ESP8266MQTTMesh

Self-assembling mesh network built around the MQTT protocol for the ESP8266 with OTA support

Overview

This code provides a library that can build a mesh network between ESP8266 devices that will allow all nodes to communicate with an MQTT broker. At least one node must be able to see a wiFi router, and there must me a host on the WiFi network running the MQTT broker. Nodes cannot (generally) communicate between themselves, but instead forward all messages through the broker. Each node will expose a hidden AP which can be connected to from any other node on the network. Note: hiding the AP does not provide any additional security, but does minimize the clutter of other WiFi clients in the area.

Additionally the library provides an OTA mechanism using the MQTT pathway which can update any/all nodes on the mesh.

This code was developed primarily for the Sonoff line of relays, but should work with any ESP8266 board with sufficient flash memory

Further information about the mesh topology can be found here

Note for version >= 1.0

As of version 1.0 the nodes no longer need to connect to the broker once before use. Nodes can self-identify other nodes automatically and do not store any needed state on the broker. Nodes use the MAC address to identify other nodes, and the ESP8266MQTTMesh code will change the node's MAC address to match the required pattern. The MAC addresses are based on both the node's chipID as well as the mesh password, ensuring that each node will have a unique MAC address as well as that multiple meshes can run in the same area independently.

Also, he ESP8266MQTTMesh code no longer uses the SPIFFS file-system. If you need it, you'll need to initialize it yourself. If the mesh is configured to use SSL between nodes, the SSL certs need to be provided during initalization

OTA

While all nodes must run the same version of the ESP8622MQTTMesh library, each node may run a unique firmware with independent purposes. The main purpose behind this library was to provide a backbone on which several home-automation sensors could be built. As such each node may need different code to achieve its purpose. Because firmwares are large, and memory is limited on the ESP8266 platform, there is only a single memory area to hold the incoming firmware. To ensure that a given firmware is only consumed by the proper nodes, The firmware defines a unique identifier that distinguishes itself from other code. A given firmware is broadcast from the MQTT broker to all nodes, but only nodes with a matching ID will update.

Using the Library

Prerequisites

This library has been converted to use Asynchronous communication for imroved reliability. It requires the following libraries to be installed

• AsyncMqttClient
• ESPAsyncTCP
• Arduino ESP8266 Core version 2.4

PlatformIO is strongly recommended, and installation instructions can be found here).

NOTE: Enabling SSL will add ~70kB to the firmware size, and may make it impossible to use OTA updates depending on firmware and flash size.

If OTA support is desired, the esp8266 module must have at least 1M or Flash (configured as >=784k ROM). The OTA image is stored between the end of the firmware image and the beginning of the filesystem (i.e. not in the filesystem itself) or the end of flash if no filesystem is present. Thus, ithe maximum firmware size is ~ 1/2 the available Flash.

Library initialization

The ESP8266MQTTMesh only requires 2 parameters to initialize, but there are many additional optional parameters:

ESP8266MQTTMesh mesh = ESP8266MQTTMesh::Builder(networks, mqtt_server, mqtt_port).build();

• wifi_conn networks[] Required: A list of SSIDs/BSSIDs/passwords to search for to connect to the wireless network. The list should be terminated with a NULL element.
• const char *mqtt_server Required: Host which runs the MQTT broker
• int mqtt_port Optional: Port which the MQTT broker is running on. Defaults to 1883 if MQTT SSL is not enabled. Defaults to 8883 is MQTT SSL is enabled

Additional Parameters can be enabled via the Builder for example:

ESP8266MQTTMesh mesh = ESP8266MQTTMesh::Builder(networks, mqtt_server, mqtt_port)
                       .setVersion(firmware_ver, firmware_id)
                       .setMeshPassword(password)
                       .build();

These additional parameters are specified before calling build(), and as few or as many can be used as neeeded.

setVersion(firmware_ver, firmware_id)

• const char *firmware_ver: This is a string that idenitfies the firmware. It can be whatever you like. It will be broadcast to the MQTT broker on successful connection
• int firmware_id: This identifies a specific node codebase. Each unique firmware should have its own id, and it should not be changed between revisions of the code

setMqttAuth(username, password)

• const char *username: The username used to login to the MQTT broker
• const char *password: The password used to login to the MQTT broker

setMeshPassword(password)

• const char *password: The password to use when a node connects to another node on the mesh. Default: ESP8266MQTTMesh

setMeshSSID(ssid)

• const char *ssid: The SSID used by mesh nodes. All nodes will use the same SSID, though this isn't noticeable due to nodes using hidden networks. Default: `esp8266_mqtt_mesh

setMeshPort(port)

• int port: Port for mesh nodes to listen on for message parsing. Default: 1884

setTopic(in_topic, out_topic)

• const char *in_topic: MQTT topic prefix for messages sent to the node. Default: esp8266-in/
• const char *out_topic: MQTT topic prefix for messages from the node. Default: esp8266-out/

If SSL support is enabled, the following optional parameters are available:

setMqttSSL(enable, fingerprint)

• bool enable: Enable MQTT SSL support. Default: false
• const uint8_t *fingerprint: Fingerprint to verify MQTT certificate (prevent man-in-the-middle attacks)

setMeshSSL(cert, cert_len, key, key_len, fingerprint)

• const uint8_t *cert: Certificate
• uint32_t cert_len: Certificate length
• const uint8_t *key: Certificate key
• uint32_t key_len: Certificate key length
• uint8_t *fingerprint: Certificate fingerprint (SHA1 of certificate)

Interacting with the mesh

Besides the constructor, the code must call the begin() method during setup, and the loop() method in the main loop

If messages need to be received by the node, execute the callback() function during setup with a function pointer (prototype: void callback(const char *topic, const char *payload))

To send messages to the MQTT broker, use one of the publish methods:

publish(topic, payload, msgCmd)
publish_node(topic, payload, msgCmd)

The publish function sends messages with the out_topic prefix, and will not be relayed to any nodes. The publish_nodes function will send messages with the in_topic prefix and will be relayed back to all nodes

• const char *topic: the message topic (will be appended to the topic-prefix)
• const char *payload: The message to send (must be less than 1152 bytes in length)
• enum MSG_TYPE msgCmd: The MQTT Retail/QoS partameters (optional). Must be one of: MSG_TYPE_NONE, MSG_TYPE_QOS_0, MSG_TYPE_QOS_1, MSG_TYPE_QOS_2, MSG_TYPE_RETAIN_QOS_0, MSG_TYPE_RETAIN_QOS_1, MSG_TYPE_RETAIN_QOS_2. Default: MSG_TYPE_NONE`

SSL support

SSL support is enabled by defining ASYNC_TCP_SSL_ENABLED=1. This must be done globally during build.

Once enabled, SSL can be optionally enabled between the node and the MQTT broker or between mesh nodes (or both).

Using SSL with the MQTT Broker

WARNING: Make sure you do not use SHA512 certificate signatures on your MQTT broker. They are not suppoorted by ESP8266 properly Using an optional fingerprint ensures that the MQTT Broker is the one you expect. Specifying a fingerprint is useful to prevent man-in-the-middle attacks. The fingerprint can be generated by running:

utils/get_mqtt_fingerprint.py --host <MQTT host> --post <MQTT port>

This will also check the signature to make sure it is compatible with ESP8266

Using SSL between mesh nodes

NOTE: Enabling SSL between mesh nodes should not provide additional security, since the mesh connections are already secured via WPA, so enabling this is not recommended

Generate the certificate, key and fingerprint:

utils/gen_server_cert.sh

Add the resulting ssl_cert.h to your project. then add to the Builder setMeshSSL(ssl_cert, ssl_cert_len, ssl_key, ssl_key_len, ssl_fingerprint)