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fix(hid): correct bSize encoding for HID short items #171

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fix(hid): correct bSize encoding for HID short items #171

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19 changes: 17 additions & 2 deletions facedancer/classes/hid/descriptor.py
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Original file line number Diff line number Diff line change
Expand Up @@ -18,11 +18,26 @@

def _hid_item_generator(constant) -> Tuple[int]:
""" Generates a HID descriptor global item entry. """

# See See HID1.1 [6.2.2.1 Items Types and Tags]
size_code_map = {
0: 0b00, # No data
1: 0b01, # 1 byte
2: 0b10, # 2 bytes
4: 0b11, # 4 bytes
}
# Generate a function that creates a item with
# the relevant type...
def hid_item(*octets):
return (constant | len(octets), *octets)
size = len(octets)
if size not in size_code_map:
raise ValueError(
f"HID short item can only have 0, 1, 2 or 4 data bytes, got {size}"
)

size_code = size_code_map[size]
prefix = constant | size_code

return (prefix, *octets)

# ... and return it.
return hid_item
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