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[core] Fix stalled connection that should break after rogue NAK/ACK r…
…eception
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Mikolaj Malecki
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Jan 14, 2025
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,168 @@ | ||
| #!/usr/bin/python3 | ||
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| # This script is a testing tool that inserts a packet interceptor for | ||
| # a bond between two local ports and modify a packet that is sent over | ||
| # the UDP link used by the SRT connection. | ||
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| # Provided by: | ||
| # https://github.com/FelixSodermanNeti | ||
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| import socket, select, argparse | ||
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| class UDPProxy: | ||
| def __init__(self, caller_host, caller_port, listener_host, listener_port, break_at_pkt_NAK, break_at_pkt_ACK): | ||
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| # Listening socket configuration | ||
| self.caller_host = caller_host | ||
| self.caller_port = caller_port | ||
| self.caller_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) | ||
| self.caller_socket.bind((self.caller_host, self.caller_port)) | ||
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| # Forwarding destination configuration | ||
| self.listener_host = listener_host | ||
| self.listener_port = listener_port | ||
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| # Client address tracking | ||
| self.client_address = None | ||
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| # Proxy state | ||
| self.running = False | ||
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| # Break SRT | ||
| self.sentPacketCounter = 0 | ||
| self.recivedAckCounter = 0 | ||
| self.PACKETBREAK_NAK = break_at_pkt_NAK | ||
| self.PACKETBREAK_ACK = break_at_pkt_ACK | ||
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| def start(self): | ||
| try: | ||
| self.running = True | ||
| print( | ||
| f"UDP Proxy started. Listening on {self.caller_host}:{self.caller_port}. " | ||
| f"Forwarding to {self.listener_host}:{self.listener_port}" | ||
| ) | ||
|
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| # Create forward socket | ||
| listener_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) | ||
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| # Use select for non-blocking I/O | ||
| while self.running: | ||
| readable, _, _ = select.select([self.caller_socket, listener_socket], [], [], 1) | ||
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| for sock in readable: | ||
| if sock == self.caller_socket: | ||
| # Receive from client | ||
| data, addr = sock.recvfrom(65535) | ||
| self.client_address = addr | ||
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| #Modify the NAK | ||
| processedData = data | ||
| # NAK | ||
| if(data[1] == 0x03 and len(data) == 24 and self.PACKETBREAK_NAK != 0): # IS A NAK, This should check for a 1 in the first byte aswell. | ||
| print("Modifying NAK.") | ||
| newBytes = b"\xff\xff\xff\xff" | ||
| processedData = data[:20] + newBytes + data[20 + len(newBytes):] | ||
| """ | ||
| print("NAK BEFORE:") | ||
| print(string_bytearray_in_rows(data=data)) | ||
| print("\n\nModifying NAK.\n\n") | ||
| print("ŃAK AFTER:") | ||
| print(string_bytearray_in_rows(data=processedData)) | ||
| """ | ||
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| # ACK | ||
| if(data[1] == 0x02 and len(data) == 44): # IS A ACK | ||
| self.recivedAckCounter += 1 | ||
| if (self.PACKETBREAK_ACK != 0 and self.recivedAckCounter == self.PACKETBREAK_ACK): | ||
| print("Modifying ACK.") | ||
| newBytes = b"\x7f\xff\xff\xff" | ||
| offset = 16 | ||
| processedData = data[:offset] + newBytes + data[offset + len(newBytes):] | ||
| """ | ||
| print("ACK BEFORE:") | ||
| print(string_bytearray_in_rows(data=data)) | ||
| print("\n\nModifying ACK.\n\n") | ||
| print("ACK AFTER:") | ||
| print(string_bytearray_in_rows(data=processedData)) | ||
| """ | ||
| listener_socket.sendto( | ||
| processedData, | ||
| (self.listener_host, self.listener_port) | ||
| ) | ||
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| elif sock == listener_socket: | ||
| # Receive from server | ||
| data, addr = sock.recvfrom(65535) | ||
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| # Drop a sequence of data packets (as to atleast 3 to trigger an NAK with a range) | ||
| if len(data) == 1332: # Packet with data | ||
| self.sentPacketCounter += 1 | ||
| if (self.PACKETBREAK_NAK != 0 and self.sentPacketCounter in range(self.PACKETBREAK_NAK, self.PACKETBREAK_NAK+5)): | ||
| print("Discarding packet.") | ||
| continue | ||
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| if not self.client_address: | ||
| print("No client to send data to!") | ||
| continue | ||
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| self.caller_socket.sendto( | ||
| data, | ||
| self.client_address | ||
| ) | ||
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| except Exception as e: | ||
| print(f"Proxy error: {e}") | ||
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| finally: | ||
| self.stop() | ||
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| def stop(self): | ||
| self.running = False | ||
| self.caller_socket.close() | ||
| print("UDP Proxy stopped.") | ||
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| def string_bytearray_in_rows(data, bytes_per_row=4): | ||
| tmpString = "\n" | ||
| for i in range(0, len(data), bytes_per_row): | ||
| row = data[i:i+bytes_per_row] | ||
| tmpString += f"{i}: " | ||
| tmpString += (" ".join(f"{byte:02x}" for byte in row)) | ||
| tmpString += "\n" | ||
| tmpString += "\n" | ||
| return tmpString | ||
|
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||
| def main(): | ||
| # Parse command-line arguments | ||
| parser = argparse.ArgumentParser(description='UDP Proxy') | ||
| parser.add_argument('--caller-host', default='127.0.0.1', | ||
| help='Host to listen on (srt caller) (default: 127.0.0.1)') | ||
| parser.add_argument('--caller-port', type=int, required=True, | ||
| help='Port to listen on (srt caller)') | ||
| parser.add_argument('--listener-host', default='127.0.0.1', | ||
| help='Destination host to forward packets (srt listener)') | ||
| parser.add_argument('--listener-port', type=int, required=True, | ||
| help='Destination port to forward packets (srt listener)') | ||
| parser.add_argument('--break-at-pkt-NAK', type=int, default=0, | ||
| help='At what datapacket should the NAK -1 be sent (0=never)') | ||
| parser.add_argument('--break-at-pkt-ACK', type=int, default=0, | ||
| help='At what datapacket should the ACK -1 be sent (0=never)') | ||
| args = parser.parse_args() | ||
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| # Create and start proxy | ||
| proxy = UDPProxy( | ||
| args.caller_host, | ||
| args.caller_port, | ||
| args.listener_host, | ||
| args.listener_port, | ||
| args.break_at_pkt_NAK, | ||
| args.break_at_pkt_ACK | ||
| ) | ||
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| try: | ||
| proxy.start() | ||
| except KeyboardInterrupt: | ||
| proxy.stop() | ||
|
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||
| if __name__ == '__main__': | ||
| main() |
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