File: lexer.py

package info (click to toggle)
pytsk 20200117-2
  • links: PTS, VCS
  • area: main
  • in suites: bullseye, sid
  • size: 2,188 kB
  • sloc: ansic: 3,090; python: 3,003; sh: 115; makefile: 68
file content (208 lines) | stat: -rw-r--r-- 6,374 bytes parent folder | download | duplicates (3)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
#!/usr/bin/python
#
# Copyright 2013, Michael Cohen <scudette@gmail.com>.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""A simple feed lexer."""

import re


class Lexer(object):
  """A generic feed lexer."""
  ## The following is a description of the states we have and the
  ## way we move through them: format is an array of
  ## [ state_re, re, token/action, next state ]
  tokens = []
  state = "INITIAL"
  buffer = ""
  error = 0
  verbose = 0
  state_stack = []
  processed = 0
  processed_buffer = ""
  saved_state = None
  flags = 0

  def __init__(self, verbose=0, fd=None):
    super(Lexer, self).__init__()
    self.encoding = "utf-8"

    if not self.verbose:
      self.verbose = verbose

    if len(self.tokens[0]) == 4:
      for row in self.tokens:
        row.append(re.compile(row[0], re.DOTALL))
        row.append(re.compile(row[1], re.DOTALL | re.M | re.S | self.flags))

    self.fd = fd

  def save_state(self, dummy_t=None, m=None):
    """Returns a dict which represents the current state of the lexer.

       When provided to restore_state, the lexer is guaranteed to be
       in the same state as when the save_state was called.

       Note that derived classes may need to extend this.
    """
    ## Unable to save our state if we have errors. We need to guarantee
    ## that we rewind to a good part of the file.
    if self.error:
      return
    try:
      end = m.end()
    except:
      end = 0

    self.saved_state = dict(
        state_stack = self.state_stack[:],
        processed = self.processed - end,
        processed_buffer = self.processed_buffer,
        readptr = self.fd.tell() - len(self.buffer) - end,
        state = self.state,
        objects = self.objects[:],
        error = self.error,
    )
    if self.verbose > 1:
      print("Saving state {0:s}".format(self.processed))

  def restore_state(self):
    state = self.saved_state
    if not state:
      return

    self.state_stack = state["state_stack"]
    self.processed = state["processed"]
    self.processed_buffer = state["processed_buffer"]
    self.buffer = ""
    self.fd.seek(state["readptr"])
    self.state = state["state"]
    self.objects = state["objects"]
    self.error = state["error"]

    if self.verbose > 1:
      print("Restoring state to offset {0:s}".format(self.processed))

  def next_token(self, end=True):
    ## Now try to match any of the regexes in order:
    current_state = self.state
    for _, re_str, token, next_state, state, regex in self.tokens:
      ## Does the rule apply for us now?
      if state.match(current_state):
        if self.verbose > 2:
          print("{0:s}: Trying to match {1:s} with {2:s}".format(
              self.state, repr(self.buffer[:10]), repr(re_str)))
        match = regex.match(self.buffer)
        if match:
          if self.verbose > 3:
            print("{0:s} matched {1:s}".format(
                re_str, match.group(0).encode("utf8")))

          ## The match consumes the data off the buffer (the
          ## handler can put it back if it likes)
          self.processed_buffer += self.buffer[:match.end()]
          self.buffer = self.buffer[match.end():]
          self.processed += match.end()

          ## Try to iterate over all the callbacks specified:
          for t in token.split(","):
            try:
              if self.verbose > 0:
                print("0x{0:X}: Calling {1:s} {2:s}".format(
                    self.processed, t, repr(match.group(0))))
              cb = getattr(self, t, self.default_handler)
            except AttributeError:
              continue

            ## Is there a callback to handle this action?
            callback_state = cb(t, match)
            if callback_state == "CONTINUE":
              continue

            elif callback_state:
              next_state = callback_state
              self.state = next_state

          if next_state:
            self.state = next_state

          return token

    ## Check that we are making progress - if we are too full, we
    ## assume we are stuck:
    if end and len(self.buffer) > 0 or len(self.buffer) > 1024:
      self.processed_buffer += self.buffer[:1]
      self.buffer = self.buffer[1:]
      self.ERROR(
          "Lexer Stuck, discarding 1 byte ({0:s}) - state {1:s}".format(
              repr(self.buffer[:10]), self.state))
      return "ERROR"

    ## No token were found
    return

  def feed(self, data):
    """Feeds the lexer.

    Args:
      data: binary string containing the data (instance of bytes).
    """
    self.buffer += data.decode(self.encoding)

  def empty(self):
    return not len(self.buffer)

  def default_handler(self, token, match):
    if self.verbose > 2:
      print("Default handler: {0:s} with {1:s}".format(
          token, repr(match.group(0))))

  def ERROR(self, message=None, weight=1):
    if self.verbose > 0 and message:
      print("Error({0:s}): {1:s}".format(weight, message))

    self.error += weight

  def PUSH_STATE(self, dummy_token=None, dummy_match=None):
    if self.verbose > 1:
      print("Storing state {0:s}".format(self.state))

    self.state_stack.append(self.state)

  def POP_STATE(self, dummy_token=None, dummy_match=None):
    try:
      state = self.state_stack.pop()
      if self.verbose > 1:
        print("Returned state to {0:s}".format(state))
    except IndexError:
      print("Tried to pop the state but failed - possible recursion error")
      state = None
    return state

  def close(self):
    """Just a conveniece function to force us to parse all the data."""
    while self.next_token():
      pass


class SelfFeederMixIn(Lexer):
  """This mixin is used to make a lexer which feeds itself one
     sector at the time.

     Note that self.fd must be the fd we read from.
  """
  def parse_fd(self, fd):
    self.feed(fd.read())
    while self.next_token():
      pass