How create struct c with python and send on socket

Question

This struct is C code:

struct my_struct_in_c
{
    int port1;
    int port2;
    int port3;
    char ip1[20];
    char ip2[20];
};

how convert above struct c to python?

---

I have test this codes but does not correct deserializer in c:

code1 (does not correct deserializer in c):

res = pack("iii%ss%ss" % (20, 20), 2001, 2002, 2003, b"192.168.1.1", b"192.168.1.2")

code2 (does not correct deserializer in c):

import struct
from collections import namedtuple

format_ = "iii%ss%ss" % (20, 20)

MyStruct = namedtuple("my_struct_in_c", "port1 port2 port3 ip1 ip2")
tuple_to_send = MyStruct(port1=2000,
                         port2=2001,
                         port3=2002,
                         ip1=b"192.168.1.1",
                         ip2=b"192.168.1.2")

string_to_send = struct.pack(format_, *tuple_to_send._asdict().values())

---

Answer 1

As soon as you want to send data over a socket, you have a serialization/deserialization problem. The Python struct module fully handles it, and you can (or must) specify the size of the different elements and the byte ordering (endianness).

C side, beginners often just cast a native struct to a char array and directly use read or write on that... with the unspecified endianness and possible padding problem.

What I mean is that you should never rely on the way C internally stores the struct, but always (de)serialize individual elements in a well defined (size and endianness) way.

Long story made short, without knowing more on the C side, I cannot tell you how you should serialize Python side.