ESPHome configuration for CurrentCost Envi XML parsing and reporting. Uses the RapidXML Header-only library to parse the XML. Works on an ESP32, ESP8266 seems insufficient for the task.

currentcost.h

#include <string>
#include "esphome.h"
#include "rapidxml/rapidxml.hpp"

static const char *TAG = "currentcost";

class CurrentCostSensor : public Component, public UARTDevice {
 public:
  Sensor *ch1 = new Sensor();
  Sensor *ch2 = new Sensor();
  Sensor *ch3 = new Sensor();

  CurrentCostSensor(UARTComponent *parent) : UARTDevice(parent) {}

  void setup() override {
    // nothing to do here
  }

  int readline(int readch, char *buffer, int len)
  {
    static int pos = 0;
    int rpos;

    if (readch > 0) {
      switch (readch) {
        case '\r': // Return on CR
        case '\n': // Return on LF
          rpos = pos;
          pos = 0;  // Reset position index ready for next time
          return rpos;
        default:
          if (pos < len-1) {
            buffer[pos++] = readch;
            buffer[pos] = 0;
          }
      }
    }
    // No end of line has been found, so return -pos to show how far we have got.
    return -pos;
  }

  boolean expect_node(rapidxml::xml_node<> *node, std::string name) {
    if (node && node->name() != name) {
      ESP_LOGD(TAG, "Unexpected node: '%s', expected '%s'", node->name(), name.c_str());
      return false;
    }
    return true;
  }

  void loop() override {
    const int max_line_length = 1024;
    static char buffer[max_line_length];
    while (available()) {
      int got = readline(read(), buffer, max_line_length);
      if (got > 0) {
        ESP_LOGD(TAG, "Read: '%s'", buffer);
        try {
          rapidxml::xml_document<> *xml_doc = new rapidxml::xml_document<>();
          xml_doc->parse<0> (buffer);
          rapidxml::xml_node<> *node, *watts;

          node = xml_doc->first_node();
          if (!expect_node(node, "msg")) return;

          node = node->first_node();
          if (!expect_node(node, "src")) return;

          node = node->next_sibling();
          if (!expect_node(node, "dsb")) return;

          node = node->next_sibling();
          if (!expect_node(node, "time")) return;

          node = node->next_sibling();
          if (!expect_node(node, "tmpr")) return;

          node = node->next_sibling();
          if (!expect_node(node, "sensor")) return;

          node = node->next_sibling();
          if (!expect_node(node, "id")) return;

          node = node->next_sibling();
          if (!expect_node(node, "type")) return;

          node = node->next_sibling();
          if (!expect_node(node, "ch1")) return;
          watts = node->first_node();
          if (!expect_node(watts, "watts")) return;
          ch1->publish_state(atof(watts->value()));

          node = node->next_sibling();
          if (!expect_node(node, "ch2")) return;
          watts = node->first_node();
          if (!expect_node(watts, "watts")) return;
          ch2->publish_state(atof(watts->value()));

          node = node->next_sibling();
          if (!expect_node(node, "ch3")) return;
          watts = node->first_node();
          if (!expect_node(watts, "watts")) return;
          ch3->publish_state(atof(watts->value()));

        } catch (rapidxml::parse_error& e) {
            ESP_LOGD(TAG, "Parse error: %s", e.what());
        } catch (std::exception& e) {
            ESP_LOGD(TAG, "Caught exception: %s", e.what());
        }
      }
    }
  }
};

currentcost.yaml

esphome:
  name: currentcost
  platform: esp32
  board: esp32dev
  platformio_options:
    upload_speed: 460800
    build_flags: -DRAPIDXML_STATIC_POOL_SIZE=1024 -DRAPIDXML_DYNAMIC_POOL_SIZE=1024
    build_unflags: -fno-exceptions
  includes:
     - rapidxml
     - currentcost.h

wifi:
  ssid: !secret wifi_ssid
  password: !secret wifi_password

# Enable logging
logger:

# Enable Home Assistant API
api:

ota:

time:
  - platform: homeassistant
    id: homeassistant_time

text_sensor:
  - platform: version
    name: $name ESPHome Version
  - platform: wifi_info
    ip_address:
      name: $name IP
    ssid:
      name: $name SSID
    bssid:
      name: $name BSSID

switch:
  - platform: restart
    name: $name Restart

binary_sensor:
  - platform: status
    name: $name Status

sensor:
  - platform: uptime
    name: $name uptime

  - platform: wifi_signal
    name: $name WiFi Signal
    update_interval: 60s

  - platform: custom
    lambda: |-
      auto currentcost = new CurrentCostSensor(id(uart_bus));
      App.register_component(currentcost);
      return {currentcost->ch1, currentcost->ch2, currentcost->ch3};
    sensors:
      - id: "ch1"
        name: "currentcost_ch1"
        unit_of_measurement: W
        accuracy_decimals: 0
      - id: "ch2"
        name: "currentcost_ch2"
        unit_of_measurement: W
        accuracy_decimals: 0
      - id: "ch3"
        name: "currentcost_ch3"
        unit_of_measurement: W
        accuracy_decimals: 0

uart:
  id: uart_bus
  rx_pin: GPIO3
  baud_rate: 57600
  rx_buffer_size: 1024