Package gatt provides a Bluetooth Low Energy GATT implementation.
Gatt (Generic Attribute Profile) is the protocol used to write BLE peripherals (servers) and centrals (clients).
As a peripheral, you can create services, characteristics, and descriptors, advertise, accept connections, and handle requests.
As a central, you can scan, connect, discover services, and make requests.
SETUP
gatt supports both Linux and OS X.
On Linux:
To gain complete and exclusive control of the HCI device, gatt uses HCI_CHANNEL_USER (introduced in Linux v3.14) instead of HCI_CHANNEL_RAW. Those who must use an older kernel may patch in these relevant commits from Marcel Holtmann:
Bluetooth: Introduce new HCI socket channel for user operation
Bluetooth: Introduce user channel flag for HCI devices
Bluetooth: Refactor raw socket filter into more readable code
Note that because gatt uses HCI_CHANNEL_USER, once gatt has opened the device no other program may access it.
Before starting a gatt program, make sure that your BLE device is down:
sudo hciconfig
sudo hciconfig hci0 down # or whatever hci device you want to use
If you have BlueZ 5.14+ (or aren't sure), stop the built-in bluetooth server, which interferes with gatt, e.g.:
sudo service bluetooth stop
Because gatt programs administer network devices, they must either be run as root, or be granted appropriate capabilities:
sudo <executable>
# OR
sudo setcap 'cap_net_raw,cap_net_admin=eip' <executable>
<executable>
Usage
Please see godoc.org for documentation.
Examples
Build and run the examples on a native environment (Linux or OS X)
Go is a compiled language, which means to run the examples you need to build them first.
# Build the sample server.
go build examples/server.go
# Start the sample server.
sudo ./server
Alternatively, you can use "go run" to build and run the examples in a single step:
# Build and run the sample server.
sudo go run examples/server.go
Discoverer and explorer demonstrates central (client) functions:
# Discover surrounding peripherals.
sudo go run examples/discoverer.go
# Connect to and explorer a peripheral device.
sudo go run examples/explorer.go <peripheral ID>
Cross-compile and deploy to a target device
# Build and run the server example on a ARMv5 target device.
GOARCH=arm GOARM=5 GOOS=linux go build examples/server.go
cp server <target device>
# Start the server on the target device
sudo ./server
See the server.go, discoverer.go, and explorer.go in the examples/ directory for writing server or client programs that run on Linux and OS X.
Users, especially on Linux platforms, seeking finer-grained control over the devices can see the examples/server_lnx.go for the usage of Option, which are platform specific.
See the rest of the docs for other options and finer-grained control.
Note
Note that some BLE central devices, particularly iOS, may aggressively cache results from previous connections. If you change your services or characteristics, you may need to reboot the other device to pick up the changes. This is a common source of confusion and apparent bugs. For an OS X central, see http://stackoverflow.com/questions/20553957.
Known Issues
Currently OS X vesion does not support subscribing to indications. Please check #32 for the status of this issue.
REFERENCES
gatt started life as a port of bleno, to which it is indebted: https://github.com/sandeepmistry/bleno. If you are having problems with gatt, particularly around installation, issues filed with bleno might also be helpful references.
To try out your GATT server, it is useful to experiment with a generic BLE client. LightBlue is a good choice. It is available free for both iOS and OS X.
gatt is similar to bleno and noble, which offer BLE GATT implementations for node.js.
Gatt is released under a BSD-style license.
