djbdns/tinydns.py

   1 # Don't clobber the global compile() with a named import.
   2 import re
   3
   4 from typing import Optional
   5 from djbdns.common import *
   6
   7 # The "hex4" pattern matches a string of four hexadecimal digits. This
   8 # is used, for example, by tinydns to encode the query type
   9 # identifier.
  10 hex4_pat = r'[0-9a-f]{4}'
  11
  12 # The IP pattern matches a string of either 8 or 32 hexadecimal
  13 # characters, which correspond to IPv4 and IPv6 addresses,
  14 # respectively, in tinydns logs.
  15 ip_pat = r'[0-9a-f]{8,32}'
  16
  17 # The regex to match tinydns log lines.
  18 tinydns_log_re = re.compile(
  19     rf'({timestamp_pat}) ({ip_pat}):({hex4_pat}):({hex4_pat}) ([\+\-IC/]) ({hex4_pat}) (.*)'
  20 )
  21
  22 # tinydns can drop a query for one of three reasons; this dictionary
  23 # maps the symbol that gets logged in each case to a human-readable
  24 # reason. We include the "+" case here, indicating that the query was
  25 # NOT dropped, to avoid a special case later on when we're formatting
  26 # the human-readable output.
  27 query_drop_reason = {
  28     "+": None,
  29     "-": "no authority",
  30     "I": "invalid query",
  31     "C": "invalid class",
  32     "/": "couldn't parse"
  33 }
  34
  35
  36 def handle_tinydns_log(line : str) -> Optional[str]:
  37     r"""
  38     Handle a single log line if it matches the ``tinydns_log_re`` regex.
  39
  40     Parameters
  41     ----------
  42
  43     line : string
  44         The log line that might match ``tinydns_log_re``.
  45
  46     Returns
  47     -------
  48
  49     Either the human-readable string if the log line was handled (that
  50     is, if it was really a tinydns log line), or ``None`` if it was
  51     not.
  52
  53     Examples
  54     --------
  55
  56         >>> line = "2022-09-14 21:04:40.206516500 7f000001:9d61:be69 - 0001 www.example.com"
  57         >>> handle_tinydns_log(line)
  58         '2022-09-14 21:04:40.206516500 dropped query (no authority) from 127.0.0.1:40289 (id 48745): a www.example.com'
  59
  60         >>> line = "this line is nonsense"
  61         >>> handle_tinydns_log(line)
  62
  63     """
  64     match = tinydns_log_re.match(line)
  65     if not match:
  66         return None
  67
  68     (timestamp, ip, port, id, code, type, name) = match.groups()
  69     ip = convert_ip(ip)
  70     port = int(port, 16)
  71     id = int(id, 16)
  72
  73     # Convert the "type" field to a human-readable record type name
  74     # using the query_type dictionary. If the right name isn't present
  75     # in the dictionary, we use the (decimal) type id instead.
  76     type = int(type, 16)                # "001c" -> 28
  77     type = query_type.get(type, type)   # 28 -> "aaaa"
  78
  79     line_tpl = "{timestamp} "
  80
  81     reason = query_drop_reason[code]
  82     if code == "+":
  83         line_tpl += "sent response to {ip}:{port} (id {id}): {type} {name}"
  84     else:
  85         line_tpl += "dropped query ({reason}) from {ip}:{port}"
  86         if code != "/":
  87             # If the query can actually be parsed, the log line is a
  88             # bit more informative than it would have been otherwise.
  89             line_tpl += " (id {id}): {type} {name}"
  90
  91     return line_tpl.format(timestamp=timestamp,
  92                            reason=reason,
  93                            ip=ip,
  94                            port=port,
  95                            id=id,
  96                            type=type,
  97                            name=name)