diff --git a/examples/wire_read_tcp.py b/examples/wire_read_tcp.py new file mode 100755 index 000000000..e571a65cb --- /dev/null +++ b/examples/wire_read_tcp.py @@ -0,0 +1,49 @@ +#!/usr/bin/python +import argparse +import sys + +import dns.exception +import dns.message + + +def main(): + parser = argparse.ArgumentParser( + description="Read sequence of DNS wire formats prefixed with 2-byte " + "length field - like from TCP socket - and print the messages. This " + "format is used e.g. by dnsperf -B option and dnsgen." + ) + parser.add_argument("infile") + args = parser.parse_args() + ok_msgs = 0 + bad_msgs = 0 + + with open(args.infile, "rb") as infile: + while True: + offset = infile.tell() + len_wire = infile.read(2) + if len(len_wire) == 0: # end of file - expected + break + if len(len_wire) == 1: + raise ValueError("incomplete length preamble, offset", offset) + len_msg = int.from_bytes(len_wire, byteorder="big", signed=False) + print(f"; msg offset 0x{offset + 2:x}, length {len_msg} bytes") + msg_wire = infile.read(len_msg) + if len(msg_wire) != len_msg: + raise ValueError( + f"incomplete message: expected {len_msg} != got {len(msg_wire)}, " + f"length field offset 0x{offset:x}", + ) + try: + msg = dns.message.from_wire(msg_wire) + ok_msgs += 1 + print(msg) + except dns.exception.DNSException as ex: + print(f"; invalid message, skipping: {ex}") + bad_msgs += 1 + print(f"; read {ok_msgs} valid and {bad_msgs} invalid messages") + if bad_msgs: + sys.exit(1) + + +if __name__ == "__main__": + main()