Service - GATT client

Github Repo	C Header	C source	JS source
mongoose-os-libs/rpc-service-gattc

Provides RPC service for GATT client.

Methods

• GATTC.Scan - performs BLE scan of the area. Results are returned as an array of objects containing address, name (if present) and RSSI.

$ mos call GATTC.Scan
{
  "results": [
    {
      "addr": "eb:12:dd:51:19:3d",
      "rssi": -48
    },
    {
      "addr": "24:0a:c4:00:31:be",
      "name": "esp32_0031BC",
      "rssi": -36
    }
  ]
}

• GATTC.Open - open connection to a device. Device can be specified by either addr or name. Optional mtu parameter specifies link MTU to be used, the default is 23 bytes (as per standard). Returned value is conn_id which is the connection identifier to be used for later operations.

$ mos call GATTC.Open '{"addr": "eb:12:dd:51:19:3d"}'
{
  "conn_id": 0
}
$ mos call GATTC.Open '{"name": "esp32_0031BC", "mtu": 200}'
{
  "conn_id": 1
}

• GATTS.ListServices - list services provided by device. For each discovered service, its UUID, instance number and primary flag are returned.

$ mos call GATTC.ListServices '{"conn_id": 1}'
{
  "results": [
    {
      "uuid": "1801",
      "instance": 0,
      "primary": true
    },
    {
      "uuid": "1800",
      "instance": 0,
      "primary": true
    },
    {
      "uuid": "5f6d4f53-5f43-4647-5f53-56435f49445f",
      "instance": 0,
      "primary": true
    },
    {
      "uuid": "5f6d4f53-5f52-5043-5f53-56435f49445f",
      "instance": 0,
      "primary": true
    }
  ]
}

In this example, we see two standard services - Generic Access (1800) and Generic Attribute, followed by custom mOS configuration and RPC over GATT services.

• GATTS.ListCharacteristics - list characteristics of a service. For each charateristic, its UUID and properties are returned. Properties are returned a string of up to 8 characters:
  • R - read
  • W - write
  • w - write with no response required
  • N - notify
  • I - indicate
  • B - broadcast
  • E - extended
  • A - auth

$ mos call GATTC.ListCharacteristics '{"conn_id": 1, "svc_uuid": "5f6d4f53-5f43-4647-5f53-56435f49445f"}'
{
  "svc_uuid": "5f6d4f53-5f43-4647-5f53-56435f49445f",
  "results": [
    {
      "uuid": "306d4f53-5f43-4647-5f6b-65795f5f5f30",
      "props": "W"
    },
    {
      "uuid": "316d4f53-5f43-4647-5f76-616c75655f31",
      "props": "WR"
    },
    {
      "uuid": "326d4f53-5f43-4647-5f73-6176655f5f32",
      "props": "W"
    }
  ]
}

• GATTC.Write - write a value to the specified characteristic. conn_id, svc_uuid and char_uuid specify the characteristic, value can be provided either as plain text value or hex-encoded value_hex keys. The following two calls are equivalent

$ mos call GATTC.Write '{"conn_id": 1, "svc_uuid": "5f6d4f53-5f43-4647-5f53-56435f49445f", "char_uuid": "306d4f53-5f43-4647-5f6b-65795f5f5f30", "value": "wifi.ap.enable"}'
null
$ mos call GATTC.Write '{"conn_id": 1, "svc_uuid": "5f6d4f53-5f43-4647-5f53-56435f49445f", "char_uuid": "306d4f53-5f43-4647-5f6b-65795f5f5f30", "value_hex": "776966692e61702e656e61626c65"}'
null

• GATTC.Read - read avlue of a characteristic conn_id, svc_uuid and char_uuid specify the characteristic, value will be returned as either value or value_hex: if value is a string consisting of printable charaters that can be represented as a valid JSON string, result will be in the value key. Otherwise it will be hexified and sent in value_hex.

$ mos call GATTC.Read '{"conn_id": 1, "svc_uuid": "5f6d4f53-5f43-4647-5f53-56435f49445f", "char_uuid": "316d4f53-5f43-4647-5f76-616c75655f31"}'
{
  "value": "true"
}

• GATTC.Close - close the specified connection.

$ mos call GATTC.Close '{"conn_id": 1}'
null

Provisioning one device using another

As a complete example, here is full Bluetooth provisioning process described in this blog post:

$ mos call GATTC.Open '{"name": "esp32_0031BC", "mtu": 200}'
{
  "conn_id": 0
}
$ mos call GATTC.Write '{"conn_id": 0, "svc_uuid": "5f6d4f53-5f43-4647-5f53-56435f49445f", "char_uuid": "306d4f53-5f43-4647-5f6b-65795f5f5f30", "value": "wifi.sta.ssid"}'
null
$ mos call GATTC.Write '{"conn_id": 0, "svc_uuid": "5f6d4f53-5f43-4647-5f53-56435f49445f", "char_uuid": "316d4f53-5f43-4647-5f76-616c75655f31", "value": "Cesanta"}'
null
$ mos call GATTC.Write '{"conn_id": 0, "svc_uuid": "5f6d4f53-5f43-4647-5f53-56435f49445f", "char_uuid": "326d4f53-5f43-4647-5f73-6176655f5f32", "value": "0"}'
null
$ mos call GATTC.Write '{"conn_id": 0, "svc_uuid": "5f6d4f53-5f43-4647-5f53-56435f49445f", "char_uuid": "306d4f53-5f43-4647-5f6b-65795f5f5f30", "value": "wifi.sta.pass"}'
null
$ mos call GATTC.Write '{"conn_id": 0, "svc_uuid": "5f6d4f53-5f43-4647-5f53-56435f49445f", "char_uuid": "316d4f53-5f43-4647-5f76-616c75655f31", "value": "SECRET"}'
null
$ mos call GATTC.Write '{"conn_id": 0, "svc_uuid": "5f6d4f53-5f43-4647-5f53-56435f49445f", "char_uuid": "326d4f53-5f43-4647-5f73-6176655f5f32", "value": "0"}'
null
$ mos call GATTC.Write '{"conn_id": 0, "svc_uuid": "5f6d4f53-5f43-4647-5f53-56435f49445f", "char_uuid": "306d4f53-5f43-4647-5f6b-65795f5f5f30", "value": "wifi.sta.enable"}'
null
$ mos call GATTC.Write '{"conn_id": 0, "svc_uuid": "5f6d4f53-5f43-4647-5f53-56435f49445f", "char_uuid": "316d4f53-5f43-4647-5f76-616c75655f31", "value": "true"}'
null
$ mos call GATTC.Write '{"conn_id": 0, "svc_uuid": "5f6d4f53-5f43-4647-5f53-56435f49445f", "char_uuid": "326d4f53-5f43-4647-5f73-6176655f5f32", "value": "2"}'
null

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