Python3 How to get raw bytes string without encode?

Question

I want to get a string of origin bytes (assemble code) without encoding to another encoding. As the content of bytes is shellcode, I do not need to encode it and want to write it directly as raw bytes. By simplify, I want to convert "b'\xb7\x00\x00\x00'" to "\xb7\x00\x00\x00" and get the string representation of raw bytes. For example:

>> byte_code = b'\xb7\x00\x00\x00\x05\x00\x00\x00\x95\x00\x00\x00\x00\x00\x00\x00'
>> uc_str = str(byte_code)[2:-1] 
>> print(byte_code, uc_str)
b'\xb7\x00\x00\x00\x05\x00\x00\x00\x95\x00\x00\x00\x00\x00\x00\x00' \xb7\x00\x00\x00\x05\x00\x00\x00\x95\x00\x00\x00\x00\x00\x00\x00

Currently I have only two ugly methods,

>> uc_str = str(byte_code)[2:-1]
>> uc_str = "".join('\\x{:02x}'.format(c) for c in byte_code)

Raw bytes usage:

>> my_template = "const char byte_code[] = 'TPL'"
>> uc_str = str(byte_code)[2:-1]
>> my_code = my_template.replace("TPL", uc_str)
# then write my_code to xx.h

Is there any pythonic way to do this?

wim · Accepted Answer · 2020-09-22 08:12:54Z

2

Your first method is broken, because any bytes that can be represented as printable ASCII will be, for example:

>>> str(b'\x00\x20\x41\x42\x43\x20\x00')[2:-1]
'\\x00 ABC \\x00'

The second method is actually okay. Since this feature appears to be missing from stdlib I've published all-escapes which provides it.

pip install all-escapes

Example usage:

>>> b"\xb7\x00\x00\x00".decode("all-escapes")
'\\xb7\\x00\\x00\\x00'

edited Sep 22, 2020 at 8:12

answered Sep 18, 2020 at 6:35

wim

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3 Comments

fripSide Over a year ago

This is because I want to insert the byte_code to a string template and then write to a .cpp file.

wim Over a year ago

Then the wording in the question is a little misleading - you don't want to write it directly as raw bytes, you want to write a string representation of the bytes.

fripSide Over a year ago

Yes. I have modified the description in the question and gave a simple example for why I need to do this.

Ben Fischer · Accepted Answer · 2022-03-01 23:09:30Z

1

I came across this trying to do something similar with some SNMP code.

byte_code = b'\xb7\x00\x00\x00\x05\x00\x00\x00\x95\x00\x00\x00\x00\x00\x00\x00'
text = byte_code.decode('raw_unicode_escape')
writer_func(text)

It worked to send an SNMP Hex string as an OctetString when there was no helper support for hex.

See also standard-encodings and bytes decode

and for anyone looking at the SNMP Set Types

answered Mar 1, 2022 at 23:09

Ben Fischer

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Comments

Emmanuel DUMAS · Accepted Answer · 2020-09-18 06:10:25Z

-1

basic of conversion byte / str is this :

>>> b"abc".decode()
'abc'
>>>

or :

>>> sb = b"abc"
>>> s = sb.decode()
>>> s
'abc'
>>>

The inverse is :

>>> "abc".encode()
b'abc'
>>>

or :

>>> s="abc"
>>> sb=s.encode()
>>> sb
b'abc'
>>>

And in your case, you should use errors argument :

>>> b"\xb7".decode(errors="replace")
'�'
>>>

answered Sep 18, 2020 at 6:10

Emmanuel DUMAS

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