pack and unpack at the right format in python

Question

I'm looking to unpack from a buffer a string and its length.

For example to obtain (4, 'Gégé') from this buffer :
b'\\x00\\x04G\\xE9g\\xe9'

Does someone know how to do ?

Answer 1

The length data looks like a big-endian unsigned 16 bit integer, and the string data looks like it's using the Latin1 encoding. If that's correct, you can extract it like this:

from struct import unpack

def extract(buff):
    return unpack(b'>H', buff[:2])[0], buff[2:].decode('latin1')

buff = b'\x00\x04G\xE9g\xe9'
print(extract(buff))

output

(4, 'Gégé')

Another possibility for the encoding is the old Windows code page 1252 , which can be decoded using .decode('cp1252') .

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The above code works in both Python 2 & Python 3. But in Python 3 there's an easier way: we don't need struct.unpack , we can use the int.from_bytes method.

def extract(buff):
    return int.from_bytes(buff[:2], 'big'), buff[2:].decode('latin1')