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esp_uMQTT_broker

An MQTT Broker/Client with scripting support on the ESP8266

This program enables the ESP8266 to become the central node in a small distributed IoT system. It implements an MQTT Broker and a simple scripted rule engine with event/action statements that links together the MQTT sensors and actors. It can act as STA, as AP, or as both and it can connect to another MQTT broker (i.e. in the cloud). Here it can act as bridge and forward and rewrite topics in both directions. Also it can parse JSON structures, send basic HTTP GET requests and do basic I/O: i.e. read and write to local GPIO pins, react on timers and GPIO interrupts, drive GPIO pins with PWM, and read the ADC.

Find a video that explains the ideas and the architecture of the project at: https://www.youtube.com/watch?v=0K9q4IuB_oA

Usage

In the user directory there is the main program that serves as a stand-alone MQTT broker, client and bridge. The program starts with the following default configuration:

  • ssid: ssid, password: password
  • ap_ssid: MyAP, ap_password: none, ap_on: 1, ap_open: 1
  • network: 192.168.4.0/24

This means it connects to the internet via AP ssid,password and offers an open AP with ap_ssid MyAP. This default can be changed in the file user_config.h. The default can be overwritten and persistenly saved to flash by using a console interface. This console is available either via the serial port at 115200 baud or via tcp port 7777 (e.g. "telnet 192.168.4.1 7777" from a connected STA).

Use the following commands for an initial setup:

  • set ssid your_home_router's_SSID
  • set password your_home_router's_password
  • set ap_ssid ESP's_ssid
  • set ap_password ESP's_password
  • show (to check the parameters)
  • save
  • reset

After reboot it will connect to your home router and itself is ready for stations to connect.

The console understands the following commands:

General commands:

  • help: prints a short help message
  • show [config|stats]: prints the current config or some status information and statistics
  • save: saves the current config parameters to flash
  • lock [password]: saves and locks the current config, changes are not allowed. Password can be left open if already set before
  • unlock password: unlocks the config, requires password from the lock command
  • reset [factory]: resets the esp, 'factory' optionally resets WiFi params to default values (works on a locked device only from serial console)
  • set speed [80|160]: sets the CPU clock frequency (default 80 Mhz)
  • set config_port portno: sets the port number of the console login (default is 7777, 0 disables remote console config)
  • set config_access mode: controls the networks that allow config access (0: no access, 1: only internal, 2: only external, 3: both (default))
  • quit: terminates a remote session

WiFi and network related commands:

  • set [ssid|password] value: changes the settings for the uplink AP (WiFi config of your home-rou- set [ap_ssid|ap_password] value: changes the settings for the soft-AP of the ESP (for your stations)ter)
  • set ap_on [0|1]: selects, whether the soft-AP is disabled (ap_on=0) or enabled (ap_on=1, default)
  • set ap_open [0|1]: selects, whether the soft-AP uses WPA2 security (ap_open=0, automatic, if an ap_password is set) or open (ap_open=1)
  • set auto_connect [0|1]: selects, whether the WiFi client should automatically retry to connect to the uplink AP (default: on=1)
  • set network ip-addr: sets the IP address of the SoftAP's network, network is always /24, esp_uMQTT_broker is always x.x.x.1
  • set dns dns-addr: sets a static DNS address
  • set dns dhcp: configures use of the dynamic DNS address from DHCP, default
  • set ip ip-addr: sets a static IP address for the ESP in the uplink network
  • set ip dhcp: configures dynamic IP address for the ESP in the uplink network, default
  • set netmask netmask: sets a static netmask for the uplink network
  • set gw gw-addr: sets a static gateway address in the uplink network
  • set mdns_mode [0|1|2]: selects, which interface should be announced via mDNS (0=none (default), 1 = STA, 2 = SoftAP)
  • scan: does a scan for APs

While the user interface looks similar to my esp_wifi_repeater at https://github.com/martin-ger/esp_wifi_repeater this does NO NAT routing. AP and STA network are stricly separated and there is no routing in between. The only possible connection via both networks is the uMQTT broker that listens on both interfaces.

MQTT broker related command:

  • show [mqtt]: prints the current config or status information of the MQTT broker
  • set broker_user unsername: sets the username for authentication of MQTT clients ("none" if no auth, default)
  • set broker_password password: sets the password for authentication of MQTT clients ("none" if empty, default)
  • set broker_access mode: controls the networks that allow MQTT broker access (0: no access, 1: only internal, 2: only external, 3: both (default))
  • set broker_subscriptions max: sets the max number of subscription the broker can store (default: 30)
  • set broker_retained_messages max: sets the max number of retained messages the broker can store (default: 30)

MQTT client/bridging functionality

The broker comes with a "local" and a "remote" client, which means, the broker itself can publish and subscribe topics. The "local" client is a client to the own broker (without the need of an additional TCP connection).

By default the "remote" MQTT client is disabled. It can be enabled by setting the config parameter "mqtt_host" to a hostname different from "none". To configure the "remote" MQTT client you can set the following parameters:

  • set mqtt_host IP_or_hostname: IP or hostname of the MQTT broker ("none" disables the MQTT client)
  • set mqtt_user username: Username for authentication ("none" if no authentication is required at the broker)
  • set mqtt_user password: Password for authentication
  • set mqtt_id clientId: Id of the client at the broker (default: "ESPRouter_xxxxxx" derived from the MAC address)
  • publish [local|remote] [topic] [data]: this publishes a topic (mainly for testing)

Scripting

The esp_uMQTT_broker comes with a build-in scripting engine. A script enables the ESP not just to act as a passive broker but to react on events (publications and timing events), to send out its own items and handle local I/O. Details on syntax and semantics of the scripting language can be found here: https://github.com/martin-ger/esp_mqtt/blob/master/SCRIPTING.md . Examples of scripts are in the "scripts" directory.

The script specific CLI commands are:

  • script [portno|delete]: opens port for upload of scripts or deletes the current script
  • show script [line_no]: dumps the currently active script starting with the given line (dumpy only about 1 KB, repeat command for more lines)
  • set @[num] value: sets the flash variable "num" (for use in scripts) to the given inital value (must be shorter than 63 chars)
  • set pwm_period period: sets the PWM period in terms of 200ns slots (default: 5000, = 0.1ms ^= 1KHz)
  • show vars: dumps all variables of the current program incl. the persistent flash variables
  • set script_logging [0|1]: switches logging of script execution on or off (not permanently stored in the configuration)

Scripts with size up to 4KB are uploaded to the esp_uMQTT_broker using a network interface. Start the upload with "script " on the concole of the ESP, e.g.:

CMD>script 2000
Waiting for script upload on port 2000
CMD>

Now the ESP listens on the given port for an incoming connection and stores anything it receives as new script. Upload a file using netcat, e.g.:

$ netcat 192.168.178.29 2000 < user/demo_script2

The ESP will store the file and immediatly checks the syntax of the script:

CMD>script 2000
Waiting for script upload on port 2000
Script upload completed (451 Bytes)
Syntax okay
CMD>

You can examine the currently loaded script using the "show script" command. It only displays about 1KB of a script. If you need to see more, use "show script <line_no>" with a higher starting line. Newly loaded scripts are stored persistently in flash and will be executed after next reset if they contain no syntax errors. "script delete" stops script execution and deleted a script from flash.

NTP Support

NTP time is supported and timestamps are only available if the sync with an NTP server is done. By default the NTP client is enabled and set to "1.pool.ntp.org". It can be changed by setting the config parameter "ntp_server" to a hostname or an IP address. An ntp_server of "none" will disable the NTP client. Also you can set the "ntp_timezone" to an offset from GMT in hours. The system time will be synced with the NTP server every "ntp_interval" seconds. Here it uses NOT the full NTP calculation and clock drift compensation. Instead it will just set the local time to the latest received time.

After NTP sync has been completed successfully once, the local time will be published every second under the topic "$SYS/broker/time" in the format "hh:mm:ss". You can also query the NTP time using the "time" command from the commandline.

  • set ntp_server IP_or_hostname: sets the name or IP of an NTP server (default "1.pool.ntp.org", "none" disables NTP)
  • set ntp_interval interval: sets the NTP sync interval in seconds (default 300)
  • set ntp_timezone tz: sets the timezone in hours offset (default 0)
  • time: prints the current time as ddd hh:mm:ss

mDNS

mDNS is supported and depending on "mdns_mode" the broker responds on the name "mqtt.local" with one of its two addresses:

  • set mdns_mode [0|1|2]: selects, which interface address should be announced via mDNS (0=none (default), 1 = STA, 2 = SoftAP)

Building and Flashing

The code can be used in any project that is compiled using the NONOS_SDK or the esp-open-sdk. Also the complete broker in the user directory can be build using the standard SDKs after adapting the variables in the Makefile.

Configure the build options in "user_config.h", then build the esp_uMQTT_broker firmware with "make". "make flash" flashes it onto an esp8266.

If you want to use the precompiled binaries from the firmware directory you can flash them directly on an ESP8266, e.g. with

$ esptool.py --port /dev/ttyUSB0 write_flash -fs 32m 0x00000 firmware/0x00000.bin 0x10000 firmware/0x10000.bin

The MQTT broker library

Thanks to Tuan PM for sharing his MQTT client library https://github.com/tuanpmt/esp_mqtt as a basis with us. The modified code still contains the complete client functionality from the original esp_mqtt lib, but it has been extended by the basic broker service.

The broker does support:

  • MQTT protocoll versions v3.1 and v3.1.1 simultaniously
  • a smaller number of clients (at least 8 have been tested, memory is the issue)
  • retained messages
  • LWT
  • QoS level 0
  • username/password authentication

The broker does not yet support:

  • QoS levels other than 0
  • many TCP(=MQTT) clients
  • non-clear sessions
  • TLS "

Using the esp_uMQTT_broker in an Arduino project

There is a quick-and-dirty hack to add the pure broker functionality (not the CLI and the scripting) to any ESP Arduino project:

  • Go to the install directory of the ESP8266 support package (something like: "[yourArduinoDir]/hardware/esp8266com/esp8266")
  • Look for the file "platform.txt"
  • Search for the line with "compiler.c.elf.libs"
  • Add "-lmqtt" to the libs. Now it should look like:
compiler.c.elf.libs=-lm -lgcc -lhal -lphy -lpp -lnet80211 -lwpa -lcrypto -lmain -lwps -laxtls -lsmartconfig -lmesh -lwpa2 -lmqtt {build.lwip_lib} -lstdc++
  • From this directory go to "cd tools/sdk/lib".
  • Copy "libmqtt.a" from the "firmware" directory of this repository into that location (where the other C-libs of the SDK are).
  • From this directory go to "cd ../include".
  • Copy "mqtt_server.h" from the "Arduino" directory of this repository into that location (where the other include files of the SDK are).
  • Now you can use it in your sketch. Just include
#include "mqtt_server.h"

Now you can use the API as described in the next subsection.

Sample: in the Arduino setup() initialize the WiFi connection (client or SoftAP, whatever you need) and somewhere at the end add these line:

MQTT_server_start(1883, 30, 30);

The MQTT server will now run in the background and you can connect with any MQTT client. Your Arduino project might do other application logic in its loop.

You can find a sample sketch in the "Arduino" directory.

Using the Source Code

The complete broker functionality is included in the mqtt directory and can be integrated into any NONOS SDK (or ESP Arduino) program ("make -f Makefile.orig lib" will build the mqtt code as a C library). You can find a minimal demo in the directory "user_basic". Rename it to "user", adapt "user_config.h", and do the "make" to build a small demo that just starts an MQTT broker without any additional logic.

The broker is started by simply including:

#include "mqtt_server.h"

and then calling

bool MQTT_server_start(uint16_t portno, uint16_t max_subscriptions, uint16_t max_retained_topics);

in the "user_init()" (or Arduino "setup()") function. Now it is ready for MQTT connections on all activated interfaces (STA and/or AP). Please note, that the lib uses two tasks (with prio 1 and 2) for client and broker. Thus, only task with prio 0 is left for a user application.

Your code can locally interact with the broker using these functions:

bool MQTT_local_publish(uint8_t* topic, uint8_t* data, uint16_t data_length, uint8_t qos, uint8_t retain);
bool MQTT_local_subscribe(uint8_t* topic, uint8_t qos);
bool MQTT_local_unsubscribe(uint8_t* topic);

void MQTT_server_onData(MqttDataCallback dataCb);

With these functions you can publish and subscribe topics as a local client like you would with any remote MQTT broker. The provided dataCb is called on each reception of a matching topic, no matter whether it was published from a remote client or the "MQTT_local_publish()" function.

Username/password authentication is provided with the following interface:

typedef bool (*MqttAuthCallback)(const char* username, const char *password, struct espconn *pesp_conn);

void MQTT_server_onAuth(MqttAuthCallback authCb);

typedef bool (*MqttConnectCallback)(struct espconn *pesp_conn);

void MQTT_server_onConnect(MqttConnectCallback connectCb);

If an MqttAuthCallback function is registered with MQTT_server_onAuth(), it is called on each connect request. Based on username, password, and optionally the connection info (e.g. the IP address) the function has to return true for authenticated or false for rejected. If a request provides no username and/or password these parameter strings are empty. If no MqttAuthCallback function is set, each request will be admitted.

The MqttConnectCallback function does a similar check for the connection, but it is called right after the connect request before any internal status is allocated. This is done in order to reject requests from unautorized clients in an early stage.

Limitations on the number of clients

To adjust memory consumption of one MQTT connection and thus the max number of concurrent connections you can redefine MQTT_BUF_SIZE and QUEUE_BUFFER_SIZE in "user_config.h". MQTT_BUF_SIZE is the max. size of pending inbound messages for one connection (and thus also the max. size of a single MQTT message) and QUEUE_BUFFER_SIZE is the max. size of all pending outbound messages for one connection. Currently these parameters are set to 1024 resp. 2048 bytes, resulting in a memory consumption of about 4 KB per connection and a max number of connections of about 8-9 (depending on the memory usage of the rest of the program). When you reduce buffer sizes, e.g. to 512 and 1024 bytes, a single connection requires only about 2.5 KB resulting in up to 13 possible concurrent MQTT connections. In any case you have to increase the number of TCP connections (default 5) first by calling "espconn_tcp_set_max_con(n)" with n, the max. number of concurrent TCP connections, less or equal to 15.

Also there is a hard limitation on the number of STAs connected to the SoftAP, which is 8. I.e. when using the esp_uMQTT_broker only with clients via the SoftAP interface, even with reduced memory consumtion, the limit of different client nodes is still 8, as it is imposed by the binary WiFi driver. Only when used via the STA interface and an external AP you can connect more than 8 MQTT clients.

Thanks