bin/djbdns-logparse.py

   1 #!/usr/bin/python3
   2 """
   3 Convert tinydns and dnscache logs to human-readable form
   4 """
   5
   6 import re, typing
   7 from struct import pack
   8 from time import strftime, gmtime
   9 from subprocess import Popen, PIPE
  10
  11
  12 ## Regular expressions for matching tinydns/dnscache log lines. We
  13 ## compile these once here rather than within the corresponding
  14 ## matching functions, because the latter get executed repeatedly.
  15
  16 # This first pattern is used to match the timestamp format that the
  17 # tai64nlocal program produces. It appears in both dnscache and
  18 # tinydns lines, after they've been piped through tai64nlocal, of
  19 # course.
  20 timestamp_pat = r'[\d-]+ [\d:\.]+'
  21
  22 # The regex to match dnscache log lines.
  23 dnscache_log_re = re.compile(fr'({timestamp_pat}) (\w+)(.*)')
  24
  25 # The "hex4" pattern matches a string of four hexadecimal digits. This
  26 # is used, for example, by tinydns to encode the query type
  27 # identifier.
  28 hex4_pat = r'[0-9a-f]{4}'
  29
  30 # The IP pattern matches a string of either 8 or 32 hexadecimal
  31 # characters, which correspond to IPv4 and IPv6 addresses,
  32 # respectively, in tinydns logs.
  33 ip_pat = r'[0-9a-f]{8,32}'
  34
  35 # The regex to match tinydns log lines.
  36 tinydns_log_re = re.compile(
  37     rf'({timestamp_pat}) ({ip_pat}):({hex4_pat}):({hex4_pat}) ([\+\-IC/]) ({hex4_pat}) (.*)'
  38 )
  39
  40 # A dictionary mapping query type identifiers, in decimal, to their
  41 # friendly names for tinydns. Reference:
  42 #
  43 #   https://en.wikipedia.org/wiki/List_of_DNS_record_types
  44 #
  45 # Note that mapping here is non-exhaustive, and that tinydns will
  46 # log responses for record types that it does not know about.
  47 query_type = {
  48       1: "a",
  49       2: "ns",
  50       5: "cname",
  51       6: "soa",
  52      12: "ptr",
  53      13: "hinfo",
  54      15: "mx",
  55      16: "txt",
  56      17: "rp",
  57      24: "sig",
  58      25: "key",
  59      28: "aaaa",
  60      33: "srv",
  61      35: "naptr",
  62      38: "a6",
  63      48: "dnskey",
  64      52: "tlsa",
  65      65: "https",
  66     252: "axfr",
  67     255: "any",
  68     257: "caa"
  69 }
  70
  71 # tinydns can drop a query for one of three reasons; this dictionary
  72 # maps the symbol that gets logged in each case to a human-readable
  73 # reason. We include the "+" case here, indicating that the query was
  74 # NOT dropped, to avoid a special case later on when we're formatting
  75 # the human-readable output.
  76 query_drop_reason = {
  77     "+": None,
  78     "-": "no authority",
  79     "I": "invalid query",
  80     "C": "invalid class",
  81     "/": "couldn't parse"
  82 }
  83
  84
  85 def convert_ip(ip : str):
  86     """
  87     Convert a hex string representing an IP address to conventional
  88     human-readable form, ie. dotted-quad decimal for IPv4, and
  89     8 colon-separated hex shorts for IPv6.
  90
  91     Examples
  92     --------
  93
  94         >>> convert_ip("7f000001")
  95         '127.0.0.1'
  96         >>> convert_ip("00000000000000000000ffff7f000001")
  97         '0000:0000:0000:0000:0000:ffff:7f00:0001'
  98
  99     """
 100     if len(ip) == 8:
 101         # IPv4, eg. "7f000001" -> "7f 00 00 01" -> "127.0.0.1"
 102         return "%d.%d.%d.%d" % tuple(pack(">L", int(ip, 16)))
 103     elif len(ip) == 32:
 104         # IPv6 is actually simpler -- it's just a string-slicing operation.
 105         return ":".join([ip[(4*i) : (4*i+4)] for i in range(8)])
 106
 107
 108 def decode_client(words, i):
 109     chunks = words[i].split(":")
 110     if len(chunks) == 2:                # ip:port
 111         words[i] = "%s:%d" % (convert_ip(chunks[0]), int(chunks[1], 16))
 112     elif len(chunks) == 3:
 113         words[i] = "%s:%d (id %d)" % (convert_ip(chunks[0]),
 114                                       int(chunks[1], 16),
 115                                       int(chunks[2], 16))
 116
 117 def decode_ip(words, i):
 118     words[i] = convert_ip(words[i])
 119
 120 def decode_ttl(words, i):
 121     words[i] = "TTL=%s" % words[i]
 122
 123 def decode_serial(words, i):
 124     serial = int(words[i])
 125     words[i] = "#%d" % serial
 126
 127 def decode_type(words, i):
 128     qt = words[i]
 129     words[i] = query_type.get(int(qt), qt)
 130
 131 def handle_dnscache_log(line) -> bool:
 132     match = dnscache_log_re.match(line)
 133     if not match:
 134         return False
 135
 136     (timestamp, event, data) = match.groups()
 137
 138     words = data.split()
 139     if event == "cached":
 140         if words[0] not in ("cname", "ns", "nxdomain"):
 141             decode_type(words, 0)
 142
 143     elif event == "drop":
 144         decode_serial(words, 0)
 145
 146     elif event == "lame":
 147         decode_ip(words, 0)
 148
 149     elif event == "nodata":
 150         decode_ip(words, 0)
 151         decode_ttl(words, 1)
 152         decode_type(words, 2)
 153
 154     elif event == "nxdomain":
 155         decode_ip(words, 0)
 156         decode_ttl(words, 1)
 157
 158     elif event == "query":
 159         decode_serial(words, 0)
 160         decode_client(words, 1)
 161         decode_type(words, 2)
 162
 163     elif event == "rr":
 164         decode_ip(words, 0)
 165         decode_ttl(words, 1)
 166         if words[2] not in ("cname", "mx", "ns", "ptr", "soa"):
 167             decode_type(words, 2)
 168             if words[2] == "a":         # decode answer to an A query
 169                 decode_ip(words, 4)
 170             if words[2] == "txt":       # text record
 171                 response = words[4]
 172                 if response.endswith("..."):
 173                     ellipsis = "..."
 174                     response = response[0:-3]
 175                 else:
 176                     ellipsis = ""
 177                 length = int(response[0:2], 16)
 178                 chars = []
 179                 for i in range(1, len(response)/2):
 180                     chars.append(chr(int(response[2*i : (2*i)+2], 16)))
 181                 words[4] = "%d:\"%s%s\"" % (length, "".join(chars), ellipsis)
 182
 183     elif event == "sent":
 184         decode_serial(words, 0)
 185
 186     elif event == "stats":
 187         words[0] = "count=%s" % words[0]
 188         words[1] = "motion=%s" % words[1]
 189         words[2] = "udp-active=%s" % words[2]
 190         words[3] = "tcp-active=%s" % words[3]
 191
 192     elif event == "tx":
 193         words[0] = "g=%s" % words[0]
 194         decode_type(words, 1)
 195         # words[2] = name
 196         # words[3] = control (domain for which these servers are believed
 197         #            to be authoritative)
 198         for i in range(4, len(words)):
 199             decode_ip(words, i)
 200
 201     elif event in ("tcpopen", "tcpclose"):
 202         decode_client(words, 0)
 203
 204     print(timestamp, event, " ".join(words))
 205     return True
 206
 207
 208 def handle_tinydns_log(line : str) -> bool:
 209     """
 210     Handle a single log line if it matches the ``tinydns_log_re`` regex.
 211
 212     Parameters
 213     ----------
 214
 215     line : string
 216         The log line that might match ``tinydns_log_re``.
 217
 218     Returns
 219     -------
 220
 221     ``True`` if the log line was handled (that is, if it was really a
 222     tinydns log line), and ``False`` otherwise.
 223
 224     Examples
 225     --------
 226
 227         >>> line = "2022-09-14 21:04:40.206516500 7f000001:9d61:be69 - 0001 www.example.com"
 228         >>> handle_tinydns_log(line)
 229         2022-09-14 21:04:40.206516500 dropped query (no authority) from 127.0.0.1:40289 (id 48745): a www.example.com
 230         True
 231
 232         >>> line = "this line is nonsense"
 233         >>> handle_tinydns_log(line)
 234         False
 235
 236     """
 237     match = tinydns_log_re.match(line)
 238     if not match:
 239         return False
 240
 241     (timestamp, ip, port, id, code, type, name) = match.groups()
 242     ip = convert_ip(ip)
 243     port = int(port, 16)
 244     id = int(id, 16)
 245
 246     # Convert the "type" field to a human-readable record type name
 247     # using the query_type dictionary. If the right name isn't present
 248     # in the dictionary, we use the (decimal) type id instead.
 249     type = int(type, 16)                # "001c" -> 28
 250     type = query_type.get(type, type)   # 28 -> "aaaa"
 251
 252     print(timestamp, end=' ')
 253
 254     reason = query_drop_reason[code]
 255     if code == "+":
 256         line_tpl = "sent response to {ip}:{port} (id {id}): {type} {name}"
 257     else:
 258         line_tpl = "dropped query ({reason}) from {ip}:{port}"
 259         if code != "/":
 260             # If the query can actually be parsed, the log line is a
 261             # bit more informative than it would have been otherwise.
 262             line_tpl += " (id {id}): {type} {name}"
 263
 264     print(line_tpl.format(reason=reason,
 265                           ip=ip,
 266                           port=port,
 267                           id=id,
 268                           type=type,
 269                           name=name))
 270     return True
 271
 272
 273 def parse_logfile(file : typing.TextIO):
 274     r"""
 275     Process a single log ``file``.
 276
 277     Parameters
 278     ----------
 279
 280     file : typing.TextIO
 281         An open log file, or stdin.
 282
 283     Examples
 284     --------
 285
 286         >>> line = "@4000000063227a320c4f3114 7f000001:9d61:be69 - 0001 www.example.com\n"
 287         >>> from tempfile import NamedTemporaryFile
 288         >>> with NamedTemporaryFile(mode="w", delete=False) as f:
 289         ...     _ = f.write(line)
 290         >>> f = open(f.name, 'r')
 291         >>> parse_logfile(f)
 292         2022-09-14 21:04:40.206516500 dropped query (no authority) from 127.0.0.1:40289 (id 48745): a www.example.com
 293         >>> f.close()
 294         >>> from os import remove
 295         >>> remove(f.name)
 296
 297     """
 298     # Open pipe to tai64nlocal: we will write lines of our input (the
 299     # raw log file) to it, and read log lines with readable timestamps
 300     # from it.
 301     tai = Popen(["tai64nlocal"], stdin=PIPE, stdout=PIPE, text=True, bufsize=0)
 302
 303     for line in file:
 304         tai.stdin.write(line)
 305         line = tai.stdout.readline()
 306
 307         if not handle_tinydns_log(line):
 308             if not handle_dnscache_log(line):
 309                 print(line, end='')
 310
 311 def main():
 312     r"""
 313     The entry point to the program.
 314
 315     This function is responsible only for parsing any command-line
 316     arguments, and then calling :func`parse_logfile` on them.
 317     """
 318     # Create an argument parser using the file's docsctring as its
 319     # description.
 320     from argparse import ArgumentParser, FileType
 321     parser = ArgumentParser(description = __doc__)
 322
 323     # Parse zero or more positional arguments into a list of
 324     # "logfiles". If none are given, read from stdin instead.
 325     from sys import stdin
 326     parser.add_argument("logfiles",
 327                         metavar="LOGFILE",
 328                         type=FileType("r"),
 329                         nargs="*",
 330                         default=[stdin],
 331                         help="djbdns logfile to process (default: stdin)")
 332
 333     # Warning: argparse automatically opens its file arguments here,
 334     # and they only get closed when the program terminates. There's no
 335     # real benefit to closing them one-at-a-time after calling
 336     # parse_logfile(), because the "scarce" resource of open file
 337     # descriptors gets consumed immediately, before any processing has
 338     # happened. In other words, if you're going to run out of file
 339     # descriptors, it's going to happen right now.
 340     #
 341     # So anyway, don't run this on several million logfiles.
 342     args = parser.parse_args()
 343     for f in args.logfiles:
 344         parse_logfile(f)
 345
 346
 347 if __name__ == "__main__":
 348     main()