94 lines
2.6 KiB
Python
94 lines
2.6 KiB
Python
# Helpers for generating BLE advertising payloads.
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from micropython import const
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import struct
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import bluetooth
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# Advertising payloads are repeated packets of the following form:
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# 1 byte data length (N + 1)
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# 1 byte type (see constants below)
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# N bytes type-specific data
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_ADV_TYPE_FLAGS = const(0x01)
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_ADV_TYPE_NAME = const(0x09)
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_ADV_TYPE_UUID16_COMPLETE = const(0x3)
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_ADV_TYPE_UUID32_COMPLETE = const(0x5)
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_ADV_TYPE_UUID128_COMPLETE = const(0x7)
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_ADV_TYPE_UUID16_MORE = const(0x2)
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_ADV_TYPE_UUID32_MORE = const(0x4)
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_ADV_TYPE_UUID128_MORE = const(0x6)
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_ADV_TYPE_APPEARANCE = const(0x19)
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# Generate a payload to be passed to gap_advertise(adv_data=...).
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def advertising_payload(limited_disc=False, br_edr=False, name=None, services=None, appearance=0):
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payload = bytearray()
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def _append(adv_type, value):
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nonlocal payload
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payload += struct.pack("BB", len(value) + 1, adv_type) + value
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_append(
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_ADV_TYPE_FLAGS,
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struct.pack("B", (0x01 if limited_disc else 0x02) + (0x18 if br_edr else 0x04)),
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)
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if name:
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_append(_ADV_TYPE_NAME, name)
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if services:
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for uuid in services:
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b = bytes(uuid)
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if len(b) == 2:
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_append(_ADV_TYPE_UUID16_COMPLETE, b)
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elif len(b) == 4:
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_append(_ADV_TYPE_UUID32_COMPLETE, b)
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elif len(b) == 16:
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_append(_ADV_TYPE_UUID128_COMPLETE, b)
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# See org.bluetooth.characteristic.gap.appearance.xml
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if appearance:
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_append(_ADV_TYPE_APPEARANCE, struct.pack("<h", appearance))
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return payload
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def decode_field(payload, adv_type):
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i = 0
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result = []
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while i + 1 < len(payload):
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if payload[i + 1] == adv_type:
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result.append(payload[i + 2 : i + payload[i] + 1])
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i += 1 + payload[i]
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return result
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def decode_name(payload):
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n = decode_field(payload, _ADV_TYPE_NAME)
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return str(n[0], "utf-8") if n else ""
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def decode_services(payload):
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services = []
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for u in decode_field(payload, _ADV_TYPE_UUID16_COMPLETE):
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services.append(bluetooth.UUID(struct.unpack("<h", u)[0]))
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for u in decode_field(payload, _ADV_TYPE_UUID32_COMPLETE):
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services.append(bluetooth.UUID(struct.unpack("<d", u)[0]))
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for u in decode_field(payload, _ADV_TYPE_UUID128_COMPLETE):
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services.append(bluetooth.UUID(u))
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return services
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def demo():
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payload = advertising_payload(
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name="micropython",
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services=[bluetooth.UUID(0x181A), bluetooth.UUID("6E400001-B5A3-F393-E0A9-E50E24DCCA9E")],
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)
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print(payload)
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print(decode_name(payload))
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print(decode_services(payload))
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if __name__ == "__main__":
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demo()
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