add pcap_fix_udp_len.py and remove turn example

sipp/README.md

@@ -19,17 +19,21 @@ sudo build/sipp -sf scenarios/uac_pcap.xml 127.0.0.1 -m 1
 
 ### Manipulating
 
-Reorder
+#### Reorder
 
 ```bash
 editcap -r g711a.pcap tmp1 2-3 # dump packets 2-3
 editcap -r -t 0.07 g711a.pcap tmp2 1 # dump packet 1 and manipulate timestamp
 editcap g711a.pcap tmp3 1-3 # exclude packets 1-3
 mergecap -w out.pcap -a tmp1 tmp2 tmp3
 ```
-
-Drop
+#### Drop
 
 ```bash
 editcap g711a.pcap out.pcap 2-3 # drop packets 2-3
 ```
+
+#### Remove TURN (4 Bytes, Offset 42 Bytes) encapsulation
+
+editcap -L -C42:4 in.pcap tmp.pcap
+./pcap_fix_udp_len.py tmp.pcap out.pcap 4

sipp/pcap_fix_udp_len.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env python
+
+import argparse
+from scapy.all import *
+
+def update_bytes_from_packet(packet, rbytes):
+    if UDP in packet:
+        # Check if the packet contains a UDP layer
+        packet[UDP].len = packet[UDP].len - int(rbytes)
+        packet[IP].len = packet[IP].len - int(rbytes)
+        packet[UDP].chksum = None  # Recalculate UDP checksum
+        packet[IP].chksum = None  # Recalculate IP checksum
+
+def main():
+    parser = argparse.ArgumentParser(description="Update IP/UDP length.")
+    parser.add_argument("input_file", help="Input PCAP file")
+    parser.add_argument("output_file", help="Output PCAP file")
+    parser.add_argument("rbytes", help="bytes to remove")
+
+    args = parser.parse_args()
+
+    # Load the PCAP file
+    packets = rdpcap(args.input_file)
+
+    for packet in packets:
+            update_bytes_from_packet(packet, args.rbytes)
+
+    # Save the modified PCAP file
+    wrpcap(args.output_file, packets)
+
+    print("PCAP file successfully modified and saved as", args.output_file)
+
+if __name__ == "__main__":
+    main()