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#!/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
import sys
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:
sys.stderr.write("Saving state {0:s}\n".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:
sys.stderr.write("Restoring state to offset {0:s}\n".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:
sys.stderr.write("{0:s}: Trying to match {1:s} with {2:s}\n".format(
self.state, repr(self.buffer[:10]), repr(re_str)))
match = regex.match(self.buffer)
if match:
if self.verbose > 3:
sys.stderr.write("{0:s} matched {1:s}\n".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:
sys.stderr.write("0x{0:X}: Calling {1:s} {2:s}\n".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:
sys.stderr.write("Default handler: {0:s} with {1:s}\n".format(
token, repr(match.group(0))))
def ERROR(self, message=None, weight=1):
if self.verbose > 0 and message:
sys.stderr.write("Error({0:d}): {1!s}\n".format(weight, message))
self.error += weight
def PUSH_STATE(self, dummy_token=None, dummy_match=None):
if self.verbose > 1:
sys.stderr.write("Storing state {0:s}\n".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:
sys.stderr.write("Returned state to {0:s}\n".format(state))
except IndexError:
sys.stderr.write("Tried to pop the state but failed - possible recursion error\n")
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
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