Begin crashes with Invalid mbox on esp32 due to MQTT connecting too early

[jbaudoux]

Describe the bug

On ESP32, you cannot open a socket if the network is not established. This means that you cannot start the mqtt connection if the network is not connected. Error message at boot is:
assert failed: tcpip_send_msg_wait_sem IDF/components/lwip/lwip/src/api/tcpip.c:455 (Invalid mbox)

Bug is in MqttClient::begin() that connects without checking network here
https://github.com/sidoh/esp8266_milight_hub/blob/master/lib/MQTT/MqttClient.cpp#L55
That reconnect() line should be removed.

The mqtt connection will be established in the loop when calling MqttClient::handleClient() after checking the network connection here https://github.com/sidoh/esp8266_milight_hub/blob/master/src/main.cpp#L531
i think there is no need to connect in begin.

Steps to reproduce

I guess it depends how fast the network is established.

Expected behavior

Should not crash in begin

Setup information

Firmware version

1.13.1

Output of http://milight-hub.local/about

{"firmware":"milight-hub","version":"1.13.1-beta2","ip_address":"172.19.3.37","reset_reason":"7","variant":"esp32","free_heap":215768,"arduino_version":"v4.4.6-dirty","free_stack":5548,"flash_used":2259,"flash_total":113201,"flash_pct_free":98,"mqtt":{"configured":true,"connected":true,"status":"Connected"},"queue_stats":{"length":0,"dropped_packets":0}}

Output of http://milight-hub.local/settings

{"admin_username":"","admin_password":"","ce_pin":4,"csn_pin":5,"reset_pin":0,"led_pin":-2,"radio_interface_type":"nRF24","packet_repeats":50,"http_repeat_factor":1,"auto_restart_period":0,"mqtt_server":"172.19.3.140","mqtt_username":"","mqtt_password":"","mqtt_topic_pattern":"milight/commands/:device_id/:device_type/:group_id","mqtt_update_topic_pattern":"","mqtt_state_topic_pattern":"milight/state/:device_id/:device_type/:group_id","mqtt_client_status_topic":"milight/client_status","simple_mqtt_client_status":true,"discovery_port":48899,"listen_repeats":3,"state_flush_interval":10000,"mqtt_state_rate_limit":500,"mqtt_debounce_delay":500,"mqtt_retain":true,"packet_repeat_throttle_sensitivity":0,"packet_repeat_throttle_threshold":200,"packet_repeat_minimum":3,"enable_automatic_mode_switching":false,"led_mode_wifi_config":"Fast toggle","led_mode_wifi_failed":"On","led_mode_operating":"Slow blip","led_mode_packet":"Flicker","led_mode_packet_count":3,"hostname":"milight-hub","rf24_power_level":"MAX","rf24_listen_channel":"LOW","wifi_static_ip":"","wifi_static_ip_gateway":"","wifi_static_ip_netmask":"","packet_repeats_per_loop":10,"home_assistant_discovery_prefix":"homeassistant/","wifi_mode":"g","default_transition_period":500,"rf24_channels":["LOW","MID","HIGH"],"device_ids":[],"gateway_configs":[],"group_state_fields":["state","brightness","computed_color","mode","color_temp","color_mode"],"ignored_listen_protocols":[]}

Additional context

Board: esp32dev
Build with pio run --target upload -e esp32

[jbaudoux]

MDNS also fails - reported here #866