KIWI - a bluetooth beacon gateway


KIWI module listens for the BLE beacon advertisements, and forwards them to the specified MQTT server. AWS IoT, Azure, Google IoT Core, IBM Watson, and private MQTT servers are supported. The gateway algorithm is as follows:

  • Connect to the configured MQTT server. Reconnect when a connection is lost
  • Perform a continuous BLE scan, listen for the BLE advertisements
  • When a BLE advertisement is received, report it to the kiwi.pub_topic MQTT topic
  • If the next advertisement is the same as previous, skip reporting
  • Limit the frequency of reports by kiwi.report_interval_ms value
  • When KIWI reconnects to a server, re-report all devices
  • Subscribe to a kiwi.sub_topic. When any message arrives on this topic, re-report all devices
  • This is an example message that gets reported to the MQTT:
  "gw": "esp32-ce12ba",         // Gateway name
  "mac": "7f:d3:87:0b:ac:d5",   // Beacon's MAC address
  "rssi": -16,                  // Signal strength. Can be used for triangulation
  "adv": "02011a14ff4c3e54",    // Beacon advertisement data
  "scan": "04ae45c2"            // Scan response. Only available for active scans

Quick start

  1. Buy an ESP32 device mentioned on the KIWI page
  2. Connect an ESP32 device to your workstation via USB
  3. Follow steps 1,2,3 of mos setup
  4. In the mos UI, run
    mos flash
  5. Follow step 7 of mos setup
  6. Login to the license manager and buy KIWI licenses (one per device)
  7. Execute mos license
  8. Configure MQTT:
    • For generic/private MQTT server, run
      mos config-set mqtt.enable=true mqtt.server=HOST:PORT
    • For AWS, follow AWS guide's "Setup AWS IoT" and "Setup device" chapters
    • For Google, follow GCP guide's "Setup Google IoT Core" and "Setup device" chapters
    • For Azure, follow Azure guide's "Setup Azure IoT Hub" and "Setup device" chapters
    • For Watson, follow Watson guide's "Quick setup" chapter
    • For mDash, follow step 8 of mos setup

When done, you should have your ESP32 device flashed, provisioned to WiFi, connected to the cloud, and reporting devices. Below is an example of M5Stack gateway,

m5stack gateway

reporting data to the

m5stack gateway

Configuring KIWI

KIWI keeps its configuration on a flash filesystem. It could be instected and changed using mos tool. To see an existing configuration, execute mos config-get. Below is the documentation for relevant entries:

"kiwi": {
  "pub_topic": "kiwi",        // Publish topic - devices get reported to it
  "sub_topic": "kiwi_flush",  // Subscribe topic - on message, devices are re-reported
  "qos":  0,                  // Publish QOS
  "report_interval_ms":  0,   // Reporting interval in milliseconds
  "active_scan":  false,      // Do an active or passive BLE scan
  "name_filter":  "",         // Only report devices with this substring in the name
"mqtt": {
  "enable": true,                               // Enable MQTT. Requires a license
  "server": "",    // MQTT server address

In order to change any configuration parameter, execute mos config-set name=value, for example:

mos config-set
mos config-set kiwi.pub_topic=my_cool_topic

Rewriting scan responses

It is possible to define a custom logic to modify received scan results before storing/reporting them. This can be done by uploading an app.js file to the device:

mos put path/to/app.js

Here is how app.js content should look like:


let evo = ffi('void *get_kiwi_ev_descr(void)')();
let mkrsp = ffi('void kiwi_mkrsp(void *, char *, int)');  
let mkadv = ffi('void kiwi_mkadv(void *, char *, int)');

Event.on(Event.baseNumber('KWI'), function(ev, data) {
  let obj = s2o(data, evo);
  print('got kiwi event:', JSON.stringify(obj));

  // Put your response rewrite logic below.
  if (obj.stored_rsp !== '') {
    mkrsp(data, '\x01\x02\x03', 3);   // Rewrite scan resp
    mkadv(data, 'abc321', 6);         // Rewrite adv data
}, null);

print('JS rewrite initialised');

For each scan result, a JavaScript callback function is called. It receives scan data opaque pointer, which could be transformed into the JavaScript object obj with the following fields:

  "addr": "...",          // 6-byte device MAC address
  "adv": "...",           // Adv data
  "stored_adv": "...",    // Stored adv data
  "rsp": "...",           // Scan response
  "stored_rsp": "..."     // Stored scan response

All fields a byte strings. Length could be taken like obj.adv.length. Contents could be examined using at() function, like See for mjs API reference.

For example, to traverse an adv data, do:

    for (let i = 0; i < obj.adv.length; i++) {
       let val =;
       print('Value at index', i, 'is', val);

Functions mkrsp() and mkadv could be used to rewrite response and adv data, respectively. They both take an opaque pointer, and string + length parameter.

If you need to disable rewrite, just remove the app.js:

mos rm app.js

The device needs to be rebooted after app.js change, since app.js is read once at startup.

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