BLE Characteristic Scan

Sometimes you might want to see what services and characeristics a device provides.

You can do this using the NRF Connect app for Android/iOS but sometimes you might want to do it on Espruino too.

Run this code, changing the id at the top to match the device you're interested in (which you can get from NRF.findDevices(print)) and you'll see something like:

Connecting
Connected
Service 0x1800 (hdl=1=>9)
  Characteristic 0x2a00 (hdl=3,desc=2) {broadcast:false,read:true,writeWithoutResponse:false,write:false,notify:false,indicate:false,authenticatedSignedWrites:false}
  Characteristic 0x2a01 (hdl=5,desc=4) {broadcast:false,read:true,writeWithoutResponse:false,write:false,notify:false,indicate:false,authenticatedSignedWrites:false}
  Characteristic 0x2a04 (hdl=7,desc=6) {broadcast:false,read:true,writeWithoutResponse:false,write:false,notify:false,indicate:false,authenticatedSignedWrites:false}
  Characteristic 0x2aa6 (hdl=9,desc=8) {broadcast:false,read:true,writeWithoutResponse:false,write:false,notify:false,indicate:false,authenticatedSignedWrites:false}
Service 0x1801 (hdl=10=>10)
  No Characteristics
Service 6e400001-b5a3-f393-e0a9-e50e24dcca9e (hdl=11=>65535)
  Characteristic 6e400002-b5a3-f393-e0a9-e50e24dcca9e (hdl=13,desc=12) {broadcast:false,read:false,writeWithoutResponse:true,write:true,notify:false,indicate:false,authenticatedSignedWrites:false}
  Characteristic 6e400003-b5a3-f393-e0a9-e50e24dcca9e (hdl=15,desc=14) {broadcast:false,read:false,writeWithoutResponse:false,write:false,notify:true,indicate:false,authenticatedSignedWrites:false}
Disconnected

In this case we're scanning an Espruino device, so we see the 6e400001-b5a3-f393-e0a9-e50e24dcca9e Nordic UART service and RX/TX characteristics in it.

Source Code

NRF.requestDevice({ filters: [{ id: "c9:7b:07:d0:9f:0e random" }] }).then(function(d) {
  device = d;
  console.log("Connecting");
  return device.gatt.connect();
}).then(function(g) {
  gatt = g;
  console.log("Connected");
  return gatt.getPrimaryServices();
}).then(function getServices(services) {
  if (services.length==0) return;
  let service = services.shift();
  print(`Service ${service.uuid} (hdl=${service.start_handle}=>${service.end_handle})`);
  return service.getCharacteristics().then(characteristics => {
    if (characteristics===undefined)
      print("  No Characteristics");
    else characteristics.forEach(char => {
      print(`  Characteristic ${char.uuid} (hdl=${char.handle_value},desc=${char.handle_decl}) ${E.toJS(char.properties)}`);
    });
    return Promise.resolve(services).then(getServices);
  });
}).then(function() {
  gatt.disconnect();
  console.log("Disconnected");
});