encode issue

[gsmgxm]

We met a issue, when use python version:

payload whished:
.... 0x20 0x00 0x00 0x00 0xff 0xff 0xff 0xff 0xff 0xff 0xff 0xff 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x01 0x00 0x00 0x00 0x80 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00

result:
.... 0x20 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0xff 0xff 0xff 0xff 0xff 0xff 0xff 0xff 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x01 0x00 0x00 0x00 0x80 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00

Here is our code:
class SApiBbbSendVsbDataReq(prophy.with_metaclass(prophy.struct_generator, prophy.struct)):
_descriptor = [
('transactionId', prophy.u32),
('portId', EBbbPortId),
('vsbTxRegionId', prophy.u32),
('transmissionEnabled', prophy.u32),
('dataLength', prophy.u32),
('data', prophy.array(prophy.u64, size=32)),
]

msg_type = 'SApiBbbSendVsbDataReq'
msg_name = 'API_BBB_SEND_VSB_DATA_REQ_MSG'
hwapi_msg = fsp.syscom.get_hwapi_message(msg_type=msg_type, msg_name=msg_name)
msg_obj = hwapi_msg.get_msg_obj()
msg_obj.transactionId = 0x0000001b
msg_obj.portId = get_EBbbPortId(cell.cpri_link[0])
msg_obj.vsbTxRegionId = 0x00000000
msg_obj.transmissionEnabled = 0x00000001
msg_obj.dataLength = 0x00000020
msg_obj.data[0] = 0xffffffffffffffff
msg_obj.data[1] = 0x0000000000000000
msg_obj.data[2] = 0x0000000800000001

We find between datalength and data there is extra “00 00 00 00”.
I trace the code, found in site-packages\prophy\composite.py
def encode(self, endianness):
data = b""

for field in self._descriptor:
    data += (self._get_padding(len(data), field.type._ALIGNMENT))
    data += field.encode_fcn(self, field.type, getattr(self, field.name, None), endianness)

    if field.type._PARTIAL_ALIGNMENT:
        data += self._get_padding(len(data), field.type._PARTIAL_ALIGNMENT)

data += self._get_padding(len(data), self._ALIGNMENT)

return data

**data += (self._get_padding(len(data), field.type._ALIGNMENT))

len(data) = 20, field.type._ALIGNMENT = 8 ( next data is array u64)**

Why add padding after the previous data(or say 'before the next data') based on next data’s field.type._ALIGNMENT ?

This is why “00000000” was added in payload between “datalength” and “data”.

Is this the right behavior?

Can you help us check it?

[kamichal]

Why add padding after the previous data(or say 'before the next data') based on next data’s field.type._ALIGNMENT ?

This is how C++ structures work. It's natural. Pointers to int64_t have to be aligned to 8 bytes. If you need "pack" feature, check out prophy.struct_packed:

https://prophy.readthedocs.io/en/latest/python_codec.html?highlight=packed#packed-mode

You may also refer to test for example of usage.
https://github.com/aurzenligl/prophy/blob/master/prophy/tests/test_array_ext_sized.py

[gsmgxm]

thank you very much