prototooth/gap.go

package bluetooth

import "errors"

var (
	errScanning                  = errors.New("bluetooth: a scan is already in progress")
	errNotScanning               = errors.New("bluetooth: there is no scan in progress")
	errAdvertisementPacketTooBig = errors.New("bluetooth: advertisement packet overflows")
)

// AdvertisementOptions configures an advertisement instance. More options may
// be added over time.
type AdvertisementOptions struct {
	// The (complete) local name that will be advertised. Optional, omitted if
	// this is a zero-length string.
	LocalName string

	// ServiceUUIDs are the services (16-bit or 128-bit) that are broadcast as
	// part of the advertisement packet, in data types such as "complete list of
	// 128-bit UUIDs".
	ServiceUUIDs []UUID

	// Interval in BLE-specific units. Create an interval by using
	// NewAdvertiseInterval.
	Interval AdvertisementInterval
}

// AdvertisementInterval is the advertisement interval in 0.625µs units.
type AdvertisementInterval uint32

// NewAdvertisementInterval returns a new advertisement interval, based on an
// interval in milliseconds.
func NewAdvertisementInterval(intervalMillis uint32) AdvertisementInterval {
	// Convert an interval to units of
	return AdvertisementInterval(intervalMillis * 8 / 5)
}

// Connection is a numeric identifier that indicates a connection handle.
type Connection uint16

// Address contains a Bluetooth address, which is a MAC address plus some extra
// information.
type Address struct {
	// The MAC address of a Bluetooth device.
	MAC

	// Is this address a random address?
	// Bluetooth addresses are roughly split in two kinds: public
	// (IEEE-assigned) addresses and random (not IEEE assigned) addresses.
	// "Random" here doesn't mean it is exactly random but at least it looks
	// random. Sometimes, it contains a hash.
	// For more information:
	// https://www.novelbits.io/bluetooth-address-privacy-ble/
	//
	// This field is unused under Windows and Linux.
	IsRandom bool
}

// ScanResult contains information from when an advertisement packet was
// received. It is passed as a parameter to the callback of the Scan method.
type ScanResult struct {
	// Bluetooth address of the scanned device.
	Address Address

	// RSSI the last time a packet from this device has been received.
	RSSI int16

	// The data obtained from the advertisement data, which may contain many
	// different properties.
	// Warning: this data may only stay valid until the next event arrives. If
	// you need any of the fields to stay alive until after the callback
	// returns, copy them.
	AdvertisementPayload
}

// AdvertisementPayload contains information obtained during a scan (see
// ScanResult). It is provided as an interface as there are two possible
// implementations: an implementation that works with raw data (usually on
// low-level BLE stacks) and an implementation that works with structured data.
type AdvertisementPayload interface {
	// LocalName is the (complete or shortened) local name of the device.
	// Please note that many devices do not broadcast a local name, but may
	// broadcast other data (e.g. manufacturer data or service UUIDs) with which
	// they may be identified.
	LocalName() string

	// Bytes returns the raw advertisement packet, if available. It returns nil
	// if this data is not available.
	Bytes() []byte
}

// AdvertisementFields contains advertisement fields in structured form.
type AdvertisementFields struct {
	// The LocalName part of the advertisement (either the complete local name
	// or the shortened local name).
	LocalName string
}

// advertisementFields wraps AdvertisementFields to implement the
// AdvertisementPayload interface. The methods to implement the interface (such
// as LocalName) cannot be implemented on AdvertisementFields because they would
// conflict with field names.
type advertisementFields struct {
	AdvertisementFields
}

// LocalName returns the underlying LocalName field.
func (p *advertisementFields) LocalName() string {
	return p.AdvertisementFields.LocalName
}

// Bytes returns nil, as structured advertisement data does not have the
// original raw advertisement data available.
func (p *advertisementFields) Bytes() []byte {
	return nil
}

// rawAdvertisementPayload encapsulates a raw advertisement packet. Methods to
// get the data (such as LocalName()) will parse just the needed field. Scanning
// the data should be fast as most advertisement packets only have a very small
// (3 or so) amount of fields.
type rawAdvertisementPayload struct {
	data [31]byte
	len  uint8
}

// Bytes returns the raw advertisement packet as a byte slice.
func (buf *rawAdvertisementPayload) Bytes() []byte {
	return buf.data[:buf.len]
}

// findField returns the data of a specific field in the advertisement packet.
func (buf *rawAdvertisementPayload) findField(fieldType byte) []byte {
	data := buf.Bytes()
	for len(data) >= 2 {
		fieldLength := data[0]
		if int(fieldLength)+1 > len(data) {
			// Invalid field length.
			return nil
		}
		if fieldType == data[1] {
			return data[2 : fieldLength+1]
		}
		data = data[fieldLength+1:]
	}
	return nil
}

// LocalName returns the local name (complete or shortened) in the advertisement
// payload.
func (buf *rawAdvertisementPayload) LocalName() string {
	b := buf.findField(9) // Complete Local Name
	if len(b) != 0 {
		println("complete")
		return string(b)
	}
	b = buf.findField(8) // Shortened Local Name
	if len(b) != 0 {
		println("shortened")
		return string(b)
	}
	return ""
}

// addFromOptions constructs a new advertisement payload (assumed to be empty
// before the call) from the advertisement options. It returns true if it fits,
// false otherwise.
func (buf *rawAdvertisementPayload) addFromOptions(options AdvertisementOptions) (ok bool) {
	buf.addFlags(0x06)
	if options.LocalName != "" {
		if !buf.addCompleteLocalName(options.LocalName) {
			return false
		}
	}
	// TODO: if there are multiple 16-bit UUIDs, they should be listed in
	// one field.
	// This is not possible for 128-bit service UUIDs (at least not in
	// legacy advertising) because of the 31-byte advertisement packet
	// limit.
	for _, uuid := range options.ServiceUUIDs {
		if !buf.addServiceUUID(uuid) {
			return false
		}
	}
	return true
}

// addFlags adds a flags field to the advertisement buffer. It returns true on
// success (the flags can be added) and false on failure.
func (buf *rawAdvertisementPayload) addFlags(flags byte) (ok bool) {
	if int(buf.len)+3 > len(buf.data) {
		return false // flags don't fit
	}

	buf.data[buf.len] = 2       // length of field (including type)
	buf.data[buf.len+1] = 0x01  // type, 0x01 means Flags
	buf.data[buf.len+2] = flags // the flags
	buf.len += 3
	return true
}

// addCompleteLocalName adds the Complete Local Name field to the advertisement
// buffer. It returns true on success (the name fits) and false on failure.
func (buf *rawAdvertisementPayload) addCompleteLocalName(name string) (ok bool) {
	if int(buf.len)+len(name)+2 > len(buf.data) {
		return false // name doesn't fit
	}

	buf.data[buf.len] = byte(len(name) + 1) // length of field (including type)
	buf.data[buf.len+1] = 9                 // type, 0x09 means Complete Local name
	copy(buf.data[buf.len+2:], name)        // copy the name into the buffer
	buf.len += byte(len(name) + 2)
	return true
}

// addServiceUUID adds a Service Class UUID (16-bit or 128-bit). It has
// currently only been designed for adding single UUIDs: multiple UUIDs are
// stored in separate fields without joining them together in one field.
func (buf *rawAdvertisementPayload) addServiceUUID(uuid UUID) (ok bool) {
	// Don't bother with 32-bit UUID support, it doesn't seem to be used in
	// practice.
	if uuid.Is16Bit() {
		if int(buf.len)+4 > len(buf.data) {
			return false // UUID doesn't fit.
		}
		shortUUID := uuid.Get16Bit()
		buf.data[buf.len+0] = 3    // length of field, including type
		buf.data[buf.len+1] = 0x03 // type, 0x03 means "Complete List of 16-bit Service Class UUIDs"
		buf.data[buf.len+2] = byte(shortUUID)
		buf.data[buf.len+3] = byte(shortUUID >> 8)
		buf.len += 4
		return true
	} else {
		if int(buf.len)+18 > len(buf.data) {
			return false // UUID doesn't fit.
		}
		buf.data[buf.len+0] = 17   // length of field, including type
		buf.data[buf.len+1] = 0x07 // type, 0x07 means "Complete List of 128-bit Service Class UUIDs"
		rawUUID := uuid.Bytes()
		copy(buf.data[buf.len+2:], rawUUID[:])
		buf.len += 18
		return true
	}
}