VariableDatum object cannot hold negative signed integers

[DuffyScottC]

VariableDatum objects throw struct.error when you try to store negative signed integers (e.g. -1=b'\xff') in the variableData field, then serialize.

MVP

This is the minimum viable product to reproduce the error

from opendis.dis7 import VariableDatum
from opendis.DataOutputStream import DataOutputStream
from io import BytesIO
import struct

variable_datum = VariableDatum()
data = list((b'\x00'*4)+struct.pack('>i',-1))
variable_datum.variableData = data
variable_datum.variableDatumLength = len(data)*8
memoryStream = BytesIO()
outputStream = DataOutputStream(memoryStream)
variable_datum.serialize(outputStream)
print(memoryStream.getvalue())

Expected Behavior

I expect variable_datum to serialize without an error, and for the final print to display the serialized object (should be b'\x00\x00\x00\x00\x00\x00\x00@\x00\x00\x00\x00\xff\xff\xff\xff')

Actual Behavior

The script throws a struct.error when variable_datum tries to serialize.

Full error

This is the full error that is thrown when variable_datum tries to serialize.

Traceback (most recent call last):
  File "test.py", line 12, in <module>
    variable_datum.serialize(outputStream)
  File "C:\Users\e389403\AppData\Local\Programs\Python\Python37-32\lib\site-packages\opendis\dis7.py", line 3586, in serialize
    outputStream.write_byte(self.variableData[x])
  File "C:\Users\e389403\AppData\Local\Programs\Python\Python37-32\lib\site-packages\opendis\DataOutputStream.py", line 17, in write_byte
    self.stream.write(struct.pack('b', val))
struct.error: byte format requires -128 <= number <= 127

Possible solutions

From what I can gather, when serialize is called:

• serialize() is called
• for each byte in the variableData bytes object, it calls outputStream.write_byte())
  This means that when it reaches b'\xff's, it tries to write 255 as a signed byte to outputStream.
• thus it tries to call struct.pack('b', 255) which results in an error, rightly so because it's out of range(0, 256).

When I changed dis7.py line 3586 to outputStream.write_unsigned_byte(self.variableData[x]), then I got the expected behavior.

Notes

Signed integers actually parse without error. This makes sense, since inputStream.read_byte() is used to parse the bytes when forming the variableData list.

from opendis.dis7 import VariableDatum
from opendis.DataInputStream import DataInputStream
from io import BytesIO

memoryStream = BytesIO(b'\x00\x00\x00\x00\x00\x00\x00@\x00\x00\x00\x00\xff\xff\xff\xff')
inputStream = DataInputStream(memoryStream)
new_variable_datum = VariableDatum()
new_variable_datum.parse(inputStream)
print(new_variable_datum.variableData) # [0, 0, 0, 0, -1, -1, -1, -1]

[leif81]

Thankyou @DuffyScottC . Would you like to submit a PR for this one too?