.31 runs at up to 44 Hz per universe, so this caused ~44 alloc/free
cycles per second per universe.

Change packet_() to accept const uint8_t* + size_t and pass the stack
buffer directly. This is an internal method so there is no API breakage.

esphome/components/e131/e131.cpp

@@ -55,7 +55,6 @@ void E131Component::setup() {
 }
 
 void E131Component::loop() {
-  std::vector<uint8_t> payload;
   E131Packet packet;
   int universe = 0;
   uint8_t buf[1460];
@@ -64,11 +63,9 @@ void E131Component::loop() {
   if (len == -1) {
     return;
   }
-  payload.resize(len);
-  memmove(&payload[0], buf, len);
 
-  if (!this->packet_(payload, universe, packet)) {
-    ESP_LOGV(TAG, "Invalid packet received of size %zu.", payload.size());
+  if (!this->packet_(buf, (size_t) len, universe, packet)) {
+    ESP_LOGV(TAG, "Invalid packet received of size %zd.", len);
     return;
   }
 

esphome/components/e131/e131.h

@@ -38,7 +38,7 @@ class E131Component : public esphome::Component {
   void set_method(E131ListenMethod listen_method) { this->listen_method_ = listen_method; }
 
  protected:
-  bool packet_(const std::vector<uint8_t> &data, int &universe, E131Packet &packet);
+  bool packet_(const uint8_t *data, size_t len, int &universe, E131Packet &packet);
   bool process_(int universe, const E131Packet &packet);
   bool join_igmp_groups_();
   void join_(int universe);

esphome/components/e131/e131_packet.cpp

@@ -116,11 +116,11 @@ void E131Component::leave_(int universe) {
   ESP_LOGD(TAG, "Left %d universe for E1.31.", universe);
 }
 
-bool E131Component::packet_(const std::vector<uint8_t> &data, int &universe, E131Packet &packet) {
-  if (data.size() < E131_MIN_PACKET_SIZE)
+bool E131Component::packet_(const uint8_t *data, size_t len, int &universe, E131Packet &packet) {
+  if (len < E131_MIN_PACKET_SIZE)
     return false;
 
-  auto *sbuff = reinterpret_cast<const E131RawPacket *>(&data[0]);
+  auto *sbuff = reinterpret_cast<const E131RawPacket *>(data);
 
   if (memcmp(sbuff->acn_id, ACN_ID, sizeof(sbuff->acn_id)) != 0)
     return false;

esphome/components/modbus/modbus.cpp

@@ -219,50 +219,39 @@ void Modbus::send(uint8_t address, uint8_t function_code, uint16_t start_address
     return;
   }
 
-  static constexpr size_t ADDR_SIZE = 1;
-  static constexpr size_t FC_SIZE = 1;
-  static constexpr size_t START_ADDR_SIZE = 2;
-  static constexpr size_t NUM_ENTITIES_SIZE = 2;
-  static constexpr size_t BYTE_COUNT_SIZE = 1;
-  static constexpr size_t MAX_PAYLOAD_SIZE = std::numeric_limits<uint8_t>::max();
-  static constexpr size_t CRC_SIZE = 2;
-  static constexpr size_t MAX_FRAME_SIZE =
-      ADDR_SIZE + FC_SIZE + START_ADDR_SIZE + NUM_ENTITIES_SIZE + BYTE_COUNT_SIZE + MAX_PAYLOAD_SIZE + CRC_SIZE;
-  uint8_t data[MAX_FRAME_SIZE];
-  size_t pos = 0;
-
-  data[pos++] = address;
-  data[pos++] = function_code;
+  std::vector<uint8_t> data;
+  data.push_back(address);
+  data.push_back(function_code);
   if (this->role == ModbusRole::CLIENT) {
-    data[pos++] = start_address >> 8;
-    data[pos++] = start_address >> 0;
+    data.push_back(start_address >> 8);
+    data.push_back(start_address >> 0);
     if (function_code != ModbusFunctionCode::WRITE_SINGLE_COIL &&
         function_code != ModbusFunctionCode::WRITE_SINGLE_REGISTER) {
-      data[pos++] = number_of_entities >> 8;
-      data[pos++] = number_of_entities >> 0;
+      data.push_back(number_of_entities >> 8);
+      data.push_back(number_of_entities >> 0);
     }
   }
 
   if (payload != nullptr) {
     if (this->role == ModbusRole::SERVER || function_code == ModbusFunctionCode::WRITE_MULTIPLE_COILS ||
         function_code == ModbusFunctionCode::WRITE_MULTIPLE_REGISTERS) {  // Write multiple
-      data[pos++] = payload_len;                                          // Byte count is required for write
+      data.push_back(payload_len);                                        // Byte count is required for write
     } else {
       payload_len = 2;  // Write single register or coil
     }
     for (int i = 0; i < payload_len; i++) {
-      data[pos++] = payload[i];
+      data.push_back(payload[i]);
     }
   }
 
-  auto crc = crc16(data, pos);
-  data[pos++] = crc >> 0;
-  data[pos++] = crc >> 8;
+  auto crc = crc16(data.data(), data.size());
+  data.push_back(crc >> 0);
+  data.push_back(crc >> 8);
 
   if (this->flow_control_pin_ != nullptr)
     this->flow_control_pin_->digital_write(true);
 
-  this->write_array(data, pos);
+  this->write_array(data);
   this->flush();
 
   if (this->flow_control_pin_ != nullptr)
@@ -272,7 +261,7 @@ void Modbus::send(uint8_t address, uint8_t function_code, uint16_t start_address
 #if ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERBOSE
   char hex_buf[format_hex_pretty_size(MODBUS_MAX_LOG_BYTES)];
 #endif
-  ESP_LOGV(TAG, "Modbus write: %s", format_hex_pretty_to(hex_buf, data, pos));
+  ESP_LOGV(TAG, "Modbus write: %s", format_hex_pretty_to(hex_buf, data.data(), data.size()));
 }
 
 // Helper function for lambdas